Immunology Flashcards
What are the solutions the bodies immune system has developed due to the fact they eye has no physical barrier and not really any commensal bacteria ?
- Blink reflex
- Physical and chemical properties of eye surface
- Limit exposure/size
How does the blink reflex and physical properties of the eye help protect it ?
TEARS – PHYSICAL and blink reflex
- Help flush things out the eye
- Also provide a mucous layer which helps prevent things sticking onto the eye
What are some of the chemical properties which help protect the eye?
- Lysozyme: v. gram –ve bacteria, fungi (destroy bacteria cell wall)
- Lactoferrin and transferrin: v. gram +ve bacteria
- Tear lipids: antibacterial to cell membranes/scavenger of bacterial products
- Angiogenin: antimicrobial effect within tear film
- Secretory IgA: prevents attachment
- Complement
- IL-6, IL-8, MIP: antimicrobial molecules that recruit leucocytes
What the the main immune cells in the eye ?
- Neutrophils
- Macrophages
- Conjunctival mast cells
What are the 3 main requirements of the adaptive immune system ?
- Antigen presenting cells (APC = dendritic cells, B cells, macrophages)
- Lymphatic drainage to lymph node
- Variety of effector cells (incl. CD4+ T cells, CD8+ T cells, B cells)
What is the main APC for the external eye and where are they mainly found ?
- Langerhans Cells (type of macrophage)
- Found mainly at the corneo-scleral limbus (junction between the cornea and sclera)
What is the only part of the eye with lymphatic drainage ?
The conjunctiva
Define what is meant by immune privilege
It is where a site is able to tolerate the introduction of antigens without eliciting an inflammatory immune response
What areas in the eye have immune privilege ?
- Cornea
- Anterior chamber
- Lens
- Vitreous cavity
- Subretinal space
What are some of the factors which contribute to immune privilege ?
- Blood-tissue barrier and a lack of direct lymphatic drainage
- Ocular microenvironment is rich in immunosuppressive molecules and inhibitory cell surface molecules that influence the reactivity of immune cells
- Anterior chamber-associated immune deviation (ACAID)
What does anterior chamber associated immune deviation do ?
Protects the eye from collateral damage by suppressing a future potentially damaging response to infection.
Through:
- Generation of primed CD4+ T and B cells that produce non-complement-fixing antibodies
- Inhibition of delayed-type hypersensitivity (CD4+ Th1) and B cells that secrete complement-fixing antibodies (inhibition of a cell-mediated immune response)
What is sympathetic ophthalmia ?
Development of an autoimmune reaction to ocular antigens: exposed during a traumatic or surgical event
Describe the pathogenesis of sympathetic ophthalmia
- Initialy exposed to intraocular antigens
- Followed by Initial wave of infiltrative cells composed of CD4+ helper T cells in both eyes
- Then followed by a secondary wave of CD8+ cytotoxic T cells
What are some of the conditions which can occur due to problems with the immune system ?
- Recurrent infections
- Inadvertent injury to normal host tissues
- Allergy
- Hypersensitivity reactions
- Autoimmune disease
- Cancer
- Transplant/graft rejection
What are the main regions on the antibiody and mast cell which interact with each other ?
You have the Fc receptor on the mast cell which beinds to the Fc region on the antibody
The arms of the antibody are the antigen specific regions
Describe the process of how Type I hypersensitivity occurs
- On encounter with allergen, B cells produce antigen-specific IgE antibody
- Allergen is cleared
- Residual IgE antibodies bind to circulating mast cells
- Then on re-encouter with allergen the primed mast cells release vasoactive mediators (type I hypersensitivity reaction)
Give an example of a type I hypersensitivity reaction affecting the eye ?
Allergic conjunctivitis - eye appears very watery and puffy
What are the cells which are involved in Type II hypersensitivity reactions ?
- Macrophages/natural killer (NK) cells
- Complement (membrane attack complex)
Known as the antibody mediated cytotoxicity (direct-cell killing)
Give an example of a type II hypersensitivity reaction affecting the eye
Ocular cicatricial pemphigoid - Type of autoimmune conjunctivitis, blistering and scarring of conjunctiva
Describe type III hypersensitivity reactions
Immune complex mediated:
- Excess antigen present
- Antibodies then bind to the antigens forming immune complexes of varying sizes
- Large immune complexes can be cleared but smaller complexes cannot be cleared so easily
- This results in the smaller immune complexes depositing intosmall blood vessels, joints, and glomeruli, causing symptoms
- The reaction can take hours, days, or even weeks to develop
Give an example of an type III hypersensitivity reaction
Autoimmune corneal melting
Describe type IV hypersensitvity
Delayed type hypersensitivity often called cell-mediated cytotoxicity
- CD4+ helper T cells recognize antigen in a complex with MHC II major on the surface of antigen-presenting cells.
- CD4+ T cells secrete IL-2 and interferon gamma, inducing the further release of other Th1 cytokines, thus mediating the immune response.
- Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.
Give an example of type IV hypersensitivty reactions in the eye
Corneal graft rejection
