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Ophthalmology > Immunology and the Eye > Flashcards

Immunology and the Eye Flashcards

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
Q

How does the collagen arrangement of the cornea and sclera affect their appearance?

A

Cornea is clear due to fine arrangement of collagen

Sclera is white because collagen is less well organised

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26
Q

What are some features of the cornea and sclera?

A

Avascular, no lymphatics or lymphoid tissue, relative lack of antigen presenting cells

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27
Q

Where are antigen presenting cells found in the cornea?

A

Langerhans cells only present in the peripheral cornea

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28
Q

What is the immune environment of the cornea and sclera like?

A

Downregulated immune environment = immune privilege and angiogenic privilege

29
Q

What are some features of the lacrimal glands?

A

More plasma cells (IgA) and CD8+ T cells than conjunctivae, resting lymphoid cells very rarely observed

30
Q

How are T cells arranged in the lacrimal glands?

A

In small groups around intralobar ducts

31
Q

What is present in the drainage system of the lacrimal glands?

A

Diffuse lymphoid tissue and follicles (40-50%) in MALT

32
Q

Where is vitreous found?

A

In the fluid compartment of the eye

33
Q

What forms the blood-ocular barrier?

A

Choroid and retina = consists of tight junctions between cells of the vessel walls

34
Q

What is the purpose of the blood-ocular barrier?

A

Limits flow and transition of materials from blood into retina/outer ocular layers

35
Q

What is immune privilege?

A

Certain areas are able to tolerate introduction of antigens without eliciting an inflammatory immune response

36
Q

What are some areas of the body with immune privilege?

A

Brain/CNS, testes, placenta, eye

37
Q

What areas of the eye have immune privilege?

A

Cornea, anterior chamber, lens, vitreous cavity, subretinal space

38
Q

What mechanisms lead to ocular immune privilege?

A

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
Q

Where is the anterior chamber?

A

Space between the cornea and iris = usually filled with aqueous humour

40
Q

What induces anterior chamber associated immune deviation (ACAID)?

A

Placement of foreign antigen in anterior chamber = causes peripheral tolerance to ocular antigens by active mechanisms downregulating the immune response

41
Q

What are the immunological mechanisms of anterior chamber associated immune deviation?

A

Generation of primed CD4+ T cells and B cells

Inhibition of delayed type-hypersensitivity and cell-mediated immune responses

42
Q

What does the generation of primed CD4+ T cells and B cells produce?

A

Non-complement fixing antibodies

43
Q

What is the purpose of anterior chamber associated immune deviation?

A

Protects eye and visual axis from collateral damage form an immune response by suppressing a future potentially damaging response

44
Q

What is the basis of immune privilege?

A

Eye is ignorant to induction of non-self
Body is tolerant to presence of ocular antigens
Local environment within eye supports these

45
Q

What cause immunological ignorance in immune privilege?

A

Corneal cells have decreased expression of MHC I and don’t express MHC II, normal cornea lacks blood/lymphatic vessels

46
Q

How is the protection provided by immune privilege supported by inhibition?

A

Local factors in the eye inhibit components of the immune response

47
Q

What is sympathetic ophthalmia?

A

Rare, bilateral, granulomatous uveitis due to trauma (common) or surgery (rare) to one eye

48
Q

What is sympathetic ophthalmia secondary to?

A

Development of autoimmune reaction to ocular antigens exposed during the insult to the eye

49
Q

How does immune privilege work against the eye in sympathetic ophthalmia?

A

Immune responses occur at elevated rates

50
Q

What are the primary mediators of sympathetic ophthalmia?

A

T cells = initial wave of infiltrative wave composed of CD4+ helper T cells, later wave is CD8+ cytotoxic T cells

51
Q

How are the eyes referred to in sympathetic ophthalmia?

A

Injured eye is called the exciting eye, other eye is called the sympathetic eye

52
Q

How do the eyes appear in sympathetic ophthalmia?

A

Both eyes are clinically the same = inflammation of front chamber and vitreous gel, inflamed retina (retinitis/vasculitis), swelling under retina

53
Q

What is the pathogenesis of sympathetic ophthalmia?

A

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
Q

How is sympathetic ophthalmia treated?

A

Try to prevent it in penetrating injuries by stitching the globe back together = if damage extensive then eye may be removed

55
Q

When does the risk of sympathetic ophthalmia due to surgery increase?

A

After 4 or 5 operations to the one eye

56
Q

What are some hazards of immunity?

A

Recurrent infections, inadvertent injury to normal tissue, allergy, hypersensitivity, autoimmunity, cancer, graft/transplant rejection

57
Q

What are some ocular autoimmune diseases?

A

Autoimmune uveoretinitis = inflammation of uvea/retina
Dalen-Fuchs nodule = epithelial clusters in retinal layer
Keratoconjunctivitis sicca = dry eyes
Lens-induced uveitis
Sympathetic ophthalmia

58
Q

What are retinal antibodies associated with?

A

Common in retinopathy associated with cancer, infection or degenerative disease

59
Q

What do mast cells express on their surface?

A

Receptors for Fc region of IgE

60
Q

What happens when an allergen is introduced for the first time?

A

B cells produce antigen-specific IgE antibody = bind to foreign allergen

61
Q

Where do residual IgE antibodies bind once an allergen has been cleared after its first exposure?

A

They bind to mast cells via Fc receptors on mast cell surface

62
Q

What happens when an allergen is re-encountered?

A

Allergen binds to IgE = cross linkage of IgE bound to mast cells causing rupture of mast cell proteins (causes release of inflammatory mediators)

63
Q

What are the symptoms of acute allergic conjunctivitis?

A

Puffy swollen eyelids, inflamed eyes, chemosis, itch, watery eyes

64
Q

What are the effector cells in type 2 hypersensitivity reactions?

A

Macrophages/NK cells or complement

65
Q

What is ocular cicatricial pemphigoid?

A

Type 2 hypersensitivity reaction = subtype of mucous membrane pemphigoid

66
Q

What are the symptoms of ocular cicatricial pemphigoid?

A

Blistering lesions of eyes and lids, lid held open (ectropion), thickened upper lid, hazy cornea, extensive scarring may result

67
Q

What is autoimmune corneal melt?

A

Type 3 hypersensitivity reaction = opaque cornea which may perforate, treated with intensive steroids

68
Q

What are some features of corneal graft rejection?

A

Type 4 hypersensitivity reaction = occurs once graft comes into contact with vasculature, related to immune privilege

69
Q

What are some side effects of steroids that can affect the eye?

A

Cataracts or steroid-induced glaucoma

Ophthalmology (20 decks)

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