Immunology Flashcards
innate immunological barriers that are not present in the eye
- no physical barrier as no skin
- not many commensal bacteria
solutions to the lack of physical barrier in the eye
blink reflex
physical and chemical agents
limiting exposure e.g. eye sits back in the head
physical barrier of tears
tears are flushed across the eye when blinking
cornea contains a mucous layer that is anti-adhesive preventing microorganisms and dirt from sticking to the eye
chemical barrier of tears
lysozymes lactoferrin lipids angiogenin sIgA complement IL-6 IL-8 MIP
cellular barrier of tears
neutrophils
macrophages
conjunctival mast cells
adaptive immune system in the eye
langerhans cells (APC)
where are Langerhans cells abundant?
corneo-scleral limbus with less in peripheral cornea and absent from central 1/3rd
immunological properties of conjunctiva
- only part with lymphatic drainage
- endothelial venules (regulate migration of immune cells)
- diffuse effector cells in conjunctival zones (T and B cells)
- MALT (mucosa associated lymphoid tissue) contains macrophages, Langerhans and mast cells
- commensal bacteria
is the cornea and sclera a downregulated immunological layer of the eye?
yes
cornea and sclera immunological properties
- tough collagen is avascular with no lymphatics
- langerhans in peripheral cornea and corneo-scleral limbus
describe the lacrimal gland and drainage system immunological properties
- lacrimal gland has plasma cells e.g. IgA and CD8+ T cells (intralobar ducts)
- drainage contains diffuse lymphoid tissue and follicles in mucosa MALT
is the vitreous, choroid and retina a downregulated immunological part of the eye?
yes
describe immunological properties of vitreous, choroid and retina?
blood-ocular barrier
lack of APCs
what is immune privilege?
able to tolerate antigens without eliciting an inflammatory immune response
how is the eye able to have immune privilege?
- blood-tissue barrier
- lack of lymphatic drainage
- rich in immunosuppressive cells and inhibitory surface molecules
- ACAID
what does ACAID stand for?
anterior chamber-associated immune deviation
what is ACAID
placement of foreign antigen into the ocular environment induces a systemic tolerance to the foreign antigen
why does the eye have immune privilege?
protects it from collateral damage from an immune response
three ways the establishment of ocular immune privilege occurs
- separation: reduced MHC, cornea lacks blood and lymphatic vessels
- inhibition: inhibitory components
- regulation: ACAID
define sympathetic opthalmia
bilateral granulomatous uveitis
cause of sympathetic opthalmia
development of an AI reaction due to ocular antigens expose during the causative event
causative event of sympathetic opthalmia
trauma
surgery
example of a disadvantage of immune privilege
sympathetic ophthalmia
in sympathetic ophthalmia what is the injured eye called?
exciting eye
in sympathetic ophthalmia what is the uninjured eye called?
sympathising eye
describe how sympathetic ophthalmia occurs?
- trauma in one eye results in release of intraocular antigens
- carried to lymph nodes and activate T cells
- T cells return in bloodstream and encounter antigen in both eyes (lack of specificity)
examples of ocular AI diseases
- Autoimmune uveoretinitis= inflammation of the uvea and retina
- Dalen-Fuchs nodule= epithelial cell clusters in retinal layers
- Keratoconjunctivitis sicca (dry eyes)
- Lens-induced uveitis= reaction to release of lens products
- Retina autoantibodies= common in retinopathy associated with cancer/infection/ degenerative disease
- Sympathetic ophthalmia= bilateral granulomatous uveitis.
define hypersensitivity reaction
immune response that results in bystander damage to self
what is the classification system used for hypersensitivity?
Gel and Coomb’s
describe type 1 (immediate hypersensitivity)
- encountering an antigen B cells produce IgE which targets the pathogen and its cleared
- excess IgE is produced and so binds to Fc receptors on mast cells
- upon re-encounter B cells are not needed as there is excess IgE
- mast cells release IgE and there own vasoactive substances e.g. histamine
describe type 2 (direct cell killing/ antibody-mediated cytotoxicity)
cells are killed by NK cells (macrophages) or complement (MAC)
examples of direct cell killing (type 2) condition
ocular cicatricial pemphigoid
presentation of ocular cicatricial pemphigoid
blisters on eyelids and eye surface
healing leads to scarring and adhesions
lid can be held open
management of ocular cicatricial pemphigoid
steroids
describe type 3 (immune complex mediated)
antigen-antibody complexes are formed and deposited in various tissues
example of type 3 condition
AI corneal melting (inner layer bulges forward so can risk perforation)
management of type 3 (AI corneal melting)
steroids
describe type 4 (delayed/ cell-mediated cytotoxicity)
T cells are activated by intracellular pathogens and undergo clonal expansion
re-exposure produces an exaggerated immune response
example of type 4 condition
corneal graft rejection (rare due to immune privilege)
there is vascularisation of host cornea reaching donor tissue
factors that maintain immune privilege
- reduced MHC I and II
- cornea lacks blood and lymph vessels
- central cornea lacks Langerhans (lengthens time for graft recognition)
- secretion of immunosuppressive cells and expansion of surface molecules inhibiting immune effectors (ACAID in recipients)
ocular side effects of steroids
cataracts
steroid-induced glaucoma
