hypersensitivity/allergy Flashcards
what is hypersensitivity
hypersensitivity: innapropriate immune response as a result of autoimmunity or as side effect of responses to pathogens (immunopathology) or due to innocuous stimuli (allergy)
how many types of hypersensitivity are there
6 types: 1-6
describe type 1 hypersensitivity
type 1 hypersensitvity: IgE-mediated mast cell degranulation
classic allergy, (not all food allergies)
IgE has half life of 2.5 days in serum or 12 weeks if bound to mast cells
individuals with high levels of IgE more likely to have allergy, normal conc is 100ng/ml of serum
IgE is elevated in certain parasitic diseases, or hyper-IgE syndrome or allergy
class switching to IgE promoted by IL-4 and IL-13 from Th2 cells, is inhibited by interferon-gamma from Th1 cells
on mast cells there are Fcepsilon receptors, IgE is already bound normally, if many IgE molecules are stimulated via cross linking (one particle stimulating more than 1 antibody) then degranulation occurs
degranulation of granules causes increase in histamine and 5HT levels as they are stored in granules
inflammatory mediators stored in granules cause synthesis of TNFalpha, prostaglandins and leukotrienes
allergy testing: skin prick, exposed at different concentrations to allergen
how are type 1 allergens treated
corticosteroids; suppress transcription of proinflammatory genes
sodium chromoglycate: blocks mediator release from mast cells
anti-histamines
montelukast (leukotriene receptor antagonist)
immunotherapy: omalizumab (downregulates IgE)
repeated low dose of allergen
describe type 2 hypersensitivity
ype 2 hypersensitivity: cytotoxic antibody against cell surface antigens
antibody is made either against self or transplant, IgG binds to these cells and Fc region binds Fc receptors (FcRs) and activates macrophages or neutrophils leading to phagocytosis of the cell or target cell can be killed by antibody dependant cell mediated cytotoxicity involving NK cells or monocytes or eosinophils or complement is activated
what is haemolytic disease of newborn
due to a type 2 hypersensitivity:
haemolytic disease of the newborn due to rhesus incompatibility;
a baby between rhesus factor negative mother and positive father may lead to positive baby, this baby may then come in contact with mother in later stage of pregnancy and mother becomes sensitised. A second baby may be had by same mother which is also positive, IgG for anti rhesus factor positive crosses from mother to baby and causes haemolysis, does not occur any more much due to administration of prophylactics during 1st pregnancy of negative mothers
describe type 3 hypersensitivity
type 3: immune complex mediated
lots of antibody and antigen form immune complex which deposits onto tissue
macrophages and neutrophils, complement may be activated along with release of inflammatory mediators
can occur due to allergy such as farmers lung or pigeon fancier’s disease, some autoimmune disease and infections
describe type 4 hypersensitivity
type 4: delated type hypersensitivity/ T cell mediated hypersensitivity
works in different ways; involves TFN, interferon gamma, T cells and macrophages
examples; allergies such as allergic contact dermatitis, infections such as tuberculosis
patch tests are used to investigate allergic contact dermatitis
tuberculin skin test: small amount of tuberculosis bacterium is injected to skin intradermally, if no immune response is present shows no previous exposure
what is chronic local DTH reaction
is a type 4 hypersensitivity reaction:
chronic local DTH reaction:
continuous activation of T cells, accumulation of large number of macrophages, epitheloid cells
forms granulomas (large clump of T cells and macrophages)
describe type 5 hypersensitivity
type 5 hypersensitivity: stimulatory antibody against cell surface receptors
e.g. Graves’ disease
antibodies act stimulatory, stimulate cells to act in ways they should not (no killing)
describe type 6 hypersensitvities
innate hypersensitivities (type 6):
innapropriate activation of innate immune system
can occur due to sepsis or toxic shock syndrome
over activation of macrophages has been associated with many chronic diseases:
atherosclerosis, alzheimers, type 2 diabetes and “inflammaging”
inflammaging: levels of inflammatory cytokines is slightly raised from usual
