Immunology of the Eye Flashcards
what is the innate immune system
first line defence - rapid response (mins-hours)
physical barrier
targets groups of pathogens
no memory
targets a limited number of bacterial structures
what is the adaptive immune system
acquired, learned, specific immunity
takes days
has memory -allows you to build tolerance to pathogen if you encounter it again
what are the innate immune features of the eye
chemical agents and immune cells
no skin barrier and few commensals
how does the eye protect itself (first line)
blink reflex - tears
Lysozyme on the eye surface (plus lots of other anti-bacterial properties)
Limit exposure/size
what layers does the tear film have
lipid layer
aqueous layer
mucin layer - anti-adhesive
what anti-microbial properties do the tears have
lysozyme (destroys cell walls) lactoferrin and transferrin antibacterial lipids angiogenin IgA complement IL6, IL8, MIP
what immune cells are in the tears
neutrophils
macrophages
conjunctival cells
what does the adaptive immune system require to work
- Antigen presenting cells
- lymphatic drainage to lymph nodes
- variety of effector cells (CD4+, CD8+ T cells, B cells)
what are the principle APCs for the external eye
Langerhans cells (rich in class II MHC molecules)
where are most langerhans cells found
at the cornea-scleral limbus - less in the peripheral cornea and ABSENT in the central 1/3 of the cornea
what part of the eye is the only part with lymphatic drainage
conjunctiva
what immune features are found in conjunctival zones
dendritic cells mucosa associated lymphoid tissue macrophages langerhans cells mast cells commensal bacteria
are the cornea and sclera avascular/vascular
avascular
what section of the cornea contains langerhans cells
peripheral cornea
the sclera and cornea have a normal immune environment true/false
false
a down regulated immune environment
what immune features are seen in the lacrimal gland
plasma cells (IgA) CD8+ T cells
what protects the vitreous compartment, choroid and retina from infection
blood-ocular barrier
Lack of APCs
Down regulated immune environment (to prevent collateral damage from immune responses)
why is the immune environment in the eye down regulated
because there is potential for a lot of collateral damage from inflammation
What is immune privilege
an active process where parts of the body are able to tolerate the introduction of antigens without eliciting an inflammatory immune response
what sites in the eye are immune-privileged
cornea anterior chamber lens vitreous cavity sub retinal space
how is ocular immune privilege established
separation: cornea is separated from immune system by lack of blood and lymphatic vessels
inhibition: development of an intraocular immunosuppressive environment
regulation: peripheral tolerance to ocular antigens (ACAID)
what is anterior chamber associated immune deviation (ACAID)
if a pathogen gets into the anterior chamber, peripheral tolerance to the antigen occurs
- suppressed a future potentially damaging response to infection
what is sympathetic ophthalmia
rare bilateral granulomatous uveitis due to trauma or surgery to 1 eye
(secondary development of autoimmune reaction to ocular antigens exposed during trauma)
Disadvantage of immune privilege - related to the immune isolation of the eye
what are the primary mediators in sympathetic ophthalmia
T cells
what is the injured eye called in sympathetic ophthalmia
exciting eye
other eye is the sympathising eye- can only tell the difference from history
what are some side effects of a defective/absent immune system
recurrent (severe) infections ignores innocuous substances tolerance to self acceptance of transplanted organs/tissues cancer
what are the side effects of a hyperactive immune system
protection from harmful pathogens
responds to innocuous substances
responds to self
rejection of transplanted organs/tissues
what is a type 1 hypersensitivity reaction
ALLERGIC RESPONSE
B cells encounter allergens so produces IgE - clears allergen
mast cells bind to the left over IgE which wasn’t cleared
this means next time the pathogen is encountered, because the IgE is already attach to the mast cells it immediately reacts to the pathogen
mast cells release loads of inflammatory mediators
what is an example of a type 1 hypersensitivity reaction in the eye
acute allergic conjunctivitis
what is a type 2 hypersensitivity reaction
direct killing/antibody response
The pathogen is killed by either Macrophages/NK cells or complement
what is an example of a type 2 hypersensitivity reaction in the eye
ocular cicatrical pemphigoid
type of autoimmune conjunctivitis: blistering and scarring of the conjunctiva
what is type 3 hypersensitivity
Immune complex mediated
Immune system produces too much antibody and the complexes can’t get cleared leading to inflammation
example of type 3 hypersensitivity in the eye
Autoimmune corneal melting
what is type 4 hypersensitivity
delayed type
complex reactions which take a long time to come about but are v adapted
clonal expansion of T cells lead to an exaggerated immune response
example of type 4 hypersensitivity reactions in the eye
corneal graft rejection
what factors in the eye help maintain immune privilege
reduced and impaired expression of MHC I and II molecules in cornea
cornea lacks blood and lymph vessels
Central cornea is deficient in lagerhands
secretion of molecules with immunosuppressive properties inhibits immune cells
expression of surface molecules to inhibit immune effectors
ACAID in the peripheral immune system
side effects of steroids in the eye
cataracts
steroid-induced glaucoma
