5. Haematology

5. Haematology

Presented by: Prof.Mirza Anwar BaigAnjuman-I-Islam's Kalsekar Technical Campus

School of Pharmacy,New Pavel,Navi Mumbai,Maharashtra

Contents:

1. Composition of blood2. Functions of blood elements3. Erythropoiesis and life cycle of RBC.4. Synthesis of Haemoglobin5. Leucopoiesis6. Immunity: Basics and Types7. Coagulation of blood8. Blood groups

Learning outcomes1.Describe the chemical composition of plasma

1.Discuss the structure, function and formation of red blood cells, including the systems used in medicine to classify the different types

3.Discuss the functions and formation of the different types of white blood cell

4. Outline the role of platelets in blood clotting.

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What is Blood ?

•Blood is a connective tissue. It provides one of the means of communication between the cells of different parts of the body and the external environment.

•Blood makes up about 7% of body weight (about 5.6 litres in a 70 kg man).

•Blood in the blood vessels is always in motion. The continual flow maintains a fairly constant environment for the body cells.

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COMPOSITION OF BLOOD

•Blood is composed of a straw-coloured transparent fluid,

plasma, in which different types of cells are suspended.

•Plasma constitutes about 55% and cells about 45% of

blood volume.

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Figure 19.1b

Composition of Whole Blood

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Figure 19.1c

Composition of Whole Blood

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Table 17.19

Erythrocytes – Red Blood Cells (RBCs)

• Oxygen-transporting cells – 7.5 µm in diameter (diameter of capillary 8 –

10µm)

• Most numerous of the formed elements– Females: 4.3 – 5.2 million cells/cubic millimeter– Males: 5.2 – 5.8 million cells/cubic millimeter

• Made in the red bone marrow in long bones, cranial bones, ribs, sternum, and vertebrae

• Average lifespan 100 – 120 days

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RBC Structure And Function

• Have no organelles or nuclei

• Can neither reproduce nor carry extensive metabolic activities.

• Hemoglobin in cytoplasm – oxygen carrying protein

– Each RBC has about 280 million hemoglobin molecules

• Biconcave shape – 30% more surface area

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Routine assessments in clinical practice• Erythrocyte count.

This is the number of erythrocytes per litre or per cubic millimetre (mm3) of blood.

• Packed cell volume or haematocrit.

This is the volume of red cells in 1 litre or 1 mm3 of whole blood.

• Mean cell volume.

This is the average volume of cells, measured in femtolitres

(fl = 10-15 litre).

• Haemoglobin.

This is the weight of haemoglobin in whole blood, measured in grams per 100 ml.

• Mean cell haemoglobin.

This is the average amount of haemoglobin in each cell, measured in picograms (pg = 10-12 gram).

• Mean cell haemoglobin concentration.

This is the amount of haemoglobin in 100 ml of red cells.12

RBC Life Cycle

1. Red blood cells live only about 120 days because of the wear and tear their plasma membranes undergo as they squeeze through blood capillaries.

2. Without a nucleus and other organelles, RBCs cannot synthesize new components to replace damaged ones.

3. Ruptured red blood cells are removed from circulation and destroyed by fixed phagocytic macrophages in the spleen and liver

Life cycle of RBC:

Development and life span of erythrocytes

• Erythrocytes are formed in red bone marrow, which is present in the ends of long bones and in flat and irregular bones.

• They pass through several stages of development

before entering the blood. Their life span in the circulation is about 120 days.

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Erythropoiesis

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The process of development of red blood cells from pluripotent stem cells takes about 7 days and is called erythropoiesis. •It is characterised by two main features:

A. Maturation of the cell

B. Formation of haemoglobin inside the

cell

A. Maturation of the cell.

1.During this process the cell decreases in size and loses its nucleus.

2.These changes depend on especially the presence of vitamin B12 and folic acid. These are present in sufficient quantity in a normal diet, stored in the liver.

3. Absorption of vitamin B12 depends on a glycoprotein called intrinsic factor secreted by parietal cells in the gastric glands.

4. Together they form the intrinsic factor-vitamin B12 complex (IF-B12).

5. During its passage through the intestines, the bound vitamin is protected from enzymatic digestion, and is absorbed in the terminal ileum.

6. Folic acid is absorbed in the duodenum and jejunum

7. Deficiency of either vitamin B12 or folic acid leads to impaired red cell production.

Formation of haemoglobin

1. Haemoglobin is synthesised inside developing erythrocytes in red bone marrow.

2. Haemoglobin in mature erythrocytes combines with oxygen to form oxyhaemoglobin, giving arterial blood its characteristic red colour.

3. In this way the bulk of oxygen absorbed from the lungs is transported around the body to maintain a continuous oxygen supply to all cells.

4. Haemoglobin is also involved, to a lesser extent, in the transport of carbon dioxide from the body cells to the lungs for excretion.

5. Each haemoglobin molecule contains four atoms of iron. Each atom can carry one molecule of oxygen, therefore one haemoglobin molecule can carry up to four molecules of oxygen.

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Destruction of erythrocytesØ The life span of erythrocytes is about 120 days and their breakdown, or haemolysis, is carried out by phagocytic reticuloendothelial cells. Ø These cells are found in many tissues but the main sites of haemolysis are the spleen, bone marrow and liver. Ø As erythrocytes age, changes in their cell membranes make them more susceptible to haemolysis.Ø Iron released by haemolysis is retained in the body and reused in the bone marrow to form haemoglobin. Biliverdin is formed from the protein part of the erythrocytes.Ø It is almost completely reduced to the yellow pigment bilirubin, before it is bound to plasma globulin and transported to the liver. Ø In the liver it is changed from a fat-soluble to a water-soluble form before it is excreted as a constituent of bile.

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Hemostasis

1. Vasoconstriction.i. When platelets come in contact with a damaged blood vessel, their surface becomes sticky and they adhere to the damaged wall.

ii. They then release serotonin (5-hydroxytryptamine), which constricts (narrows) the vessel, reducing blood flow through it. Other chemicals that cause vasoconstriction, e.g. thromboxanes,are released by the damaged vessel itself.

2. Platelet plug formation. i. The adherent platelets clump to each other and release other substances, including adenosine diphosphate (ADP), which attract more platelets to the site. ii. Passing platelets stick to those already at the damaged vessel and they too release their chemicals. This is a positive feedback system by which many platelets rapidly arrive at the site of vascular damage and quickly form a temporary seal — the platelet plug.

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3. Coagulation (blood clotting). Blood coagulation refers to the process of forming a clot to stop bleeding.Ø This is a complex process that also involves a positive feedback system. Ø Their numbers represent the order in which they were discovered and not the order of participation in the clotting process. Ø These factors activate each other and known as the clotting cascade.Ø Blood clotting results in formation of an insoluble thread-like mesh of fibrin which traps blood cells and is much stronger than the rapidly formed platelet plug. Ø In the final stages of this process prothrombin activator acts on the plasma protein prothrombin converting it to thrombin.

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Hemostasis:

•The clotting cascade occurs through two separate pathways that interact, the intrinsic and the extrinsic pathway. 1. Extrinsic Pathway:The extrinsic pathway is activated by external trauma that causes blood to escape from the vascular system. This pathway is quicker than the intrinsic pathway. It involves factor VII.2. Intrinsic Pathway:The intrinsic pathway is activated by trauma inside the vascular system, and is activated by platelets, exposed endothelium, chemicals, or collagen. This pathway is slower than the extrinsic pathway, but more important. It involves factors XII, XI, IX, VIII.3. Common Pathway:Both pathways meet and finish the pathway of clot production in common pathway. The common pathway involves factors I, II, V, and X.

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Coagulation Pathway:

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This initial pathway is independent of Factor VIII (factor missing in hemophilia A) and Factor IX (factor missing in hemophilia B). When the body has made a small amount of fibrin, a substance known as Tissue Factor Pathway Inhibitor (TFPI) is released. This inhibitor binds to the TF:FVIIa/FXa complex, preventing further formation of factor FXa. It is thought that TFPI is released to protect against overreation of the coagulation system. At this point, the intrinsic pathway is activated.

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Immunity- Basics and types

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Immunity: Two Intrinsic Defense Systems

1. Innate (nonspecific) system responds quickly and consists of:

– First line of defense – intact skin and mucosae prevent entry of microorganisms

– Second line of defense – antimicrobial proteins, phagocytes, and other cells

•Inhibit spread of invaders throughout the body

•Inflammation is its hallmark and most important mechanism

COMPILED BY: PROF.ANWAR BAIG (AIKTC,SOP)

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Immunity: Two Intrinsic Defense Systems

2. Adaptive (specific) defense system

– Third line of defense – mounts attack against particular foreign substances

•Takes longer to react than the innate system

•Works in conjunction with the innate system


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First Line of Defense

1. Surface Barriers

• Skin, mucous membranes, and their secretions make up the first line of defense

• Keratin in the skin:

– Presents a physical barrier to most microorganisms

– Is resistant to weak acids and bases, bacterial enzymes, and toxins

• Mucosae provide similar mechanical barriers


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2. Epithelial Chemical Barriers

• Epithelial membranes produce protective chemicals that destroy microorganisms

– Skin acidity (pH of 3 to 5) inhibits bacterial growth

– Sebum contains chemicals toxic to bacteria

– Stomach mucosae secrete concentrated HCl and protein-digesting enzymes

– Saliva and lacrimal fluid contain lysozyme

– Mucus traps microorganisms that enter the digestive and respiratory systems


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3. Respiratory Tract Mucosae

• Mucus-coated hairs in the nose trap inhaled particles

• Mucosa of the upper respiratory tract is ciliated

– Cilia sweep dust- and bacteria-laden mucus away from lower respiratory passages


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Internal Defenses (Second Line of Defense)

The body uses nonspecific cellular and chemical devices to protect itself

1. Phagocytes 2. natural killer (NK) cells3. Inflammatory response enlists macrophages, mast

cells, WBCs, and chemicals4. Antimicrobial proteins in blood and tissue fluid

Harmful substances are identified by surface carbohydrates unique to infectious organisms


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1. Phagocytes

• Macrophages are the chief phagocytic cells• Free macrophages wander throughout a region

in search of cellular debris• Kupffer cells (liver) and microglia (brain) are

fixed macrophages• Neutrophils become phagocytic when

encountering infectious material• Eosinophils are weakly phagocytic against

parasitic worms• Mast cells bind and ingest a wide range of

bacteria


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Mechanism of Phagocytosis

• Microbes adhere to the phagocyte• Pseudopods engulf the particle

(antigen) into a phagosome• Phagosomes fuse with a lysosome to

form a phagolysosome• Invaders in the phagolysosome are

digested by proteolytic enzymes• Indigestible and residual material is

removed by exocytosisCOMPILED BY: PROF.ANWAR BAIG

(AIKTC,SOP)

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Mechanism of Phagocytosis

Figure 21.1a, bCOMPILED BY: PROF.ANWAR BAIG (AIKTC,SOP)

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2. Natural Killer (NK) Cells

• Cells that can lyse and kill cancer cells and virus-infected cells

• Natural killer cells: – Are a small, distinct group of large granular

lymphocytes – React nonspecifically and eliminate cancerous

and virus-infected cells– Kill their target cells by releasing perforins and

other cytolytic chemicals– Secrete potent chemicals that enhance the

inflammatory response


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3. Inflammation: Tissue Response to Injury

• The inflammatory response is triggered whenever body tissues are injured – Prevents the spread of damaging agents

to nearby tissues– Disposes of cell debris and pathogens– Sets the stage for repair processes

• The four cardinal signs of acute inflammation are redness, heat, swelling, and pain


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Inflammation Response

• Begins with a flood of inflammatory chemicals released into the extracellular fluid

• Inflammatory mediators (chemicals) :– Include kinins, prostaglandins (PGs),

complement, and cytokines – Are released by injured tissue, phagocytes,

lymphocytes, and mast cells– Cause local small blood vessels to dilate,

resulting in hyperemia COMPILED BY: PROF.ANWAR BAIG

(AIKTC,SOP)

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Toll-like Receptors (TLRs)

• Macrophages and cells lining the gastrointestinal and respiratory tracts bear TLRs

• TLRs recognize specific classes of infecting microbes

• Activated TLRs trigger the release of cytokines that promote inflammation


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Inflammatory Response: Vascular Permeability

• Chemicals liberated by the inflammatory response increase the permeability of local capillaries

• Exudate (fluid containing proteins, clotting factors, and antibodies): – Seeps into tissue spaces causing local

edema (swelling), which contributes to the sensation of pain


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Inflammatory Response: Edema

• The surge of protein-rich fluids into tissue spaces (edema):– Helps to dilute harmful substances– Brings in large quantities of oxygen and

nutrients needed for repair– Allows entry of clotting proteins, which

prevents the spread of bacteria


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• Occurs in four main phases:– Leukocytosis – neutrophils are released

from the bone marrow in response to leukocytosis-inducing factors released by injured cells

– Margination – neutrophils cling to the walls of capillaries in the injured area

– Diapedesis – neutrophils squeeze through capillary walls and begin phagocytosis

– Chemotaxis – inflammatory chemicals attract neutrophils to the injury site

Inflammatory Response: Phagocytic Mobilization


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Neutrophils enter blood from bone marrow

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Margination

Diapedesis

Positivechemotaxis

Capillary wall EndotheliumBasal lamina

Inflammatory chemicals diffusing from the inflamed site act as chemotactic agents

Inflammatory Response: Phagocytic Mobilization

Figure 21.3COMPILED BY: PROF.ANWAR BAIG

(AIKTC,SOP)

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Flowchart of Events in Inflammation

Figure 21.2

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4. Antimicrobial Proteins

• Enhance the innate defenses by:– Attacking microorganisms directly– Hindering microorganisms’ ability to

reproduce• The most important antimicrobial

proteins are:– Interferon– Complement proteins


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• Abnormally high body temperature in response to invading microorganisms

• The body’s thermostat is reset upwards in response to pyrogens, chemicals secreted by leukocytes and macrophages exposed to bacteria and other foreign substances

Fever


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• High fevers are dangerous as they can denature enzymes

• Moderate fever can be beneficial, as it causes:– The liver and spleen to sequester iron and

zinc (needed by microorganisms)– An increase in the metabolic rate, which

speeds up tissue repair

Fever


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• The adaptive immune system is a functional system that:– Recognizes specific foreign substances– Acts to immobilize, neutralize, or destroy

foreign substances– Amplifies inflammatory response and

activates complement

Adaptive (Specific) Defenses (Third Line of Defense)


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• The adaptive immune system is antigen-specific, systemic, and has memory

• It has two separate but overlapping arms– Humoral, or antibody-mediated (B Cell)

immunity– Cellular, or cell-mediated (T Cell) immunity

Adaptive Immune Defenses


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• Substances that can mobilize the immune system and provoke an immune response

• The ultimate targets of all immune responses are mostly large, complex molecules not normally found in the body (nonself)

Antigens


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• Important functional properties:– Immunogenicity – the ability to stimulate

proliferation of specific lymphocytes and antibody production

– Reactivity – the ability to react with the products of the activated lymphocytes and the antibodies released in response to them

• Complete antigens include foreign protein, nucleic acid, some lipids, and large polysaccharides

Complete Antigens


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• Small molecules, such as peptides, nucleotides, and many hormones, – not immunogenic (does not stimulate a response) – reactive when attached to protein carriers

• If they link up with the body’s proteins, the adaptive immune system may recognize them as foreign and mount a harmful attack (allergy)

• Haptens are found in poison , some detergents, and cosmetics

Haptens (Incomplete Antigens)


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• Only certain parts of an entire antigen are immunogenic

• Antibodies and activated lymphocytes bind to these antigenic determinants

• Most naturally occurring antigens have numerous antigenic determinants that:– Mobilize several different lymphocyte

populations– Form different kinds of antibodies against

it.

Antigenic Determinants


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Antigenic Determinants


(AIKTC,SOP)

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• Two types of lymphocytes– B lymphocytes – oversee humoral

immunity– T lymphocytes – non-antibody-producing

cells that constitute the cell-mediated arm of immunity

• Antigen-presenting cells (APCs):– Do not respond to specific antigens– Play essential auxiliary roles in immunity

Cells of the Adaptive Immune System


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• Immature lymphocytes released from bone marrow are essentially identical

• Whether a lymphocyte matures into a B cell or a T cell depends on where in the body it becomes Immunocompetent– B cells mature in the bone marrow– T cells mature in the thymus

Lymphocytes


T-lymphocytes: (Cell-mediated immunity)

• These are processed by the thymus gland, which lies between the heart and the sternum.

• The hormone thymosin, produced by the thymus, is responsible for promoting the processing, which leads to the formation of fully specialised (differentiated), mature, functional T-lymphocytes.

• A mature T-lymphocyte has been programmed to recognise only one type of antigen, and during its subsequent travels through the body will react to no other antigen, however dangerous it might be. Thus, a T-lymphocyte manufactured to recognise the chickenpox virus will not react to a measles virus,a cancer cell, or a tuberculosis bacterium.


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B-lymphocytes.

• These are processed in the bone marrow. Their role is in production of antibodies (immunoglobulins), which are proteins designed to bind to, and cause the destruction of, an antigen.

• As with T-lymphocytes,each B-lymphocyte targets one specific antigen; the antibody released reacts with one type of antigen and no other.


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• Display a unique type of receptor that responds to a distinct antigen.

• Become immunocompetent before they encounter antigens.

• Are exported to secondary lymphoid tissue where encounters with antigens occur.

• Mature into fully functional antigen-activated cells upon binding with their recognized antigen.

Immunocompetent B or T cells


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Red bone marrow

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2

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Immunocompetent, but still naive, lymphocyte migrates via blood

Mature (antigen-activated) immunocompetent lymphocytes circulate continuously in the bloodstream and lymph and throughout the lymphoid organs of the body.

Key: = Site of lymphocyte origin= Site of development of

immunocompetence as B or T cells; primary lymphoid organs

= Site of antigen challenge and final differentiation to activated B and T cells

Immature lymphocytes

Circulation in blood 1

1 Lymphocytes destined to become T cells migrate to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow.

ThymusBone

marrow

Lymph nodes, spleen, and other lymphoid tissues

2 2 After leaving the thymus or bone marrow as naive immunocompetent cells, lymphocytes “seed” the lymph nodes, spleen, and other lymphoid tissues where the antigen challenge occurs.

3 3

Activated immunocompetent B and T cells recirculate in blood and lymph

Immunocompetent B or T cells

Figure 21.8COMPILED BY: PROF.ANWAR BAIG (AIKTC,SOP)

Clonal expansion of T-Lymphocytes


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• Major roles in immunity are:– To engulf foreign particles– To present fragments of antigens on their

own surfaces, to be recognized by T cells• Major APCs are dendritic cells (DCs),

macrophages, and activated B cells• The major initiators of adaptive

immunity are DCs, which actively migrate to the lymph nodes and secondary lymphoid organs and present antigens to T and B cells

Antigen-Presenting Cells (APCs)


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• Antigen challenge – first encounter between an antigen and a naive immunocompetent cell

• Takes place in the spleen or other lymphoid organ

• If the lymphocyte is a B cell:– The challenging antigen provokes a

humoral immune response•Antibodies are produced against the challenger

Humoral Immunity Response


Clonal expansion of B-Lymphocytes


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Coordination of 2 immune system:


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• Stimulated B cell growth forms clones bearing the same antigen-specific receptors

• A naive, immunocompetent B cell is activated when antigens bind to its surface receptors and cross-link adjacent receptors

• Antigen binding is followed by receptor-mediated endocytosis of the cross-linked antigen-receptor complexes

• These activating events, plus T cell interactions, trigger clonal selection

Clonal Selection


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Clonal Selection


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• Most clone cells become antibody-secreting plasma cells

• Plasma cells secrete specific antibody at the rate of 2000 molecules per second

Fate of the Clones


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• Secreted antibodies:– Bind to free antigens– Mark the antigens for destruction by

specific or nonspecific mechanisms • Clones that do not become plasma

cells become memory cells that can mount an immediate response to subsequent exposures of the same antigen

Fate of the Clones


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• Primary immune response – cellular differentiation and proliferation, which occurs on the first exposure to a specific antigen– Lag period: 3 to 6 days after antigen

challenge– Peak levels of plasma antibody are

achieved in 10 days– Antibody levels then decline

Immunological Memory


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• Secondary immune response – re-exposure to the same antigen– Sensitized memory cells respond within

hours– Antibody levels peak in 2 to 3 days at

much higher levels than in the primary response

– Antibodies bind with greater affinity, and their levels in the blood can remain high for weeks to months

Immunological Memory


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Primary and Secondary Humoral Responses


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• B cells encounter antigens and produce antibodies against them– Naturally acquired – response to a

bacterial or viral infection– Artificially acquired – response to a

vaccine of dead or attenuated pathogens•Vaccines – spare us the symptoms of disease,

and their weakened antigens provide antigenic determinants that are immunogenic and reactive

Active Humoral Immunity


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• Differs from active immunity in the antibody source and the degree of protection– B cells are not challenged by antigens– Immunological memory does not occur– Protection ends when antigens naturally

degrade in the body• Naturally acquired – from the mother

to her fetus via the placenta• Artificially acquired – from the injection

of serum, such as gamma globulin

Passive Humoral Immunity


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Types of Acquired Immunity


(AIKTC,SOP)

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• Also called immunoglobulins – Constitute the gamma globulin portion of

blood proteins– Are soluble proteins secreted by activated

B cells and plasma cells in response to an antigen

– Are capable of binding specifically with that antigen

• There are five classes of antibodies: IgD, IgM, IgG, IgA, and IgE

Antibodies


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• IgD – monomer attached to the surface of B cells, important in B cell activation

• IgM – pentamer released by plasma cells during the primary immune response

• IgG – monomer that is the most abundant and diverse antibody in primary and secondary response; crosses the placenta and confers passive immunity

• IgA – dimer that helps prevent attachment of pathogens to epithelial cell surfaces

• IgE – monomer that binds to mast cells and basophils, causing histamine release when activated

Classes of Antibodies


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• Consists of four looping polypeptide chains linked together with disulfide bonds– Two identical heavy (H) chains and two

identical light (L) chains• The four chains bound together form

an antibody monomer• Each chain has a variable (V) region at

one end and a constant (C) region at the other

• Variable regions of the heavy and light chains combine to form the antigen-binding site

Basic Antibody Structure


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Basic Antibody Structure

Figure 21.12a, bCOMPILED BY: PROF.ANWAR BAIG

(AIKTC,SOP)

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• Antibodies responding to different antigens have different V regions but the C region is the same for all antibodies in a given class

• C regions form the stem of the Y-shaped antibody and:– Determine the class of the antibody– Serve common functions in all antibodies– Dictate the cells and chemicals that the

antibody can bind to– Determine how the antibody class will function

in elimination of antigens

Antibody Structure


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• Plasma cells make over a billion different types of antibodies

• Each cell, however, only contains 100,000 genes that code for these polypeptides

• To code for this many antibodies, somatic recombination takes place– Gene segments are shuffled and combined in

different ways by each B cell as it becomes immunocompetent

– Information of the newly assembled genes is expressed as B cell receptors and as antibodies

Mechanisms of Antibody Diversity


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• Random mixing of gene segments makes unique antibody genes that: – Code for H and L chains – Account for part of the variability in

antibodies• V gene segments, called hypervariable

regions, mutate and increase antibody variation

• Plasma cells can switch H chains, making two or more classes with the same V region

Antibody Diversity


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• Antibodies themselves do not destroy antigen; they inactivate and tag it for destruction

• All antibodies form an antigen-antibody (immune) complex

• Defensive mechanisms used by antibodies are neutralization, agglutination, precipitation, and complement fixation

Antibody Targets


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• Complement fixation is the main mechanism used against cellular antigens

• Antibodies bound to cells change shape and expose complement binding sites

• This triggers complement fixation and cell lysis• Complement activation:

– Enhances the inflammatory response– Uses a positive feedback cycle to promote

phagocytosis– Enlists more and more defensive elements

Complement Fixation and Activation


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• Neutralization – antibodies bind to and block specific sites on viruses or exotoxins, thus preventing these antigens from binding to receptors on tissue cells

Other Mechanisms of Antibody Action


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• Agglutination – antibodies bind the same determinant on more than one antigen – Makes antigen-antibody complexes that

are cross-linked into large lattices– Cell-bound antigens are cross-linked,

causing clumping (agglutination) • Precipitation – soluble molecules are

cross-linked into large insoluble complexes

Other Mechanisms of Antibody Action


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Mechanisms of Antibody Action


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• Commercially prepared antibodies are used:– To provide passive immunity– In research, clinical testing, and treatment

of certain cancers• Monoclonal antibodies are pure

antibody preparations – Specific for a single antigenic determinant– Produced from descendents of a single cell

Monoclonal Antibodies


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• Hybridomas – cell hybrids made from a fusion of a tumor cell and a B cell – Have desirable properties of both parent

cells – indefinite proliferation as well as the ability to produce a single type of antibody

Monoclonal Antibodies


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• Since antibodies are useless against intracellular antigens, cell-mediated immunity is needed

• Two major populations of T cells mediate cellular immunity– CD4 cells (T4 cells) are primarily helper T cells

(TH) – CD8 cells (T8 cells) are cytotoxic T cells (TC)

that destroy cells harboring foreign antigens• Other types of T cells are:

– Suppressor T cells (TS)– Memory T cells

Cell-Mediated Immune Response


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Major Types of T Cells


(AIKTC,SOP)

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• Soluble antibodies– The simplest ammunition of the immune

response– Interact in extracellular environments such

as body secretions, tissue fluid, blood, and lymph

Importance of Humoral Response


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• T cells recognize and respond only to processed fragments of antigen displayed on the surface of body cells

• T cells are best suited for cell-to-cell interactions, and target:– Cells infected with viruses, bacteria, or

intracellular parasites– Abnormal or cancerous cells– Cells of infused or transplanted foreign

tissue

Importance of Cellular Response


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• Immunocompetent T cells are activated when the V regions of their surface receptors bind to a recognized antigen

• T cells must simultaneously recognize:– Nonself (the antigen)– Self (a MHC protein of a body cell)

Antigen Recognition and MHC Restriction


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• Both types of MHC proteins are important to T cell activation

• Class I MHC proteins– Always recognized by CD8 T cells– Display peptides from endogenous

antigens

MHC Proteins


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• Endogenous antigens are:– Degraded by proteases and enter the

endoplasmic reticulum– Transported via TAP (transporter

associated with antigen processing)– Loaded onto class I MHC molecules– Displayed on the cell surface in

association with a class I MHC molecule

Class I MHC Proteins


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Class I MHC Proteins

Figure 21.15aCOMPILED BY: PROF.ANWAR BAIG

(AIKTC,SOP)

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• Class II MHC proteins are found only on mature B cells, some T cells, and antigen-presenting cells

• A phagosome containing pathogens (with exogenous antigens) merges with a lysosome

• Invariant protein prevents class II MHC proteins from binding to peptides in the endoplasmic reticulum

Class II MHC Proteins


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• Class II MHC proteins migrate into the phagosomes where the antigen is degraded and the invariant chain is removed for peptide loading

• Loaded Class II MHC molecules then migrate to the cell membrane and display antigenic peptide for recognition by CD4 cells



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Figure 21.15bCOMPILED BY: PROF.ANWAR BAIG (AIKTC,SOP)

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• Provides the key for the immune system to recognize the presence of intracellular microorganisms

• MHC proteins are ignored by T cells if they are complexed with self protein fragments

Antigen Recognition


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• If MHC proteins are complexed with endogenous or exogenous antigenic peptides, they:– Indicate the presence of intracellular

infectious microorganisms– Act as antigen holders– Form the self part of the self-antiself

complexes recognized by T cells

Antigen Recognition


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• T cell antigen receptors (TCRs):– Bind to an antigen-MHC protein complex – Have variable and constant regions

consisting of two chains (alpha and beta)

T Cell Activation: Step One – Antigen Binding


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• MHC restriction – TH and TC bind to different classes of MHC proteins

• TH cells bind to antigen linked to class II MHC proteins

• Mobile APCs (Langerhans’ cells) quickly alert the body to the presence of antigen by migrating to the lymph nodes and presenting antigen



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• TC cells are activated by antigen fragments complexed with class I MHC proteins

• APCs produce co-stimulatory molecules that are required for TC activation

• TCR that acts to recognize the self-antiself complex is linked to multiple intracellular signaling pathways

• Other T cell surface proteins are involved in antigen binding (e.g., CD4 and CD8 help maintain coupling during antigen recognition)



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(AIKTC,SOP)

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• Before a T cell can undergo clonal expansion, it must recognize one or more co-stimulatory signals

• This recognition may require binding to other surface receptors on an APC– Macrophages produce surface B7 proteins

when nonspecific defenses are mobilized– B7 binding with the CD28 receptor on the

surface of T cells is a crucial co-stimulatory signal

• Other co-stimulatory signals include cytokines and interleukin 1 and 2

T Cell Activation: Step Two – Co-stimulation


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• Depending on receptor type, co-stimulators can cause T cells to complete their activation or abort activation

• Without co-stimulation, T cells:– Become tolerant to that antigen– Are unable to divide – Do not secrete cytokines



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• T cells that are activated:– Enlarge, proliferate, and form clones– Differentiate and perform functions

according to their T cell class



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• Primary T cell response peaks within a week after signal exposure

• T cells then undergo apoptosis between days 7 and 30

• Effector activity wanes as the amount of antigen declines

• The disposal of activated effector cells is a protective mechanism for the body

• Memory T cells remain and mediate secondary responses to the same antigen



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• Mediators involved in cellular immunity, including hormonelike glycoproteins released by activated T cells and macrophages

• Some are co-stimulators of T cells and T cell proliferation

• Interleukin 1 (IL-1) released by macrophages co-stimulates bound T cells to:– Release interleukin 2 (IL-2) – Synthesize more IL-2 receptors

Cytokines


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• IL-2 is a key growth factor, which sets up a positive feedback cycle that encourages activated T cells to divide– It is used therapeutically to enhance the

body’s defenses against cancer• Other cytokines amplify and regulate

immune and nonspecific responses

Cytokines


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• Examples include:– Perforin and lymphotoxin – cell toxins– Gamma interferon – enhances the killing

power of macrophages– Inflammatory factors

Cytokines


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• Regulatory cells that play a central role in the adaptive immune response

• Once primed by APC presentation of antigen, they:– Chemically or directly stimulate

proliferation of other T cells– Stimulate B cells that have already

become bound to antigen• Without TH, there is no immune

response

Helper T Cells (TH)


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Helper T Cells (TH)

Figure 21.17aCOMPILED BY: PROF.ANWAR BAIG

(AIKTC,SOP)

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• TH cells interact directly with B cells that have antigen fragments on their surfaces bound to MHC II receptors

• TH cells stimulate B cells to divide more rapidly and begin antibody formation

• B cells may be activated without TH cells by binding to T cell–independent antigens

• Most antigens, however, require TH co-stimulation to activate B cells

• Cytokines released by TH amplify nonspecific defenses

Helper T Cell


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Helper T Cells

Figure 21.17bCOMPILED BY: PROF.ANWAR BAIG

(AIKTC,SOP)

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• TC cells, or killer T cells, are the only T cells that can directly attack and kill other cells

• They circulate throughout the body in search of body cells that display the antigen to which they have been sensitized

• Their targets include:– Virus-infected cells– Cells with intracellular bacteria or parasites– Cancer cells– Foreign cells from blood transfusions or

transplants

Cytotoxic T Cell (Tc)


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• Bind to self-antiself complexes on all body cells

• Infected or abnormal cells can be destroyed as long as appropriate antigen and co-stimulatory stimuli (e.g., IL-2) are present

• Natural killer cells activate their killing machinery when they bind to MICA receptor

• MICA receptor – MHC-related cell surface protein in cancer cells, virus-infected cells, and cells of transplanted organs

Cytotoxic T Cells


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• In some cases, TC cells:– Bind to the target cell and release perforin

into its membrane• In the presence of Ca2+ perforin causes cell

lysis by creating transmembrane pores• Other TC cells induce cell death by:

– Secreting lymphotoxin, which fragments the target cell’s DNA

– Secreting gamma interferon, which stimulates phagocytosis by macrophages

Mechanisms of Tc Action


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Mechanisms of Tc Action

Figure 21.18a, bCOMPILED BY: PROF.ANWAR BAIG (AIKTC,SOP)

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• Suppressor T cells (TS) – regulatory cells that release cytokines, which suppress the activity of both T cells and B cells

• Gamma delta T cells (Tgd) – 10% of all T cells found in the intestines that are triggered by binding to MICA receptors

Other T Cells


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Summary of the Primary Immune Response


(AIKTC,SOP)

Blood group

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AnaemiasIn anaemia there is not enough haemoglobin available to carry sufficient oxygen from the lungs to supply the needs of the tissues. It occurs when the rate of production of mature cells entering the blood from the red bone marrow does not keep pace with the rate of haemolysis.

The classification of anaemia is based on the cause:1. Impaired erythrocyte production— iron deficiency— megaloblastic anaemias— hypoplastic anaemia2. Increased erythrocyte loss— haemolytic anaemias— normocytic anaemia.

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Signs and symptoms of anaemia:

Tachycardia

Palpitations (an awareness of the heartbeat)

Angina pectoris

Breathlessness on exertion

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1. Iron deficiency anaemia

This is the most common. The normal daily requirement of iron intake in men is

about 1 to 2 mg derived from meat and highly coloured vegetables. The normal daily requirement in women is 3 mg. The increase is necessary to compensate for loss of blood

during menstruation and to meet the needs of the growing fetus during pregnancy. Children, during their period of rapid growth, require more

than adults.The anaemia is regarded as severe when the haemoglobin

level is below 9 g/dl blood. It is caused by deficiency of iron in the bone marrow and

may be due to dietary deficiency,excessively high requirement or malabsorption.

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2. Megaloblastic anaemias

1.Maturation of erythrocytes is impaired when deficiency of vitamin B12 and/or folic acid occurs and abnormally large erythrocytes (megaloblasts) are found in the blood.

2.During normal erythropoiesis several cell divisions occur and the daughter cells at each stage are smaller than the parent cell because there is not much time for cell enlargement between divisions.

3.When deficiency of vitamin B12 and/or folic acid occurs, the rate of DNA and RNA synthesis is reduced, delaying cell division.

4.The cells can therefore grow larger than normal between divisions. Circulating cells are immature, larger than normal and some are nucleated (MCV >94 fl).

5.The haemoglobin content of each cell is normal or raised. The cells are fragile and their life span is reduced to between 40 and 50 days.

6.Depressed production and early lysis cause anaemia.

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3.Hypoplastic and aplastic anaemias

i. Due to varying degrees of bone marrow failure. Bone marrow function is reduced in hypoplastic anaemia, and absent in aplastic anaemia.

ii. Since the bone marrow produces leukocytes and platelets as well as erythrocytes, leukopenia (low white cell count) and thrombocytopenia (low platelet count) are likely to accompany diminished red cell numbers.

iii.When all three cell types are low, the condition is called pancytopenia, and is accompanied by anaemia, diminished immunity and a tendency to bleed.

iv. The condition is often idiopathic.

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Known causes include:

• Drugs, e.g. cytotoxic drugs, some anti-inflammatory and

anticonvulsant drugs, some sulphonamides and antibiotics

• Ionising radiation

• Some chemicals, e.g. benzene and its derivatives

• Diseases : Chronic nephritis,Viral disease, including

hepatitis

• Invasion of bone marrow by, e.g., malignant disease,

leukaemia or fibrosis.

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4. Vitamin B12 deficiency anaemia

a. Pernicious anaemia

This is the most common form of vitamin B12 deficiency

anaemia.

It occurs more often in females than males, usually between 45

and 65 years of age.

It is an autoimmune disease in which auto-antibodies destroy

intrinsic factor (IF) and parietal cells in the stomach.

b. Dietary deficiency of vitamin B12

This is rare, when no animal products are included in the diet. The store of vitamin B12 is such that deficiency takes several years to appear.

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Other causes of vitamin B12 deficiencyi. Gastrectomy — this leaves fewer cells available to produce IF after partial resection of the stomach.

ii. Chronic gastritis, malignant disease and ionising radiation — these damage the gastric mucosa including the parietal cells that produce IF.

iii. Blind loop syndrome — this occurs when the contents of the small intestine are slow moving or static, allowing microbes to colonise the small intestine and use or destroy the intrinsic factor-vitamin B12 (IF-B12) complex before it reaches the terminal ileum where it is absorbed.

iv. Malabsorption of intrinsic factor-vitamin B12 complex — This may follow resection of terminal ileum or inflammation of the terminal ileum, e.g. Crohn's disease .

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Complications of vitamin B12 deficiency anaemia

These may appear before the signs of anaemia. They include:

• Subacute combined degeneration of the spinal cord in

which nerve fibres in the posterior and lateral columns of white matter become demyelinated.

(Vitamin B12 is essential for the secretion and maintenance of myelin.)

• Ulceration of the tongue and glossitis.

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Haemolytic anaemias

These occur when red cells are destroyed while in circulation or are removed prematurely from the circulation because the cells are abnormal or the spleen is overactive.1.Congenital haemolytic anaemias:

Sickle cell anaemiaThalassaemiaHaemolytic disease of the newborn

2. Acquired haemolytic anaemiaChemical agentsAutoimmunityBlood transfusion reactionsOther causes of haemolytic anaemia

eg: Parasitic diseases, e.g. malariaIonising radiation, e.g. X-rays, radioactive isotopesDestruction of blood trapped in tissues in, e.g., severe burns, crushing injuriesPhysical damage to cells by, e.g., artificial heart valves, kidney

dialysis machines.

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Normocytic normochromic anaemia

1.In this type the cells are normal but the numbers are

reduced.

2.The proportion of reticulocytes in the blood may be

increased as the body tries to restore erythrocyte numbers

to normal.

3.This occurs:

• In many chronic disease conditions, e.g. in chronic

inflammation following severe haemorrhage in

haemolytic disease.

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Congenital haemolytic anaemiasIn these diseases genetic abnormality leads to the synthesis of abnormal haemoglobin and increased red cell membrane friability, reducing cell oxygen-carrying capacity and life span. The most common forms are sickle cell anaemia and thalassaemia.

a. Sickle cell anaemia:1.The abnormal haemoglobin molecules become misshapen.2.When deoxygenated, making the erythrocytes sickle shaped. 3.A high proportion of abnormal molecules makes the sickling permanent. 4.The life span of cells is reduced by early haemolysis. 5.Sickle cells do not move smoothly through the small blood vessels. 6.This tends to increase the viscosity of the blood, reducing the rate of blood flow and leading to intravascular clotting,ischaemia and infarction. 7.The anaemia is due to early haemolysis of irreversibly sickled cells.8.Blacks are more affected than other races. 9.Some affected individuals have a degree of immunity to malaria because the life span of the sickled cells is less than the time needed for the malaria parasite to mature inside the cells.

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b. Thalassaemia

There is reduced globin synthesis with resultant reduced haemoglobin production and increased friability of the cell membrane, leading to early haemolysis.

Severe cases may cause death in infants or young children. This condition is most common in Mediterranean countries.

Haemolytic disease of the newbornIn this disorder, the mother's immune system makes antibodies to the baby's red blood cells, causing haemolysis and phagocytosis of fetal erythrocytes. The antigen system involved is usually (but not always) the Rhesus (Rh) antigen.

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PolycythaemiaThere are an abnormally large number of erythrocytes in the blood. This increases blood viscosity, slows the rate of flow and increases the risk of intravascular clotting, ischaemia and infarction.

i. Relative increase in erythrocyte count:This occurs when the erythrocyte count is normal but the blood volume is reduced by fluid loss, e.g. excessive serum exudate from extensive superficial burns.

ii. True increase in erythrocyte count Physiological. Prolonged hypoxia stimulates erythropoiesis and the number of cells released into the normal volume of blood is increased.

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Ø This occurs in people living at high altitudes where the oxygen tension in the air is low and the partial pressure of oxygen in the alveoli of the lungs is correspondingly low. Ø Each cell carries less oxygen so more cells are needed to meet the body's oxygen needs

a. Polycythaemia Pathological.

The reason for this increase in circulating red cells, sometimes to twice the normal number, is not known. It may be secondary to other factors that cause

Hypoxia of the red bone marrow, e.g. cigarette smoking,pulmonary disease, bone marrow cancer..

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b. Polycythaemia rubra veraIn this primary condition of unknown cause there is

abnormal excessive production of the erythrocyte precursors, i.e.myeloproliferation.

This raises the haemoglobin level and the haematocrit (relative proportion of cells to plasma).

The blood viscosity is increased and may lead to hypertension and cerebral, coronary or mesenteric thrombosis.

Aplastic anaemia and leukaemia may also be present.

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LEUKOCYTE DISORDERS• Leukopenia --Granulocytopenia (neutropenia)• Leukocytosis• Leukaemia

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1.Leukopenia

This is the name of the condition in which the total blood leukocyte count is less than 4000/mm3.a. Granulocytopenia (neutropenia)i. This is a general term used to indicate an abnormal reduction in the numbers of circulating granulocytes (polymorphonuclear leukocytes), commonly called neutropenia because 40 to 75% of granulocytes areneutrophils. ii. A reduction in the number of circulating granulocytes occurs when production does not keep pace with the normal removal of cells or when the life span of the cells is reduced.iii. Extreme shortage or the absence of granulocytes is called agranulocytosis. A temporary reduction occurs in response to inflammation but the numbers are usually quickly restored.

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Inadequate granulopoiesis may be caused by:1. Drugs, e.g. cytotoxic drugs, phenylbutazone, phenothiazines,

some sulphonamides and antibiotics2. Irradiation damage to granulocyte precursors in the bone marrow

by, e.g., X-rays, radioactive isotopes3. Diseases of red bone marrow, e.g. leukaemias, some anaemias4. Severe microbial infections.5. In conditions where the spleen is enlarged, excessive numbers of

granulocytes are trapped, reducing the number in circulation.

Neutropenia predisposes to severe infections that can lead to tissue necrosis, septicaemia and death. Septicaemia is the presence of significant numbers of active pathogens in the blood. The pathogens are commonly commensals, i.e. microbes that are normally present in the body but do not usually cause infection,

such as those in the bowel.

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Leukocytosisi. An increase in the number of circulating leukocytes

occurs as a normal protective reaction in a variety of pathological conditions, especially in response to infections.

ii. When the infection subsides the leukocyte count returns to normal.

iii.Pathological leukocytosis exists when a blood leukocyte count of more than 11000/mm3 is sustained and is not consistent with the normal protective function.

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Leukaemia•Leukaemia is a malignant proliferation of white blood cell precursors by the bone marrow. •A malignant progressive disease in which the bone marrow and other blood-forming organs produce increased numbers of immature or abnormal leucocytes. These suppress the production of normal blood cells, leading to anaemia and other symptoms.•It results in the uncontrolled reduction of leukocytes and/or their precursors. •As the tumour cells enter the blood the total leukocyte count is usually raised but in some cases it may be normal or even low. •The proliferation of immature leukaemic blast cells crowds out other blood cells formed in bone marrow, causing anaemia,thrombocytopenia and leukopenia (pancytopenia).

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Causes of leukaemiaIonising radiation. Radiation such as that produced by X-rays and radioactive isotopes causes malignant changes in the precursors of white blood cells. The DNA of the cells may be damaged and some cells die while others reproduce at an abnormally rapid rate. Leukaemia may develop at any time after irradiation, even 20 or more years later.Chemicals. Some chemicals encountered in the general or work environment alter the DNA of the white cell precursors in the bone marrow. These include benzene and its derivatives, asbestos, cytotoxic drugs, chloramphenicol.Viral infections.Genetic factors. Identical twins of leukaemia sufferers have a much higher risk than normal of developing the disease, suggesting involvement of genetic factors.

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Types of leukaemias

Acute leukaemiasØ These types usually have a sudden onset and affect the poorly differentiated and immature 'blast' cells .Ø They are aggressive tumours that reach a climax within a few weeks or months. The rapid progress of bone marrow invasion impairs its function and culminates in anaemia, haemorrhage and susceptibility to infection.Ø The mucous membranes of the mouth and upper gastrointestinal tract are most commonly affected.Acute myeloblastic leukaemia. This occurs at any age, but most commonly between 25 and 60 years.Acute lymphoblastic leukaemia. This disease is most common in children under 10 years, although a number of cases may occur up to about 40 years of age.

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Chronic leukaemiasThese conditions are less aggressive than the acute forms and the leukocytes are more differentiated, i.e. at the 'cyte' stage.Chronic granulocytic leukaemia. There is a gradual increase in the number of immature granulocytes in the blood. In the later stages, anaemia, secondary haemorrhages, infections and fever become increasingly severe. It is slightly more common in men than women and usually occurs between the ages of 20 and 40 years. Although treatment may appear to be successful, death usually occurs within about 5 years.Chronic lymphocytic leukaemia. There is enlargement of the lymph nodes and hyperplasia of lymphoid tissue throughout the body. The lymphocyte count is considerably higher than normal. Lymphocytes accumulate in the bone marrow and there is progressive anaemia and thrombocytopenia. It is three times more common in males than females and it occurs mainly between the ages of 50 and 70 years. Death is usually due to repeated infections of increasing severity, with great variations in survival times.

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ThrombocytopeniaThis is defined as a blood platelet count below (150 000/mm3) but spontaneous capillary bleeding does not usually occur unless the count falls below (30 000/mm3). It may be due to a reduced rate of platelet production or increased rate of destruction.Reduced platelet productionThis is usually due to bone marrow deficiencies, and therefore production of erythrocytes and leukocytes is also reduced, giving rise to pancytopenia. It is often due to:Ø Platelets being crowded out of the bone marrow in bone marrow diseases, e.g. leukaemias, pernicious anaemia, malignant tumoursØ Ionising radiation, e.g. X-rays or radioactive isotopes,that damage the rapidly dividing precursor cells in the bone marrowØDrugs, e.g. cytotoxic drugs, chloramphenicol,chlorpromazine, phenylbutazone, sulphonamides.Increased platelet destruction A reduced platelet count occurs when production of new cells does not keep pace with destruction of damaged and worn out cells.

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Autoimmune thrombocytopenic purpura.• This condition, which usually affects children and young

adults,• may be triggered by a viral infection such as measles.• Antiplatelet antibodies are formed that coat platelets,• leading to platelet destruction and their removal from• the circulation. • A significant feature of this disease is the presence of

purpura, which are haemorrhages into the skin ranging in size from pinpoints to large blotches.

• The severity of the disease varies from mild bleeding into• the skin to severe haemorrhage. When the platelet count• is very low there may be severe bruising, haematuria,• gastrointestinal or cranial haemorrhages.

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Secondary thrombocytopenic purpura. This may occur in association with red bone marrow diseases,excessive irradiation and some drugs, e.g. digoxin,chlorthiazides, quinine, sulphonamides.

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Education

5. Haematology