Immunology, Papworth Hospital, CambridgeAR Exley Mucosal Immune System Dr Andrew Exley Immunology Lab & Lung Defence Unit Papworth Hospital.

Immunology, Papworth Hospital, CambridgeAR Exley

Mucosal Immune System

Dr Andrew Exley

Immunology Lab & Lung Defence Unit

Papworth Hospital


Introduction

Mucosal DefenceMucosal Immune system

– Antigen - induced expansion of lymphoid tissue– Lymphocyte homing– Functional and phenotypic diversity– Regulatory T cells– Immunoglobulin IgA– Immunity thru’ Vaccination


Mucosal Defence

Direct interface with exterior

First line defences

Innate immunity

Antigen load - food, inhaled antigen, microbes– Germ-free animals


Mucosal Defence Mechanisms

Commensal bacteria Gastric Acid, Bile Mucous secretion Shedding of Epithelium Peristalsis Lactoferrin Lysozyme

Commensal bacteria?

Mucous secretion Mucociliary escalator Soluble factors

– Complement– Surfactant proteins– Defensins– Proteases

GI tract Respiratory tract


Mucosal Immune System

Immune response – Induction & Expression within same system

Mucosal Lymphocytes – Remain within the mucosal immune system– Lymphocyte migration / homing / retention

Special T cells– CD8 / , and regulatory T cells


Gut-associated Lymphoid Tisssue

Functional and phenotypical division Secondary lymphoid tissue

– Peyer’s patches, lymphoid follicles in gut wall» ~lymph nodes, for Ag uptake and presentation

– Draining lymph nodes » Mesenteric LNs

Non-lymphoid tissue– Lamina propria lymphocytes– Intra-epithelial lymphocytes


Intra-epithelial Lymphocytes

<20% of epithelial cells T cells Groh 1998

– NK receptor NKG2D versus MHC class I

– non-classical MHC class I MIC-A, MIC-B

– MIC-A/B upregulated by stress

– Deletion of damaged, aged, disordered epithelial cells

T cells CD8 /– extra-thymic development

– Role in humans?


Lamina propria Lymphocytes

T cells, B cells, macrophages, dendritic cellsCD4+ T cellsNaive CD45RA+ & memory CD45RO+ TTH2/TH3 cytokines dominant

– IL-4, IlL-5, IL-10, TGF-IgA switch factor)– Regulatory T cells!

TH1 cytokines non-dominant – IFN-, IL-2, IL-12, TNF-


Controlling the Immune Response in the GI tract

FoodProtection

Infection Pathogenic immunity

Bacteria driven Inflammatory Bowel disease– Adoptive transfer studies– Colitis : CD4+ CD45RBhigh

– Protection : CD4+ CD45RBlow CD25+ subset


CD4+ CD45RBlow CD25+ T cells

Naturally activated~10% of CD4+ T cellsUnresponsive in vitroInhibit wide range of immune responses

– To self– To pathogens Maloy 2003

Transcription factor Foxp3Effector function present in thymus


Regulatory T cells - natural

T cells from thymus / peripheral bloodClassical transfer experimentsCD4+ CD25+ T cells in mice inhibit

– autoimmune diabetes– inflammatory bowel disease– anti-tumour immunity– expansion of other T cells in vitro– Promote tolerance to skin allografts


Regulatory T cells - induced

Foxp3 transcription factor positive– Physiological inducers?– Trl IL10 producers– Tr3 TGF producers

» Inducible with TGF Chen 2003

– Inhibit Th1, Th2 responses in vivo Classical

– Ag delivered at mucosal sites induces peripheral + mucosal unresponsiveness Ostroukhova 2004

– Soluble Peptide induced tolerance» oral, nasal, peritoneal, subcutaneous, intradermal route» Peptides must be ~ naturally occurring epitopes


Oral Tolerance – Clinical Use?

Good data in autoimmune disease models – Prophylaxis prevents / attenuates disease

– Treatment suppresses disease

– Dose dependent effects

Poor results to date from studies of Clinical diseases– Monitor state & mode of oral tolerance induced

– Phase III: Oral MBP analogue in Multiple sclerosis

– NIH study: oral insulin in juvenile diabetes mellitus

– Myasthenia gravis : anti-ACHreceptor responses


Anti-CD3 mAb induced regulatory T cells?

Intervention in Type 1 Diabetes mellitus– 1st degree relatives

» GAD / ICA512 Ab +ve … ~75% develop type 1 diabetes

– Islet cell transplantation

– Diagnosis : residual islet cell function» Prolong insulin secretion to reduce cardiac/renal disease

– Human OKT31 (Ala-Ala) within 6 weeks of diagnosis» Insulin production stable / better

» Metabolic control stable / better

» IL-10 increased, IFN- decreased Herold 2003


Oral Antigen Induces IgA

Ingestion of killed Streptococcus mutans

IgA antibody producing cells– Peripheral blood by day 7, peak day 10 – 12

Secretory IgA antibodies– Saliva & Tears by 2 weeks, peak 3 weeks

Czerkinsky C 1987


Secretory IgA - Production

IgA in blood is monomeric, >90% IgA1

Secretory IgA – polymeric, IgA1 upper respiratory & GI tract

IgA2 in colon & rectum

– Induction by antigen in Peyer’s patches– Production by IgA plasma cells in lamina propria – J chain polymerisation of IgA– Binds polymeric Ig-receptor for trans-epithelial

transport, cleaved to release secretory IgA


Secretory IgA Transepithelial Transport

Epithelial IgA Interstitial IgA/IgG Polymeric IgR / Secretory componentCrypts / Villous epithelium

Polymeric IgReceptor Deficient Mice Johansen 1999


Polymeric IgR Deficient Mice


Secretory IgA - Function

Specificity– 2 – 5% reacts with specific Ag after immunisation– Commensal flora? Dietary antigens?

Resists proteolysisInhibits microbial adherence Neutralisation of viruses, toxins (cholera)Activates complement (alternative pathway)


Selective IgA Deficiency

1 in 500 – 700 Caucasians, most are healthy! IgA-producing cells in GI tract ~absent Normal numbers of Ig-producing cells! Increased IgM (65 – 75%) & IgG (20 – 35%)

producing cells compensate– Pentameric IgM (J chain, polyclonal IgR transport)

Recurrent infections associated with additional antibody deficiencies – Poor antibody response to vaccines!


Pathogens Targeting the Mucosal Immune System

M cellsPolio

HIV

SalmonellaS.typhiS.typhimurium


Mucosal Immunity

– sIgA at mucosal surfaces, IgM + IgG in blood Live attenuated microbes

– oral Polio (Sabin) – rotavirus (rhesus/human virus with VP-7 Ag)

Killed microbes + potent adjuvants– Vibrio cholera + cholera toxin B (CTB)– ~85% protective, and cross-protection vs

enterotoxigenic E.coli (ETEC)


Conclusion

Mucosal Immune system– Antigen - induced expansion of lymphoid tissue– Lymphocyte homing– Functional and phenotypic diversity– Regulatory T cells– Immunoglobulin IgA– Immunity thru’ Vaccination


References Chen W et al. Conversion of Peripheral CD4+CD25- Naive T Cells

to CD4+CD25+ Regulatory T Cells by TGF-beta. Induction of Transcription Factor Foxp3. J Exp Med 2003; 198 (12):1875-1886.

Groh V et al. Recognition of stress-induced MHC molecules by intestinal epithelial gammadelta T cells. Science 1998; 279 (5357):1737-1740.

Herold et al. Activation of human T cells by FcR nonbinding anti-CD3 mAb, hOKT31(Ala-Ala). J.Clin.Invest. 2003; 111 (3):409-418.

Maloy et al. CD4+CD25+ TR Cells Suppress Innate Immune Pathology Through Cytokine-dependent Mechanisms. J Exp Med 2003; 197 (1):111-119.

Ostroukhova O et al. Tolerance induced by inhaled antigen involves CD4+ T cells expressing membrane-bound TGF- and FOXP3. J.Clin.Invest. 2004; 114 (1):28-38.

Immunology, Papworth Hospital, CambridgeAR Exley Mucosal Immune System Dr Andrew Exley Immunology Lab & Lung Defence Unit Papworth Hospital.

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Immunology, Papworth Hospital, CambridgeAR Exley Mucosal Immune System Dr Andrew Exley Immunology Lab & Lung Defence Unit Papworth Hospital.