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UNIVERSITÄT BERN OCULAR IMMUNOLOGY Christine Watté, DVM, Dipl.ECVO BSC 22 June 2016; NCSU Plan of the lecture 1. GENERAL PRINCIPLES OF IMMUNOLOGY 2. DEFENSE MECHANISMS OF TEARS AND OCULAR SURFACE 3. IMMUNE PRIVILEGE OF THE CORNEA 4. OCULAR IMMUNE PRIVILEGE, ACAID, THERAPEUTIC APPLICATIONS 5. IMMUNE MECHANISMS OF SELECTED DISEASES Why study ocular immunology? PART 1: GENERAL PRINCIPLES OF IMMUNOLOGY When is the immune system active? When is the immune system active? What is Immunology? • Not just the host response against infectious agents • Study of all mechanisms leading to recognition and response against what is recognized as foreign (non-self) • Purposes: • Fighting pathogens (bacteria, viruses, fungi, parasites) • Tolerance against commensals • Regulating auto-reactivity The immune system sees things differently See /hear Molecules / Receptors Knowledge Knowledge Learning Learning Innate and adaptive immunity 1st Line defense 2nd Line defense Specificity of innate and adaptive immunity Innate Adaptive Specificity of innate and adaptive immunity Innate Adaptive Specificity of innate and adaptive immunity Innate Adaptive Specificity of innate and adaptive immunity Innate Adaptive Specificity of innate and adaptive immunity Innate Adaptive Innate Immunity Pattern Recognition Receptors Examples: • Toll-like Receptors (TLRs) • Nod-like receptors (NLRs) • RIG-I-like Receptors (RLRs) • Mannose-Binding Lectin (MBL) Present in all cellular compartments Can differentiate between broad classes of pathogens PRRs signal the earliest events in inflammation INFKb: Nuclear factor-Kb; IRFs: Interferon regulatory factor PRR recognize microbes & danger Molecular structures that are characteristic of microbes Pathogen-Associated Molecular Patterns (PAMPS) Host molecules released from damaged or dying cells Damage-Associated Molecular Patterns (DAMPS) Innate Immunity Complement Proteins Adaptive Immunity Abbas, Lichtman, and Pillai. Cellular and Molecular Immunology, 7th edition. Copyright © 2012 by Saunders, an imprint of Elsevier Inc. CD4 Th cells can differentiate in subsets with distinct functions Phases of adaptive immune responses Specificity Memory and Contraction Regional Immunity Cance Viruses r Fungi IMMUNE Bacteria SYSTEM Parasites Toxins Pollution Specialized Immune Responses in Epithelial and Immune Privileged Tissues Diverse ocular tissues with different challenges • Microbes at the ocular surface • Preserve optical clarity • Little regenerative capacity Immune responses in the eye are adapted to suit the functional needs of the diverse ocular tissues 1st Line Protection Vision Plan of the lecture 1. GENERAL PRINCIPLES OF IMMUNOLOGY 2. DEFENSE MECHANISMS OF TEARS AND OCULAR SURFACE 3. IMMUNE PRIVILEGE OF THE CORNEA 4. OCULAR IMMUNE PRIVILEGE, ACAID, THERAPEUTIC APPLICATIONS 5. IMMUNE MECHANISMS OF UVEITIS LET’S TAKE A BREAK PART 2: DEFENSE MECHANISMS OF TEARS AND OCULAR SURFACE Healthy ocular surface Lubrication Resist Commensal pathogenic flora microbes Multiple layers of protection • Anatomic and physical barriers • Defense mechanisms of tears • Defense mechanisms of ocular epithelia • Eye associated lymphoid tissue Eyelids & Eyelashes Eyelids • Protect the eyeball • Wipe the eye clean • Distribute the tear film • Shunt tears to the lacimal puncta • Secrete the lipid layer Eyelashes • Prevent fine particles from entering the eye McCurnin; Small Animal Physical Diagnosis and Clinical Procedures (1991) Tears wash and eyelids wipe Tears: more than lubrication Aqueous tears Mucins Antimicrobial proteins and peptides Complement Immunoglobulins Mucins: High molecular weight glycoproteins Dryeyes.com mucin_sigmaaldrich.com. Mucin producing tissues of the eye Lacrimal gland Cornea MUC1 MUC4 MUC16 MUC5AC Conjunctiva & Goblet cells Gipson IK, Exp Eye Res 2004 Type and origin of mucins Source Mucin gene Mucin type Epithelial cells MUC1 MUC4 MUC16 Membrane Associated Goblet cells MUC5AC MUC5B MUC 2 Gel Forming Lacrimal gland MUC1 MUC4 MUC5B MUC7 Small Soluble Paulsen; Int Rev Cyto (2006) Mucins hold water Hydrate the epithelium & stabilize the tear film Mucins: front line defenders of the ocular surface • Repulse or trap microorganisms • Reservoir of antimicrobial proteins and peptides • Binding sites for surveiling neutrophils • Maintain a healthy CALT • Wound healing • During infection: • Increased mucus secretion • Altered glycosilation • Cleavage of transmembrane mucins of the glycocalix • Intracellular signaling to increase cellular resistance to infection CALT: Conjunctiva Associated Lymphoid Tissue Antimicrobial proteins and peptides (AMP): A chemical barrier against microbes Source: • Lacrimal glands and epithelium • Serum exudates • Infiltrating cells Target: • Bacteria, fungi and viruses MS Gregory, Innate immune system and the eye, 2011 AMP: the shortlist Lactoferrin Complement Lipocalin α and β Defensins Lysozyme Cathelicidin Secretory phospholipase A2 Surfactant proteins Secretory IgA …………….. Dog tear film protein analysis 125 different proteins in the tear film of healthy dogs Dog Tear Film Proteome In-Depth Analysis. Winiarczyk M et al. (2015) PLoS ONE Lactoferrin Complement Lipocalin α and β Defensins Lysozyme Cathelicidin Secretory phospholipase A2 Surfactant proteins Redundancy If the immune system falls short of one factor, most of the time it can compensate forSecretory this deficit IgA with other factors ……….. Dynamic regulation of AMP Lysozyme, lactoferrin, lipocalin, Open eyes sIgA Increased sIgA, complement, Closed eyes serum derived proteins and PMN Ocular infection More potent defensins Effect of AMP on Microorganisms Action Substance Lysozyme, secretory phospholipase A2, cathelicidin, Disrupt microbial membrane defensin, SLP1, Complement factors Interfere with microbial growth Lactoferrin, Lipocalin A, SP-D Interfere with microbial adherence Lactoferrin Neutralize and/or aggregate toxins sIgA, Defensin and microorganisms SLP1: secreted leukocyte protease inhibitor-1 Effect of AMP on the Epithelium Action Substance Promote proliferation defensins, cathelicidins Inhibit bacterial adhesion and invasion SP-D, lactoferrin Amplify apoptosis of infected cells lactoferrin SP-D: surfactant protein D Effect of AMP on Immune Cells Action Substance Chemoattract Immune cells SP A-D Opsonization IgA, complement Promote pahgocytosis Defensins, complement Potentiate bactericidal activity of Neutrophils Lactoferrin Reduce inflammation (through neutralization of Cathelicidin, defensins bacterial toxins) SP A-D: surfactant protein A&D Lysozyme • Function: • Enzyme: disrupts bacterial cell wall • Quantity: • Major tear protein in people Tear lysozyme concentration in people estimated by the agar diffusion • Low quantity in dogs tears technique (substrate: Micrococcus lysodeikticus) • present in sheep, goats, llamas, cattle, horses, dogs, and rabbits Positively charged peptides (e.g. Defensins & Cathelicidin) Positively charged AMP Negatively charged microbial membrane Pore formation Cell lysis Complement • Constitutive low-level expression of activated complement proteins in tears (e.g. C3, C4, factor B) • Source: • Ocular epithelia • Serum • PMN • Enable rapid and controlled activation of the complement cascade Complement proteins Factor B C4 Immunoglobulins • Secretory IgA, IgG, IgM • Variable concentrations within healthy canine tears • Age • Time of day • Day to day variations Secretory IgA • Dimeric antibody • Junction chain • Secretory component • Plasma cells in the conjunctiva and lacrimal glands • Transported through the epithelium Koeppe & Stanton: Berne and Levy physiology 6thed; 2008 Secretory IgA: How does it work? • Form Immune Complexes (IC) Agglutinate and neutralize microbes Antigen-specificity non-specific Ag binding (glycans) SEM IgA-mediated agglutination of Salmonella typhimurium Mantis N.J. Mucosal Immunology 2011 Secretory IgA • Immune complexes reinforce epithelial barrier function • Favors commensals close to Epithelium the epithelium • Inhibit microbial invasion of the epithelium • IC uptake by M cells Mantis N.J. Mucosal Immunology 2011 Tear IgG • Low concentrations • Produced during re-exposure • Diffuses passively or actively transcytosed • Mode of action: • Activate the complement cascade • Promote phagocytosis by macrophages Kill Microbes Tear IgM • Low concentrations (pentamer, large molecular weight) • Produced during primary infection • Mode of action: • Activate the complement cascade Kill Microbes M. R. Ehrenstein & C. A. Notley; Nature Reviews Immunology 2010 Epithelial defense mechanisms • Tight junctions • High cell turn-over • Pattern Recognition Receptors (e.g. TLRs) Abelson, Rev Ophthalmol; 2009 PRR: Toll-Like Receptors • Total of 10 TLR in humans • All 10 TLRs are present in the eye • Ocular surface • Iris, ciliary body, choroid and RPE • Key receptors that signal the earliest events in inflammation • Release of inflammatory mediators • Chemotaxis of immune cells • Expression of adhesion molecules Regulation of TLR-signaling • Spatial regulation of TLR expression • Basal and wing cells (e.g.TLR5 for flagellin) • Intracellular compartments (e.g. TLR2&4 for lipopeptide and LPS) • Modulation of inflammatory signals after TLR5 stimulation by flagellin from pathogenic bacteria versus commensal bacteria LPS: Lipopolysacharade TLRs on the equine ocular surface TLR mRNA expression in the corneal, limbal and conjunctival epithelium K. Gornik et al, Vet Ophthalmol 2011 Eye associated lymphoid tissue • Functionally linked to the mucosal immune system • Eye Associated Lymphoid Tissue • Lacrimal
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