Hypersensitivity - Type I Flashcards
What are the principal cells and antibodies that mediate Type I Hypersensitivity?
APC w/ allergen on MHC-II and B7 costim bind to Naive CD4+ cell’s CD4 and CD28—>IL-4 floatin’ around—>maturation into Th2-cell—>induce B-cell (plasma cell) class ∆ing—>”IgE (usually); other immunoglobulins e.g. IgG4
Which Hypsensitivity Types are Ab-mediated? Which are cell-mediated?
I, II and III are Ab-mediated. IV is cell-mediated
Define atopy
presence of specific IgE directed against environmental allergens
Name 3 majors processes in anaphylaxis
dilation and leakage of post-capillary venules (causing edema, life-threatening hypotension and cardiovascular collapse) and constriction of airway smooth muscles, (bronchoconstriction, which can result in hypoxia and death).
Contrast first and second exposures in Type 1.
First exposure = sensitization where IgE “arms” the FcER1 receptors and basophils and mast cells.
2nd exposure: allergen cross-links these and causes release of immediate hypersensitivity mediators
Define mast cell role in Type 1
releases granules full of mediators when allergens bind the allergen-specific IgEs that are residing in its FcεR1 receptors
histamine
most common vasoactive amine; stored in granules of mast cells and basophils; causes increase vasc permeability, (Abbas: also vasodilation), SMM constriction and incr mucous prod in goblet cells, via H1 receptors.
increases gastric secretions via H2 receptors (target of some heartburn meds!)
basophil
Orig. in marrow and circulate in blood responding to chemotactic stim.; have FcεR1 receptors; release mediators
IgE
Ab that mediates Type I; plasma [IgE] incr in atopic individuals; made predom. in GI and resp. epith. plasma cells; binds FcεR1 on: mast cells, eosinophils, basophils, lymphocytes and monocytes; dunno what it’s for totally, think defense against helminthes and some protozoans
you only need tiny bit (10^-10 IgEs will sat. 1/2 all FcεR1s)
FcεR
receptor for IgE; found on mast cells, eosinophils, basophils, lymphocytes and monocytes
prostaglandin D2
lipid mediator that causes periph. vasodilation, coronary vasoconstriction, bronchoconstriction, inhibits platelet agg, and attracts neutrophils; made in response to cross-linking of IgE in FcεR on surface of ?basophils and ?mast cells
allergen
an antigen that causes a Type I hypersensitivity rxn in an atopic pt.
hyposensitization
(a.k.a. immunotherapy) tx for atopic pts; give grad. incr. doses of allergen either subQ or SL; idea: will incr IgG and IgA to allergen
lekotriene
lipid mediator (from arachadonic acid 1°ly): bronchoconstr., vasodilator and incr vasc perm —> edema; incr mucous, constriction coronary and cerebral aa., decr contractility and incr gastric acidity
sensitization
initial exposure to allergen that causes initial generation of IgE against allergen and then coating of FcεR-bearing cells with that IgE