Physiology: Immunology and the Eye Flashcards
What is the immunological function of the blink reflex?
Tears flush the surface of the eye
What is the immunological function of the mucous layer of the eye?
Acts as an anti-adhesive
Name two antimicrobial agents found within tears
Lysozyme, secretory IgA
Name the immune cells found in tears
Neutrophils, macrophages and conjunctival mast cells
Name the principle antigen presenting cell (macrophage) for external eye
Langerhans cells
Where is the concentration of Langerhans cells highest?
Corneo-scleral limbus
Langerhans cells are rich in class ___ MHC molecules
II
Name the only part of the eye with lymphatic drainage
Conjunctiva
Name immune cells always present in the MALT of the conjunctiva
Macrophages, Langerhans cells and mast cells
Name the immune cells found in the cornea and sclera
No lymphatics/lymphoid tissue, relative lack of APCs, Langerhans cells only in peripheral cornea
Name the immune cells found in the lacrimal gland
More plasma cells (IgA) and CD8+ T cells compared to conjunctiva
T cells in small groups around intralobar duct
Resting lymphoid cells rarely observed
Where is MALT found in the eye?
Conjunctiva, lacrimal drainage
What is the blood-ocular barrier?
Barrier created by endothelium of capillaries of the retina and iris, ciliary epithelium and retinal pigment epithelium
What is immune privilege?
Certain sites of the human body, including in the eyes, have immune privilege; they are able to tolerate the introduction of antigens without eliciting an inflammatory response
Name the areas in the eye which have immune privilege
Cornea, anterior chamber, lens, vitreous cavity, subretinal space
Name three mechanisms by which the eye achieves immune privilege
- Anatomical, cellular, and molecular barriers in the eye (blood-ocular barrier, lack of lymphatic drainage)
- Eye-derived immunological tolerance - anterior chamber-associated immune deviation (ACAID)
- Immune suppressive intraocular microenvironment
What is sympathetic ophthalmia?
Rare, bilateral granulomatous uveitis due to trauma (more common) or surgery (less common) to one eye
Describe the pathophysiology of sympathetic ophthalmia
Thought to be secondary to development of an autoimmune reaction to ocular antigens which are exposed during the traumatic or surgical event - disadvantage of immune privilege in the eye
Which immune cells are believed to be the primary mediators for sympathetic ophthalmia?
T cells
How would you distinguish between the ‘exciting eye’ and the ‘sympathising eye’ in sympathetic ophthalmia?
Clinically both eyes appear the same - can only tell by the history
Which type of hypersensitivity is described as immediate and IgE mediated?
Type I
Which type of hypersensitivity involves direct cell killing (by macrophages/NK cells or complement + MAC)?
Type II
Which type of hypersensitivity is immune complex mediated?
Type III
Which type of hypersensitivity involves cell-mediated cytotoxicity?
Type IV
Give an ocular example of a type I hypersensitivity reaction
Acute allergic conjunctivitis +/- chemosis
Give an ocular example of a type II hypersensitivity reaction
Ocular cicatricial pemphigoid
What is ocular cicatricial pemphigoid?
Type of autoimmune conjunctivitis involving blistering and scarring of conjunctiva
Give an ocular example of a type III hypersensitivity reaction
Autoimmune corneal melting
Give an ocular example of a type IV hypersensitivity reaction
Corneal graft rejection
What causes corneal graft rejection?
Type IV hypersensitivity due to vascularisation of host cornea
Name two ocular side effects of steroids
Cataracts and steroid-induced glaucoma
List 3 factors that help to maintain immune privilege in corneal transplants
- Lack of immune cells (MHC molecules, Langerhans)
- Immunosuppressive molecules and inhibitory surface molecules
- Cornea lacks blood and lymph
