Cutaneous Immunology

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CUTANEOUS IMMUNOLOGY

นพ.สุ�รสุฤษดิ์ ขาวละออ992009/ /

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CONTENTS

Normal skin structure Cutaneous immunology

-innate immunity-IL-1-complement activation-PRRs -Langerhans’ cell & dermal DC

-acquired immunity-role of T & B cell

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NORMAL SKIN STRUCTURE

Three functional layers-epidermis 150 µm thick

-horny layer-clear layer-granular layer-basal layer-basal membrane

-dermis or corium

2,800 µm thick

-subcutis

(hypodermis)

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1 Epidermis

2 Dermis

3 Subcutis

4 Hair follicle

5 Sebaceous gland

6 Sweat gland

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NORMAL SKIN STRUCTURE1 Horny layer

(stratum corneum)2 Clear layer

(stratum lucidum)3 Granular layer

(stratum granulosum)4 Prickle-cell layer

(stratum spinosum)5 Basal layer

(stratum basale)6 Basal membrane

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Dendritic cells in cutaneous immunity

The Langerhans’ cells(epidermal DC)-LC arise in BM-controversy about whether LC descended from myeloid or lymphoid progenitor but evidence suggest myeloid origin

Carole L. Berger.IJBCB 2006;38:1632-1636

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The Langerhans’ cells(cont.)-can differentiate from monocytes or CD34 precursors(CD34=precursors of hemopoietic cells/endothelium in high endothelial venules)

-mediators of LC differentiation from peripheral monocytes include TGF-β, GM-CSF, IL-4 and Notch ligand δ-1


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The Langerhans’ cells(cont.)-keratinocyte secrete TGF-β, GM-CSF and δ-1-LC express CCR6 Rc for MIP-3α

(CCL20) by keratinocytes-LC that endocytosed Ag and be activated by inducible innate response may directly present Ag to skin-resident memory T cells or exit skin via lymph vessels

N Franklin. Middleton’s allergy 7th edition 2009

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The Langerhans’ cells(cont.)-in LNLC process and present Ag peptide to naïve T cells initial step to develop acquired immunity-LC can induce tolerance to self-Ag if take up apoptotic material through stimulation of T-regulatory cells which inhibit immune responses


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Dermal dendritic cellstwo types of DDC

1.interstitial DDC-dermis compose of extracellular matrix (ECM) and contain fibroblasts,DC,MØ, infiltrating T lymphocytes-dermal DC present in ECM & also called type-I dendrocytes

J.Valladeau.Seminars in Immunology 2005;17:273-283

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Dermal dendritic cells(cont.)-expression MHC class II, scavengerRc (CD36), coagulation factor XIIIa these 3 markers can find in MØ-expression of lectin DC-SIGN/CD209 distinguishes DDC from other dermal cellular populations


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Dermal dendritic cells(cont.)2.plasmacytoid DC-pDC lymphoid origin-natural IFN-/-producing cells-present in skin in atopic dermatitis, contact dermatitis, psoriasis, SLE-immature pDC also described in situ in primary melanoma-normal skinvery low frequency


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Dermal dendritic cells(cont.) plasmacytoid DC(cont.)-more sensitive than myeloid skin DC to danger signals produce typeI-IFN via TLRs-little is know about pDC trafficking in vivo


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Dermal dendritic cells(cont.) plasmacytoid DC(cont.)-mechanism for recruitment into skin1.1.pDC express CCR6(Rc of CCL20 that responsible for homing of LC to skin1.2.pDC express CXCR3 whose ligrands highly expressed in inflammatory skin1.3.pDC express ChemR23 binds chemerinexpressed on dermal inflamed vessels


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Migration of cutaneous DCs1.TNF- & IL-1 induce migration of LC out of epidermis2.CCR6 control migration from blood/dermis to epidermis3.CCR7 control migration from epidermis to regional lymphatics (CCR7=Rc of SLC)


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Migration of cutaneous DCs(cont.)4.trafficking is controlled at level of cell adhesion

-LC down-regulate some adhesion molecules to exis epidermis and up-regulate other to migrate across dermal ECM & home to T cell area of region lymphoid tissue


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Migration of cutaneous DCs(cont.)-key role of CD44 & 6 integrins in LC migration was demonstrate-down-regulation of E-cadherin also key event in LC migration

5.expression of matrix metalloproteinases-9 & -2 (MMP) are necessary both for

migration of LC & DDC


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-cutaneous DC Ag presentation involve interaction of

-MHC class II-antigenic pepetide-MHC class I-antigenic peptide-via CD1 molecules(non-peptide microbial antigen presented)


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Epidermis lymphocyte-about 1% in epidermis-close proximity to basement membrane-majority of T cells are memory cell (CD45RO+) most express CD8 receptor-50% of epidermal T cell express CLA (cutaneous lymphocyte Ag) : Sialyl Lewis-X glycoprotein serve as ligand to endothelial cell adhesin (E-selectin)

B.Spellberg.Life Sciences 2000;67:477-502

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Epidermis lymphocyte(cont.)-T cell do not enter epidermis by random migration, rather epidermal T cells are special population of memory cells, which have specific set of instruction to selectively home to epidermis-human αβ-T cell : γδ-T cell = 10:1


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Nerve-numerous free nerve endings, consist of dendrite branching of slow conducting nerve fibers-afferent sensory, unmyelinated, terminate at epidermal surface of basement membrane


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Nerve(cont.)-nerve ending can be found between keratinocytes through Stratum Granulosum -able to elaborate neuropeptides which modulate local immunologic function


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INNATE IMMUNITY


keratinocyte express epidermal growth factors : amphiregulin

-induce inflammatory-immune reaction-recent finding expression amphiregulin by Th2 important mechanism to clear intestinal helminth infestation through epithelial shedding

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INNATE IMMUNITY

epidermal γδ-T cells, like B cell, capable directly binding to small phospate containing Ag with their receptors-do not require Ag presentation in context of MHC or CD1-serve as primitive, immediate response element, recognizing conserved phosphoprotein or phospholipid Ag of microbes & necrotic human tissues


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Innate immunity-first-line defense mechanism-two separate categories

-constitutive innate immunity-anatomic barrier

-physiologic barrier


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-inducible innate immunity-acute inflammation-cellular infiltration

-both do not demonstrates acquired specificity or memory for invading pathogen


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INNATE IMMUNITY

1.cutaneous constitutive innate immunity consist of

1.1.normal skin flora1.2.cornified keratinocytes1.3.antimicrobial polypeptides/lipids1.4.low pH1.5.normal body temperature


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INNATE IMMUNITY

Normal flora of skin-coryneforms and staphylococci -mush lesser extent, fungi (primarily Malassezia)

Compete with other pathogenic organisms


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INNATE IMMUNITY

Cornified keratinocytes -form impenetrable surface-outward growth and shedding of cornified keratinocytes eliminate superficially bound pathogens-reduced water content & lipid layers of stratum corneum reduce relative humiditybad environment


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INNATE IMMUNITY

Antimicrobial polypeptides -β-defensin-1 and -2, dermcidin, iron-binding proteins, lysozyme, RNases, DNases, and natural IgM on skin from sweat and from keratinocytes

Reduce skin surface pH-exhibit antibacterial activity-lactic acid excreted in eccrine sweat


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INNATE IMMUNITY

Normal body temperature -inhibits growth of some pathogens

2.Inducible innate immunityAcute inflammation2.1.performed IL-1α stored in cytoplasm of keratinocyte,released from

itch/scratch2.2.TNF-α


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INNATE IMMUNITY

IL-1-2 forms : α and β-31 kDa molecules-IL-1β must be cleaved by ICE

(IL-1β converting enzyme : caspase-1)-produced by monocyte, MØ, langerhans cells, dendritic cells

-IL-1α biologically active predominates in epithelial cells (keratinocytes, etc)

Murphy JE. J Invest Dermatol 2000; 114:602-608

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INNATE IMMUNITY

-receptors-IL-1R1 can bind both IL-1α & IL-1β-IL-1ra(IL-1 receptor antagonist) bind to this Rc but does not induce signaling

-mice defcient in IL-1ra show exaggerated & persistent inflammatory responses


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INNATE IMMUNITY

-IL-1R2 -short cytoplasmic domain -bind IL-1α & IL-1β efficiently-but not IL-1ra-serves to inhibit IL-1 responses-expression can be upregulated by corticosteroids & IL-4


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INNATE IMMUNITY


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INNATE IMMUNITY


-important among this cascade of events is induced expression inflammatory cytokine, chemokine, mediators(eicosanoids, histamine, neuropeptides, ROS)-contribute to classic signs of acute inflammation : redness, heat, swelling, pain

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INNATE IMMUNITY


IL-1α induce molecules of typical cutaneous inflammatory response include : TNF-α, IL-8(CXCL-8),

nitrous oxide synthase, PG-producing cyclooxygenase, postcapillary venule endothelial cell expression of ICAM-1, VCAM-1, E-seletin

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INNATE IMMUNITY


-Moreover,IL-1α & other induced molecules activate most cell types of skin, alerting and preparing them for further host defense functions including cytokine and chemokine secretion, wound repair, release of antimicrobial products, phagocytosis, initiation of acquired immune responses

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INNATE IMMUNITY


2.3.inducible pathogen-targeted soluble

molecules

-inducible antimicrobial polypeptides

-complement-activating a/o opsonin

proteins

-complement proteins

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INNATE IMMUNITY


Inducible antimicrobial polypeptides

-β-defensin-2 and -3, cathelicidin LL-37

-produced by keratinocytes

-IFN-α, IFN-β, IFN-k another class of

antimicrobial polypeptides

(IFN-α produced by plasmacytoid DC,

mononuclear phagocytes)

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INNATE IMMUNITY


-IFN-β produced by many cell ; fibroblasts

sometimes called fibroblasts IFN)

-protective activities related to antiviral

effect on host cells rather than diract toxic

to pathogen

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INNATE IMMUNITY


2.4.complement activating/opsonin molecules-members of acute phase proteins (C-reactive protein, serum amyloid protein)-members of collectin(mannan-binding lectin)-ficolin lectin families-C3b fragment, natural IgM

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INNATE IMMUNITY


2.4.complement activating/opsonin molecules-acute phase protein produced by liver & supply to skin via blood-increase serum concentration in response to IL-1, IL-6, TNF-α from activated MØ-collectins & ficolins recognize carbohydrates on bacteria, fungi, viruses then mark them for destruction

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INNATE IMMUNITY


-opsonin C3b target pathogen : phagocytosis

-C3a, C5a(anaphylatoxins) : keratinocyte

activating, chemoattractant, mast cell

degranulating functions)

-C5b, C6, C7, C8, C9 : MAC(lethal pore)

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INNATE IMMUNITY


2.5.PRRs host molecules recognize -PRRs host molecules recognize PAMPs -PAMPs include

-unmethylated CpGs of bact. DNA-dsRNA(e.g.influenza)-mannans-gram+ bact. lipoteichoic acids-gram- bact. LPS-bacterial peptidoglycan

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INNATE IMMUNITY

2.5.PRRs host molecules recognize(cont.)-N-terminal formyl-methionine-parasitic phosphoglycans-fungal glucans/zymosan

-MØ & DC ,activated during cutaneous inflammatory response, first phagocytic host cells utilizing their cell-surface PRRs


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INNATE IMMUNITY

-inflammation-ass increase chemotactic factors (chemokines), produced by keratinocytes stimulated via their TLRs and postcapillary venule endothelial cell adhesion molecules (P- & E-selectin, ICAM-1, VCAM-1) synergiscally mediate integrin-dependent extravasation of PRR-expressing leukocytes


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INNATE IMMUNITY

-cellular infiltration -neutrophils earliest infiltrating leukocytes(due to neutrophil active CXC : IL-8)-later, monocyte begin extravasate into inflam. site-assist in phagocytosis & intracellular destruction of pathogen with lysozyme, defesins, ROI


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INNATE IMMUNITY

-eosinophil less phagocytic than neutrophil, produce ROS at plasma membrane surface, not intracellularly readily degranulate & deposit toxic cationic proteins onto surface of parasites-furthermore : basophils, blood Dc, mast cell, T cells, B cell, NK-T cell, NK cells


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INNATE IMMUNITY

-local defenses are quickly augmented by recruitment of dermal MØ, just beneath basement membrane-lymphocyte-/keratinocyte-derived IFN & growth factors across basement membrane initiates priming MØ to produce IL-12


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INNATE IMMUNITY

-epidermal-derived cytokine & Ag stimuli MØ mobilize their cytoskeletons to become mobile & secrete metalloproteinases and degradative enzymes allow them to slice through collagen and other structural components of basement membranecross into epidermis


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INNATE IMMUNITY

-MØ use ligands expressed on activated keratinocytes, such as E-cadherin/ICAM-1, to pull themselves through epidermis and crawl to danger site by following chemokine gradient to its source


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INNATE IMMUNITY


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INNATE IMMUNITY


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ACQUIRED IMMUNITY

-inflammation state that continues beyond 24-36 hr induces onset of adaptive immunity-IFN-γ in epidermis stimulates leukocytes, fibroblasts to express CC chemokines, particular MCP-1, MIP-1, RANTES while suppress production of CXC chemokines such as IL-8


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ACQUIRED IMMUNITY

-MIP-1α : CCL20;induce chemotaxis of

neutrophil and lymphocytes

-MCP-1 : chemotactic for monocytes

& lymphocytes

-RANRES : selectively pro-inflammatory

Th1 lymphocytes, not

inflammatory-suppressive

Th2 cellsB.Spellberg.Life Sciences 2000;67:477-502

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ACQUIRED IMMUNITY

-Th1 have RANTES Rc : CCR5

-Th1 produce IFN-γ which drive RANTES

production by lymphocytes and MØ selectively summon additional Th1 cells

to area of danger


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ACQUIRED IMMUNITY

-endothelial cell adhesins critical to

selection of leukocyte extravasation

-several hour after stimulationlower

their expression of E-selectin(CD62E),

upregulate their ICAM-1 expression,

begin express VCAMdiminish neutrophil

across vascular lumenL & Mo are

recruited into areaB.Spellberg.Life Sciences 2000;67:477-502

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ACQUIRED IMMUNITY

-exposure to IFN-γendothelium express

MHC class II

then presence of IFN-γ, microvascular

endothelial cells capable acting as

professional APC to circulating T cells


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ACQUIRED IMMUNITY

-In presence in skin of IFN-γ, IFN-α, TNF-α, microbial particles (LPS, gram+ cell wall fractions, prokaryotic DNA)induces MØ & DC produce IL-12-IL-12 induces newly activated T cell to Th1


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ACQUIRED IMMUNITY

-if stimulus initiating danger response is

too bulky(hyphal fungi, helminths, large

foreign bodies,etc)leukocytes initiate

“frutrated phagocyte complex” this

induce production of IL-10 prefentially

over IL-12favoring antibody-based Th2


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ACQUIRED IMMUNITY

-antibody production stimulated by Th2

response allow leukocytes to damage

large organisms via ADCC

-eosinophil, neutrophil, NK, monocyte/MØ

able to use this mechanism


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ACQUIRED IMMUNITY

-B cell other key cell for acquired immunity

-B cell recognize relatively intact Ag

(contrast T cells)

-plasma cell, memory B cell development,

Ig class switching, somatic hypermutation

all occur in secondary lymphoid geminal

center of skin-draining LN


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ACQUIRED IMMUNITY

-absence of cutaneous B cells suggests a

need for Ag that enter skin to be

transported to B cell as opposed to B cell’s

migrating to Ag in skin(but mechanism of

B cell activation remains unclear)

-five classes of Ig have been detected in

normal human sweat


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ACQUIRED IMMUNITY

-sIgA arise from secretory epithelia of eccrine glands, sebum also contain IgA-exact source of cutaneously secreted Ig remains unresolved-IgG1 & IgA capable to clear pathogenic organisms from skin via Fcγ Rc-mediated immune response(ADCC, complement fixation) and sIgA-coating of bacteria


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ACQUIRED IMMUNITY

-in human IgE & IgG4 produced by type 2

cytokine (IL-4, IL-13)

-most antigen-specific IgE supplied via

blood(except respiratory mucosa , local

IgE production appear posible)

-IgE can bind to FcεRI-bearing cells(LC,

mast cell, infiltrating basophils)contribute

to various allergic skin dzN Franklin. Middleton’s allergy 7th edition 2009

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ACQUIRED IMMUNITY

-Ab specific for FcεRI may contribute to

cutaneous dz such as urticaria, Ab against

desmosomal and hemidesmosomal protein

provoke immunobullous dz


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ACQUIRED IMMUNITY

-impact of innate to acquired immunity-chemotactic activity of β-defesin-2 & C5a for DC a/o T cells-tissue injury danger signals or engagement of PRRs(LPS Rc, mannose binding Rc, TLRs, CD1a) expressed on cutaneous APC such as Langerhans’ cells, dermal DC, MØ


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ACQUIRED IMMUNITY

increase co-stimulatory molecule expression (CD80 & CD86) & modulate

cytokine expression patterns-LPS bind to cell surface CD14 of MØ induces IL-12favor Th1 development-mast cell-produced cytokines such as IL-4, histamine, keratinocyte-derived thymic stromal lymphopoietin(TSLP)acquire immune response Th2 profile


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ACQUIRED IMMUNITY


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SUMMARY


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TAKE HOME MESSAGE

-Various constitutive and inducible innate immune mechanisms function in skin to fight infection and to direct acquired immunity – these include keratinocyte– derived molecules such as IL-1, antimicrobial peptides -Immune functions attributed to cutaneous mast cells and dendritic cells (DCs)

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TAKE HOME MESSAGE

-Langerhans' cells, dermal DCs, and DCs infiltrating during inflammatory disease are increasing in number and

being redefined-Skin homing of memory, effector, and regulatory T-cell subtypes is programmed by skin-derived DCs and prominently directed by CLA,other types of chemokines

Health & Medicine

Cutaneous Immunology