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Ophthalmology > Immunology and the Eye > Flashcards

Immunology and the Eye Flashcards

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1
Q

What is the purpose of the immune system?

A

Identify and eliminate harmful substances = does this by distinguishing self from no-self and by identifying danger signals (e.g inflammatory mediators)

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2
Q

What are the types of immune response?

A 
Innate = 1st line response, non-specific (physical barrier, commensal etc)
Adaptive = pathogen=specific, acquired through expose, has memory
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3
Q

What occurs 0-4 hrs after exposure to an antigen?

A

Immediate innate response = complement, macrophages, mast cells, inflammation, antimicrobial proteins

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4
Q

What occurs 4-96hrs after exposure to an antigen?

A

Early innate immune response = recruitment and activation of phagocytes, inflammation

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5
Q

What occurs >96hrs after exposure to an antigen?

A

Late adaptive response

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6
Q

What distinguishes the eye from other parts of the body in terms of its innate immunity?

A

It doesn’t have any skin as a protective barrier and has few commensal bacteria

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7
Q

What are the main elements of the innate immunity of the eye?

A

Blink reflex = involved in clearing pathogens, limits exposure/size of eye by closing it
Tears = flush away pathogens or dirt

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8
Q

What are the three layers present in tears?

A

Outside lipid layer, middle aqueous layer, inner anti-adhesive mucin layer

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9
Q

What does the mucin layer of tears do?

A

Prevents pathogens sticking to the eye

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10
Q

What are some chemicals present in tears?

A

Lysozyme = destroys bacterial cell wall (gram -ve/fungi)
Lactoferrin/transferrin = gram +ve bacteria
Tear lipids = antibacterial to cell membrane, scavenger
Angiogenin = antimicrobial effect in tear film
IgA = prevents attachment
IL-6, IL-8, MIP = recruit leucocytes
Complement

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11
Q

What immune cells are present in tears?

A

Neutrophils, macrophages, conjunctival mast cells

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12
Q

What are some features of neutrophils?

A

Attracted by chemotaxis = scavengers that release free radicals and antimicrobial enzymes

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13
Q

What are some features of macrophages?

A

Carry out phagocytosis of damaged cells and help trigger adaptive immunity (antigen presenting cells)

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14
Q

What are conjunctival mast cells?

A

Vasoactive mediators = control dilation/contraction of blood vessels

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15
Q

What is the role of antigen presenting cells?

A

Recognise issue and trigger adaptive response = dendritic cells, B cells, macrophages

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16
Q

What is the purpose of lymphatic drainage?

A

Allows antigen presenting cells to take information to lymph nodes to alert the rest of the immune system

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17
Q

What are some examples of immune effector cells?

A

CD4+ T cells, CD8+ T cells, B cells

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18
Q

What are Langerhans cells?

A

Type of macrophage = main antigen presenting cells of the external eye, rich in class II MHC molecules

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19
Q

Where in the eye are Langerhans cells found?

A

Abundant at the corneo-scleral junction, less in peripheral cornea, absent from central 1/3 of cornea

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20
Q

What is the only part of the eye that has lymphatic drainage?

A

The conjunctivae = specialised venules for regulated migration of lymphoid cells

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21
Q

What is present in all conjunctival zones?

A

diffuse lymphoid populations = CD4+/CD8+ T cells, IgA secreting plasma cells
Small number of commensal bacteria

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22
Q

What are the antigen presenting cells of the conjunctivae?

A

Dendritic cells

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23
Q

What is the only part of the eye with MALT tissue?

A

Conjunctivae = macrophages, Langerhans cells and mast cells frequent (neutrophils/eosinophils emigrate there only when recruited)

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24
Q

What do the cornea and the sclera form together?

A

Collectively form a tough collagen coat

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25
How does the collagen arrangement of the cornea and sclera affect their appearance?
Cornea is clear due to fine arrangement of collagen | Sclera is white because collagen is less well organised
26
What are some features of the cornea and sclera?
Avascular, no lymphatics or lymphoid tissue, relative lack of antigen presenting cells
27
Where are antigen presenting cells found in the cornea?
Langerhans cells only present in the peripheral cornea
28
What is the immune environment of the cornea and sclera like?
Downregulated immune environment = immune privilege and angiogenic privilege
29
What are some features of the lacrimal glands?
More plasma cells (IgA) and CD8+ T cells than conjunctivae, resting lymphoid cells very rarely observed
30
How are T cells arranged in the lacrimal glands?
In small groups around intralobar ducts
31
What is present in the drainage system of the lacrimal glands?
Diffuse lymphoid tissue and follicles (40-50%) in MALT
32
Where is vitreous found?
In the fluid compartment of the eye
33
What forms the blood-ocular barrier?
Choroid and retina = consists of tight junctions between cells of the vessel walls
34
What is the purpose of the blood-ocular barrier?
Limits flow and transition of materials from blood into retina/outer ocular layers
35
What is immune privilege?
Certain areas are able to tolerate introduction of antigens without eliciting an inflammatory immune response
36
What are some areas of the body with immune privilege?
Brain/CNS, testes, placenta, eye
37
What areas of the eye have immune privilege?
Cornea, anterior chamber, lens, vitreous cavity, subretinal space
38
What mechanisms lead to ocular immune privilege?
Blood-ocular barrier Lack of direct lymphatic drainage Microenvironment rich in immunosuppressive molecules and inhibitory cell surface molecules Anterior chamber associated immune deviation (ACAID
39
Where is the anterior chamber?
Space between the cornea and iris = usually filled with aqueous humour
40
What induces anterior chamber associated immune deviation (ACAID)?
Placement of foreign antigen in anterior chamber = causes peripheral tolerance to ocular antigens by active mechanisms downregulating the immune response
41
What are the immunological mechanisms of anterior chamber associated immune deviation?
Generation of primed CD4+ T cells and B cells | Inhibition of delayed type-hypersensitivity and cell-mediated immune responses
42
What does the generation of primed CD4+ T cells and B cells produce?
Non-complement fixing antibodies
43
What is the purpose of anterior chamber associated immune deviation?
Protects eye and visual axis from collateral damage form an immune response by suppressing a future potentially damaging response
44
What is the basis of immune privilege?
Eye is ignorant to induction of non-self Body is tolerant to presence of ocular antigens Local environment within eye supports these
45
What cause immunological ignorance in immune privilege?
Corneal cells have decreased expression of MHC I and don't express MHC II, normal cornea lacks blood/lymphatic vessels
46
How is the protection provided by immune privilege supported by inhibition?
Local factors in the eye inhibit components of the immune response
47
What is sympathetic ophthalmia?
Rare, bilateral, granulomatous uveitis due to trauma (common) or surgery (rare) to one eye
48
What is sympathetic ophthalmia secondary to?
Development of autoimmune reaction to ocular antigens exposed during the insult to the eye
49
How does immune privilege work against the eye in sympathetic ophthalmia?
Immune responses occur at elevated rates
50
What are the primary mediators of sympathetic ophthalmia?
T cells = initial wave of infiltrative wave composed of CD4+ helper T cells, later wave is CD8+ cytotoxic T cells
51
How are the eyes referred to in sympathetic ophthalmia?
Injured eye is called the exciting eye, other eye is called the sympathetic eye
52
How do the eyes appear in sympathetic ophthalmia?
Both eyes are clinically the same = inflammation of front chamber and vitreous gel, inflamed retina (retinitis/vasculitis), swelling under retina
53
What is the pathogenesis of sympathetic ophthalmia?
Injury to one eye causes release of sequestered intra-ocular antigens Antigens carried to lymph nodes = activates T cells Immune system isn't specific so sends activated T cells to both eyes
54
How is sympathetic ophthalmia treated?
Try to prevent it in penetrating injuries by stitching the globe back together = if damage extensive then eye may be removed
55
When does the risk of sympathetic ophthalmia due to surgery increase?
After 4 or 5 operations to the one eye
56
What are some hazards of immunity?
Recurrent infections, inadvertent injury to normal tissue, allergy, hypersensitivity, autoimmunity, cancer, graft/transplant rejection
57
What are some ocular autoimmune diseases?
Autoimmune uveoretinitis = inflammation of uvea/retina Dalen-Fuchs nodule = epithelial clusters in retinal layer Keratoconjunctivitis sicca = dry eyes Lens-induced uveitis Sympathetic ophthalmia
58
What are retinal antibodies associated with?
Common in retinopathy associated with cancer, infection or degenerative disease
59
What do mast cells express on their surface?
Receptors for Fc region of IgE
60
What happens when an allergen is introduced for the first time?
B cells produce antigen-specific IgE antibody = bind to foreign allergen
61
Where do residual IgE antibodies bind once an allergen has been cleared after its first exposure?
They bind to mast cells via Fc receptors on mast cell surface
62
What happens when an allergen is re-encountered?
Allergen binds to IgE = cross linkage of IgE bound to mast cells causing rupture of mast cell proteins (causes release of inflammatory mediators)
63
What are the symptoms of acute allergic conjunctivitis?
Puffy swollen eyelids, inflamed eyes, chemosis, itch, watery eyes
64
What are the effector cells in type 2 hypersensitivity reactions?
Macrophages/NK cells or complement
65
What is ocular cicatricial pemphigoid?
Type 2 hypersensitivity reaction = subtype of mucous membrane pemphigoid
66
What are the symptoms of ocular cicatricial pemphigoid?
Blistering lesions of eyes and lids, lid held open (ectropion), thickened upper lid, hazy cornea, extensive scarring may result
67
What is autoimmune corneal melt?
Type 3 hypersensitivity reaction = opaque cornea which may perforate, treated with intensive steroids
68
What are some features of corneal graft rejection?
Type 4 hypersensitivity reaction = occurs once graft comes into contact with vasculature, related to immune privilege
69
What are some side effects of steroids that can affect the eye?
Cataracts or steroid-induced glaucoma

Ophthalmology (20 decks)

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