hypersensitivity and autoimmunity week 5 Flashcards
who has the potential to develop an autoimmune disease
everyone
what are hypersensitivity responses
harmful immune response that may produce tissue injury and cause serious disease
- 4 categories: I, II, III, IV, (V)
what antibodies are associated with type I
IgE
- allergy
what antibodies are associated with type II and III
IgG
what cells are associated with type IV
T helper 1/17
T helper 2
CTL- cytotoxic T cell
what happens in type I
- first exposure to antigen
- activation of T follicular helper cells (IL-4 producing) and stimulation of IgE class switching in B cells
- production of IgE
- binding of IgE to FcRI receptor on mast cells
- repeated exposure to allergen
- activation of mast cell, release of mediators
- mediators: vasoactive amines, lipid mediators (immediate hypersensitivity reaction after repeat exposure) and cytokines (late phase reaction, 2-4 hours after repeat exposure)
what are the effects of type I
mast cell: vasodilation, vascular leak, broncho-constriction, intestinal hyper motility, inflammation, tissue damage
eosinophil: killing of parasites and host cells, tissue damage
what happens in immediate phase of type I
- IgE mediated effects
- vasodilation, oedema and vascular congestion
what happens in the late reaction of type I
eosinophil, neutrophil and T cell infiltrates
what is atopy
predisposition to allergy
associated with high levels of IgE
what is type II
injury caused by anti-tissue antibody
- antibody deposition in extracellular matrix, they can interact via Fc gamma receptor (reacts with IgG)
- this leads to mediated recruitment and activation of inflammatory cells such as neutrophils and macrophages
- these cells start releasing lysosomal enzymes and reactive oxygen species which will generate tissue injury and pro-inflammatory response
what is type III
immune complex-mediated tissue injury
- circulating immune complexes (can contain thousands of antibodies)
- complement and Fc receptors result in mediated recruitment and activation of inflammatory cells (neutrophils release lysosomal enzymes, reactive oxygen species)
- this results in vasculitis if site of deposition in blood vessel
what response is possibly type II and V
abnormal physiological responses without cell/tissue injury
- antibody stimulates receptor without ligand
- antibody inhibits binding of ligand to receptor
what is type IV
2 types:
cytokine-mediated inflammation
- CD4+ on T cell bound to tissue antigen on macrophage
- CD8+ on T cell is bound to receptor on tissue
- both of these T cells release cytokines which results in inflammation and tissue injury
T cell-mediated cytotoxicity
- CD8+ bound to receptors on tissue
- this results in cell killing and injury
what is immune tolerance
- state of unresponsiveness to specific antigen
- antigens can be self or foreign
- prevents adaptive responses that are damaging
- can be exploited by microbes and tumours
