Immunology

Question 1

Innate immune system of the eye

Answer 1

Blink reflex

Physical and chemical properties of eye surface

Limit exposure/ size

Question 2

Blink reflex- tears

Answer 2

Tears: physical

• flushing
• mucous layer= anti-adhesive

Tears: chemical

• lysozyme, lactoferrin, transferrin
• tear lipids
• angiogenin
• secretory ILA
• complement
• Il-6, Il-8, MIP

Tears; cellular

• neutrophils
• macrophages
• conjunctival mast cells

Question 3

Adaptive Immune system of eye

Answer 3

Antigen presenting cells (APCs)
- dendritic cells, B cells, macrophages

lymphatic drainage to. lymph node

Variety of effector cells

Question 4

Langerhan Cells

Answer 4

Principle antigen presenting cell for external eye

Rich in class II MHC molecules

Abundant at corner-scleral limbus
Less in peripheral cornea
Absent from central ⅓ of cornea

Question 5

Conjunctiva

Answer 5

Only part of the eye with lymphatic drainage

Specialised endothelial venues for regulated migration of lymphoid cells

Diffuse lymphoid populations in all conjunctival zones
- CD4+ & CD 8+ T cells, IgA secreting plasma

Dendritic cells act as APCs

Mucosa associated lymphoid tissue (MALT)
- macrophages, langerhans and mast cells

Commensal bacteria

Question 6

Cornea and Sclera

Answer 6

‘Tough collagen coat’

Avascularity

No lymphatics or lymphoid tissue
Relative lack of APCs

langerhans cells only in peripheral cornea

Downregulated environment

Question 7

Lacrimal Gland

Answer 7

More plasma cells (IgA) and CD8+ T cells compared to conjunctiva

T cells in small groups around interlobular ducts

Question 8

Lacrimal Gland drainage system

Answer 8

Diffuse lymphoid tissue and follicles in mucosa (MALT)

Question 9

Vitreous, Choroid and Retina

Answer 9

Blood-ocular barrier

Relative lack of APCs

Downregulated immune environment

Question 10

Immune privilege site

Answer 10

Able to tolerate introduction of antigens without exciting an inflammatory response

Question 11

Sites of immune privilege in eye

Answer 11

Cornea
Anterior. chamber
Lens 
Vitreous Cavity
Sub-retinal space

Question 12

Ocular immune privilege mechanisms

Answer 12

Unique anatomical features of blood-tissue barrier and lack of direct lymphatic drainage

Ocular environment is rich in immunosuppressive molecules and inhibitory cell surface molecules that influence the reactivity of immune cells

Anterior chamber associated immune deviation
- ACAID

Question 13

Anterior chamber associated immune deviation

Answer 13

Placement of foreign antigen. into ocular microenvironment can induce a systemic form of tolerance to foreign antigen

‘Peripheral tolerance’ to ocular antigen

ACAID protects the eye and visual axis from collateral damage of an immune response to infection by suppressing a future potentially damaging response to infection

Question 14

Establishment of Ocular Immune Privilege

Answer 14

Separation
Inhibition
Regulation

Question 15

Establishment of Ocular Immune Privilege: Separation

Answer 15

Immunological Ignorance

Corneal cells have decreased expression of MHC class I and do not express MHC class II

Cornea lacks blood and lymphatic vessels

Question 16

Establishment of Ocular Immune Privilege : Inhibition

Answer 16

Development of an intraocular immunosuppressive microenvironment

Question 17

Establishment of Ocular Immune Privilege : Regulation

Answer 17

Peripheral tolerance to ocular antigens

–> ACAID

Question 18

Sympathetic Ophthalmia

Answer 18

Rare, bilateral, granulomatous uveitis due to trauma or surgery to one eye

Question 19

Sympathetic Ophthalmia pathophysiology

Answer 19

Primary mediator: T cells

Initial wave of infiltrative cells composed of CD4+ helper T cells.
Later wave of infiltrative cells are CD8+ Cytotoxic T cells

Question 20

Sympathetic Ophthalmia Clinical

Answer 20

Injured eye: ‘exciting’ eye
Fellow eye: ‘sympathising’ eye

Clinically. both eyes will appear the same
History is required to determine exciting eye

Question 21

Ocular Autoimmune Diseases (5)

Answer 21

Autoimmune uveoretinities
- inflammation of urea and retina

Dalen-Fuchs Nodule
- Epithelial cells clusters in retinal layers

Jerato conjunctivitis Sicca
-dry eyes

lens-induced uveitis
- reaction due to release of lens products

Retina autoantibodies
- common in retinopathy associated with cancer/ infection/ degenerative disease

Question 22

Hypersensitivity Reactions

Answer 22

Type I: Immediate Hypersensitivity
Type 2: Direct cell killing
Type 3: Immune complex mediated
Type 4: Delayed type hypersensitivity

Question 23

Type 1 : Immediate hypersensitivity

Answer 23

Acute allergic conjunctivitis

- chemosis: oedema of conjunctivitis

Question 24

Type 2: Direct Cell Killing

Answer 24

(Antibody mediated cytotoxicity)

Ocular Cicatricial Pemphigoid

• Type of autoimmune conjunctivitis
• BListering and scarring of conjunctiva

Question 25

Type 3: Immune complex mediated

Answer 25

Outer layer of cornea melts and inner layer bulges forward: possible perforation

Question 26

Type 4: Delayed hypersensitivity

Answer 26

Corneal Graft rejection

- vascularisation of host cornea reaching the donor tissue = graft rejection

Question 27

Corneal Transplants and Immune Privilege

Answer 27

Factors that maintain immune privilege:

Reduced and impaired expression of MHC
Class I and Class II molecules in corneal cells
-reduced net antigenic load

Cornea lacks blood and lymph vessels

Central cornea is deficit in Langerhans Cells

Secretion of molecules with immunosuppressive properties

Expression of surface molecules that inhabit immune effectors

ACAID in recipients