Chapter 24 ~ The Immune System

Animal immune system

Phagocytic and Natural Killer Cells• Neutrophils

60-70% WBCs; engulf and destroy microbes at infected tissue

• Macrophages

enzymatically destroy microbes

• Natural killer (NK) cells

destroy virus-infected body cells & abnormal cells

The Inflammatory Response • Histamine triggers dilation and permeability of capallarie

• Chemokines: attract phagocytes• Leukocyte-released molecules increase body temperature

The lymphatic system• Involved in innate and acquired immunity.

• Functions are to return fluid from the interstitial spaces to the circulatory system, and to combat infection

Acquired Immunity• Antigen: a foreign molecule that elicits a

response by lymphocytes (virus, bacteria, fungus, protozoa, parasitic worms)

• Antibodies: antigen-binding immunoglobulin, produced by B cells.

• Vaccine : introduction of a harmless variant to stimulate immune system.

• Active immunity: immune system produces antibodies.

• Passive immunity: receiving pre-made antibodies.

Lymphocyte’s dual defense• Types of lymphocytes: B cells develop in

bone marrow, T cells develop in the thymus.

• Humoral immune response is the production of antibodies by B cells. Defend against bacteria and viruses found in body fluids.

• Cell mediated immune response is the production of defensive cells by T cells- phagocytes.

Clonal selection

• Clonal selection: antigen-driven cloning of lymphocytes

• Effector cells: short-lived cells that combat the antigen that secrete antibodies

• Memory cells: long-lived cells that bear receptors for the antigen

Immune Responses• Primary immune response: lymphocyte proliferation and

differentiation the 1st time the body is exposed to an antigen

• Plasma cells: antibody-producing effector B-cells

• Secondary immune response: immune response if the individual

is exposed to the same antigen at some later time~ Immunological memory

Antibodies (Ig)

• Two functions of antibodies: recognize and bind to antigens, and then to neutralize that antigen.

• The antigen binding site is shape specific for antigen.

• Antibodies mark specific antigens for destruction.

Helper T’s role in humoral and cell mediated responses

• Helper T cells release proteins that activate both cytotoxic T cells and B cells

Cytotoxic T cells destroy infected body cells

Summary of acquired immunity• Humoral immunity• B cell activation• Production of antibodies• Defend against bacteria,

toxins, and viruses free in the lymph and blood plasma

• Cell-mediated immunity• T cell activation• Binds to and/or lyses cells• Defend against cells infected

with bacteria, viruses, fungi, protozoa, and parasites; nonself interaction