Immunology Flashcards
State four aspects of the innate immune system of the eye
- blink reflex
- chemical properties
- immune cells
How does the mucous layer help protect the body?
It is anti-adhesive
What chemicals do tears contain that help fight pathogens?
Lysozyme, lipids, antimicrobials and immune mediators
Name three immune cells found in the eye
Neutrophils, macrophage and mast cells
What are the three key differences between innate and adaptive immune response?
Innate - rapid, targets group of pathogens, no memory
Adaptive - gradual, targets specific pathogens, memory
What does the adaptive immune system require?
Antigen Presenting Cells
Lymphatic Drainage
Effector Cells
What are the main antigen presenting cell for the external eye?
Langerhans Cells
Where are langerhans cells found and what are they rich in?
Highly abundant at the corneoscleral limbus rich in MCH class II molecules
Name the only part of the eye with lymphatic drainage
Conjunctiva
In the conjunctiva what are the main APC and what are these closely related to?
Dendritic cells close association with MALT
What is MALT?
Mucosa associated lymphoid tissue - clusters of cells that identify abnormal cells
Name three types of cells that make up MALT
- Macrophage
- Mast cells
- Langerhans cells
Also some commensal bacteria
Do the cornea/sclera have any lymphatic tissue?
no
Describe the immunology of the lacrimal gland
More IgA and CD8 T cells compared to conjunctiva in addition to small groups of T cells around the intralobar ducts
What mechanism prevents movement of cells in/out of the eye?
Blood ocular barrier
What is immune privilege?
Certain sites in the body are able to tolerate the introduction of antigens without electing an inflammatory immune response
Which parts of the body show immune privilege?
Testes
Placenta/foetus
Eyes
Specifically which part of the eyes have immune privilege?
Cornea, anterior chamber, lens, vitreous cavity, subretinal space
Name three mechanisms that allow the eye to have immune privilege
- blood tissue barrier and lack of lymphatic drainage
- microenvironment of immunosuppressive molecules
- anterior chamber associated immune deviation
What is the anterior chamber associated immune deviation?
Peripheral tolerance to ocular antigens - placement of a foreign antigen into the ocular microenvironment can induce a systemic form of tolerance
What is the purpose of ACAID?
Acts to protect the eye from the collateral damage of an immune response to infection
How does does ACAID protect the eye from collateral damage?
Primes T and B cells to produce non-complement fixing antibodies
Inhibits delayed type hypersensitivity
Describe the immunological ignorance of corneal cells
Reduced expression of MHC class I molecules and no expression of MHC class II or blood/lymphatic vessels
Name a rare autoimmune reaction to ocular antigens
Sympathetic Ophthalmia
Describe sympathetic ophthalmia
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’
What are the injured and other eye known as in sympathetic ophthalmia?
Injured - exciting
Fellow - sympathising
Name six autoimmune conditions of the eye
- autoimmune uveoretinitis
- dalen-fuchs nodule
- keratoconjunctivitis
- lens induced uveitis
- retina autoantibodies
- sympathetic ophthalmia
What are the key risks of a defective immune system?
Recurrent infections/cancer
What are the key risks of a hyperactive immune system?
Responds to harmless substances and self, rejects transplants and may cause allergies
Describe and give an example of a type 1 hypersensitivity reaction
IgE, mast cells and vasoactive mediators
E.g. acute allergic conjunctivitis
What is the word used to describe conjunctival oedema?
Chemosis
Describe and give an example of a type 2 hypersensitivity reaction
Direct cell killing with macrophage and complement
E.g. Ocular creatricial pemphigoid
How is ocular pemphigoid treated?
Steroids
What are the two ocular side effects of steroids?
Cataracts and glaucoma
Describe and give an example of a type 3 hypersensitivity reaction
Immune complex mediated involves accumulation of antigens bound to antibodies that fix complement
E.g. Autoimmune corneal melting
Describe autoimmune corneal melting
Outer layer of cornea melts while the inner layer bulges forward which can cause perforation
Describe and give an example of a type 4 hypersensitivity reaction
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
What must be prevented in order for a cornea transplant not to be rejected?
Vascularisation
How does immune privilege play a role in transplant acceptance?
- reduces MCH expression
- avascular cornea
- cornea deficient of langerhans
- immunosuppressive molecules
- ACAID
