Ocular Immunology/ Uveitis

Kyle C. McKenna, Ph. D.Associate Professor of Biology and Ophthalmology

mckennakc@upmc.edu

HypopyonOcular infiltrate of white blood cells(leukocytes) which settle via gravityto the bottom of the anterior chamber“like sands through the hour glass”

How did the leukocytes get there?

Leukocytes (cells of the immune system travelVia blood and enter the eye via vessels in theiris, ciliary body, choroid, retina, and sclera

Blood Smear

Basophil

MonocyteBand Cell

Eosinophil

Lymphocyte

Lymphocyte

Neutrophil

Neutrophil

1

2

34 5

65

1

Granulocytes

Neutrophil Eosinophil Basophil

Mast Cells

Monocytes

Macrophages

Lymphocytes

B CellsT Cells

T T

CD4+Thelper

CD8+CTL

Innate Immunity Adaptive Immunity

Complement

Antibody

• Immediate• Includes anatomical

and biochemical barriers

• Recognition of conserved pathogen associated molecular patterns (PAMPs)

• No memory generation

• Delayed• Specific recognition of

pathogenic molecules• Memory Generation

Innate Adaptive

PAMP PRRPathogen Recognition Receptor

Lipopolysaccharide (LPS) TLR 4Toll Like Receptor

Double Stranded RNA TLR 3

DAMPDamage associated molecular pattern

DRRDamage Recognition Receptor

HMGB1(High MobilityGroup box 1)

RAGE, TLR 2, 4 and 9Receptor of advanced glycation endproduct

Nonoxidized (reduced) HMGB1 is released by normal cells upon necrotic butNot apoptotic cell death

PAMPs and DAMPs promote inflammation

IL-1IL-6

TNFNitric oxide

IL-8

Increased Cell Surface moleculesMHC Class I & IICD40, CD80, CD86

Produce inflammatory cytokinesIL-12TNF

Activated Antigen PresentingCells Leave via afferent lymphatics

MacsDC

RednessSWELLINGPAIN

Spleen

Secondary Lymphoid Organs

Innate immunity is immediate but alone insufficient for pathogen control

Adaptive ImmunityB-Cells T-Cells

Antigen Receptor: Immunoglobulin TCRRecognition: Proteins, Carbohydrates

Lipids, most any moleculeProcessed Proteins Presented as

Peptides via MHC molecules by APC

ExogenousProteins via

MHC Class II

EndogenousProteins via

MHC Class I

ProfessionalAPC

All Cells inBody

From Eye

APC

FreeAntigen

B

B

B

BB

B

B

B

B

T

T

T

T

T

T

T

T

T

T

TT

T

T

FDC

More ProliferationHere

Clonal Expansion

Diverse RepertoireOf B cells and T cell

Increase NumbersOf Antigen Specific

Clones

Differentiation

Memory Cells

Antibody SecretingPlasma Cells

T helper Subsets

CTL

Process of Expansion and Differentiation takes time which is why AdaptiveImmunity is Delayed

Eff

ecto

rs

APC

CD4+T helper

IL-2

IL-2IFN

CD8+CTL

Lytic granulesContaining Granzyme B Lysis of infected Cells

IFN

B cells

IgG2aViral and Bacterial infections

IL-4, 5, 6, 10

B cells

IgG, IgEExtracellular Helminthic Infections

What determines uniqueThelper differentiation?

PAMPS / APC

APCIL-12

LPS/TLR4

TH1

APCIL-4

Filaria?

TH2

Infections Activate InnateImmunity via PAMPS

T and B cell expansionAnd differentiation occur

Blood Stream

Activated APCLeave eye CarryingPathogenic Molecules

AfferentLymphatics

LymphNode

EfferentLymphatics

What is Type I Hypersensitivity?

Immediate Hypersensitivity

Antibody Mediated (IgE)

IgE molecules are bound by FcEpsilon receptors on Mast Cells

Mast Cells release histamines which promote inflammation

Allergic Conjunctivitis

What is Type II Hypersensitivity?

Antibody Mediated

Cell lysis via Antibody Dependent Cellular Cytotoxicity

Rh Hemolytic anemia in newborns

Sympathetic ophthalmia, Uveitis

CompMAC

Phagocytosis

What is Type III Hypersensitivity?

Antibody Complex Mediated

Antibody Complexes Fix Complement Leading to productionOf anaphylotoxins which promote inflammation

CompMAC

CompMAC

CompMAC C3a, C5a

AnaphlotoxinsPromote vasodilationAnd leukocyteinfiltration

What is Type IV Hypersensitivity?

Delayed Type Hypersensitivity

T cell mediated (CD4 TH1 cells)

CD4+ T cells activate macrophages to release inflammatory mediators(TNFa, Nitric Oxide) which causes nonspecific damage of innocent bystanderTissues

Promote infiltration of neutrophils which further enhance inflammation

CD4+T helper MAC

IFN

Nitric OxideTNF

What is Type V Hypersensitivity?

Antibodies are generated which are stimulatory

Graves DiseaseAnti-thyroid stimulating hormone receptor antibodiesstimulate the effects of Thyroid Stimulating Hormone

TSH

TSHR

Antibody

TCR and Immunoglobulin molecules are generated by Random Somatic Rearrangement of gene segments

What is the potential complication of this process?

Generation of TCR and Immunoglobulin molecules that recognize self tissues

T cells expressing TCR with strong reactivity to self antigens are deletedIn the Thymus during T cell development

What is the consequence of overly stringent negative selection?

Decreased Repertoire of the T cell pool

Fact: T cells and B cells are generated with receptors that demonstratesome affinity for self antigens.

Why are we not in a constant state of autoimmunity?

Peripheral tolerance mechanisms

Three Signals are Required for Full T cell activation

3

Cytokines

1. TCR : MHC/peptide2. Costimulatory Molecules3. Cytokine Production

In the absence of three signalsT cell anergy or tolerance is generated

How do PAMPS break tolerance toSelf antigens?

PAMPS increase costimulatory moleculesAnd cytokine expression

UveitisClassic T cell dependent Type IV hypersensitivity response

Infectious (syphilis, tuberculosis, toxoplasma gondii)Noninfectious (self antigens)[mouse models via immunization with IRBP, Retinal S-ag]

Disease Associations made with particular MHC moleculesHLA-B27 : Reiter’s syndromeHLA-B5: Behcet’s DiseaseHLA-29: Birdshot Choroidopathy

How could an immune response to an ocular antigen develop toCause autoimmune uveitis?

Retention of T cells with specificity to ocular antigens due toWeak negative selection in individuals with particular HLA types

Previous infection or trauma primed for ocular antigens in anInflammatory context

Molecular Mimicry (Klebsiella, Chlymidia, Yersinia?)

Ocular Immune PrivilegeCharacterized by prolonged acceptance of foreign immunogenic graftsIn comparison to conventional sites

Corneal Allografts most successful (no matching, minimal immunosuppression required)

Experimentally immunogenic tumors grow progressively in the anteriorChamber but are eliminated by CD8+ T cells when transplanted in theskin

Anatomical Barriers to Host Immune Response

Cornea is avascular

Interior of Eye lacks demonstrable lymphatic drainage

Blood Aqueous Barrier

Blood Retinal Barrier

Biochemical Barriers to Host Immune Response

Aqueous Humor contains Immunosuppressive soluble factors(TGF-b, a-MSH, IL-10, MIF, CGRP, VIP, somatostatin)

Interior Cell Surface expresses Death inducing Molecules(FasL, Trail, PD-1 and PD-2L)

T cell anergy, T cell death, T regulatory generation

Tolerance Induction to Ocular Antigens

Introduction of foreign antigens into the anterior chamber, subretinal spaceAnd vitreous cavity induces systemic tolerance to these antigens

Mediated by the generation of Tregulatory cellsCD4, CD8+