Immunology

Question 1

State four aspects of the innate immune system of the eye

Answer 1

• blink reflex
• chemical properties
• immune cells

Question 2

How does the mucous layer help protect the body?

Answer 2

It is anti-adhesive

Question 3

What chemicals do tears contain that help fight pathogens?

Answer 3

Lysozyme, lipids, antimicrobials and immune mediators

Question 4

Name three immune cells found in the eye

Answer 4

Neutrophils, macrophage and mast cells

Question 5

What are the three key differences between innate and adaptive immune response?

Answer 5

Innate - rapid, targets group of pathogens, no memory

Adaptive - gradual, targets specific pathogens, memory

Question 6

What does the adaptive immune system require?

Answer 6

Antigen Presenting Cells
Lymphatic Drainage
Effector Cells

Question 7

What are the main antigen presenting cell for the external eye?

Answer 7

Langerhans Cells

Question 8

Where are langerhans cells found and what are they rich in?

Answer 8

Highly abundant at the corneoscleral limbus rich in MCH class II molecules

Question 9

Name the only part of the eye with lymphatic drainage

Answer 9

Conjunctiva

Question 10

In the conjunctiva what are the main APC and what are these closely related to?

Answer 10

Dendritic cells close association with MALT

Question 11

What is MALT?

Answer 11

Mucosa associated lymphoid tissue - clusters of cells that identify abnormal cells

Question 12

Name three types of cells that make up MALT

Answer 12

• Macrophage
• Mast cells
• Langerhans cells
  Also some commensal bacteria

Question 13

Do the cornea/sclera have any lymphatic tissue?

Answer 13

no

Question 14

Describe the immunology of the lacrimal gland

Answer 14

More IgA and CD8 T cells compared to conjunctiva in addition to small groups of T cells around the intralobar ducts

Question 15

What mechanism prevents movement of cells in/out of the eye?

Answer 15

Blood ocular barrier

Question 16

What is immune privilege?

Answer 16

Certain sites in the body are able to tolerate the introduction of antigens without electing an inflammatory immune response

Question 17

Which parts of the body show immune privilege?

Answer 17

Testes
Placenta/foetus
Eyes

Question 18

Specifically which part of the eyes have immune privilege?

Answer 18

Cornea, anterior chamber, lens, vitreous cavity, subretinal space

Question 19

Name three mechanisms that allow the eye to have immune privilege

Answer 19

• blood tissue barrier and lack of lymphatic drainage
• microenvironment of immunosuppressive molecules
• anterior chamber associated immune deviation

Question 20

What is the anterior chamber associated immune deviation?

Answer 20

Peripheral tolerance to ocular antigens - placement of a foreign antigen into the ocular microenvironment can induce a systemic form of tolerance

Question 21

What is the purpose of ACAID?

Answer 21

Acts to protect the eye from the collateral damage of an immune response to infection

Question 22

How does does ACAID protect the eye from collateral damage?

Answer 22

Primes T and B cells to produce non-complement fixing antibodies
Inhibits delayed type hypersensitivity

Question 23

Describe the immunological ignorance of corneal cells

Answer 23

Reduced expression of MHC class I molecules and no expression of MHC class II or blood/lymphatic vessels

Question 24

Name a rare autoimmune reaction to ocular antigens

Answer 24

Sympathetic Ophthalmia

Question 25

Describe sympathetic ophthalmia

Answer 25

Uveitis due to trauma or surgery resulting in bilateral granulomatous due to an initial wave of CD4 T cells followed by a later wave of CD8 T cells. Immune cells are sent to both eyes post penetration to attack the ‘antigen’

Question 26

What are the injured and other eye known as in sympathetic ophthalmia?

Answer 26

Injured - exciting

Fellow - sympathising

Question 27

Name six autoimmune conditions of the eye

Answer 27

• autoimmune uveoretinitis
• dalen-fuchs nodule
• keratoconjunctivitis
• lens induced uveitis
• retina autoantibodies
• sympathetic ophthalmia

Question 28

What are the key risks of a defective immune system?

Answer 28

Recurrent infections/cancer

Question 29

What are the key risks of a hyperactive immune system?

Answer 29

Responds to harmless substances and self, rejects transplants and may cause allergies

Question 30

Describe and give an example of a type 1 hypersensitivity reaction

Answer 30

IgE, mast cells and vasoactive mediators

E.g. acute allergic conjunctivitis

Question 31

What is the word used to describe conjunctival oedema?

Answer 31

Chemosis

Question 32

Describe and give an example of a type 2 hypersensitivity reaction

Answer 32

Direct cell killing with macrophage and complement

E.g. Ocular creatricial pemphigoid

Question 33

How is ocular pemphigoid treated?

Answer 33

Steroids

Question 34

What are the two ocular side effects of steroids?

Answer 34

Cataracts and glaucoma

Question 35

Describe and give an example of a type 3 hypersensitivity reaction

Answer 35

Immune complex mediated involves accumulation of antigens bound to antibodies that fix complement
E.g. Autoimmune corneal melting

Question 36

Describe autoimmune corneal melting

Answer 36

Outer layer of cornea melts while the inner layer bulges forward which can cause perforation

Question 37

Describe and give an example of a type 4 hypersensitivity reaction

Answer 37

Delayed type, T helper cells are activated by intracellular pathogens leading to clonal expansion and on re-exposure macrophage attack leading to an exaggerated response
E.g. transplant rejection

Question 38

What must be prevented in order for a cornea transplant not to be rejected?

Answer 38

Vascularisation

Question 39

How does immune privilege play a role in transplant acceptance?

Answer 39

• reduces MCH expression
• avascular cornea
• cornea deficient of langerhans
• immunosuppressive molecules
• ACAID