13) Hypersensitivity Flashcards
define hypersensitivity rxn
exaggerated/inappropriate immune response with damage to host
basic mechanism of TI HS rxn
IgE mediated
binds to masts and basos
histamine release
general sx of TI HS rxn
rhinitis
asthma
anaphylaxis
basic mechanism of TII HS rxn
IgG/IgM binds to cell and activates complement
immediate HS rxn (within minutes)
type I
cytotoxic HS rxn
type II
immune complex HS rxn
type III
TIII HS rxn timeframe
within hours
TIV HS rxn timeframe
1-2 days
cell mediated/delayed type HS rxn
type IV
basic mechanism of TIII HS rxn
IgG or IgM - Ag complexes accumulate in blood/tissues
granulocytes release damaging enzymes
basic mechanism of TIV HS rxn
T-cell cytokines activate macros, causing damage
3 phases of TI HS rxn
- sensitization
- activation
- effector response
first exposure to Ag, IgE attaches to masts/basos
sensitization stage (type I)
reaginic Ab
IgE
stimultes/suppresses IgE production
stimulates: IL-4
suppresses: IFN-𝛾
begins activation phase of TI HS rxn
2 forms
challenge/2nd exposure to Ag
cutaneous injection
IV/parenteral injection
wheal & flare rxn part of type —- HS rxn
I
wheal & flare peaks in —— mins
sx
10-15
erythema
edema
“hives”
required for Ig to cause degranulation
2 Fc receptors crosslinked by Ag
triggers of mast cell degran
- IgE
- C3a, C5a
- drugs
- lectins
- extreme heat & cold
control mechanism for mast cell degran (TI HS rxn activation phase)
- adenylate cyclase converts ATP to cAMP during degranulation
- sustained increase in intracellular cAMP slows or stops degranulation
2 types of mediators involved in TI HS rxn effector phase
- preformed mediators - stores in granules
- newly-synthesized mediators
main preformed mediator
histamine
storage of histamine
electrostatic interaction with heparin
histamine binding sites
H1 (smooth muscle, endothelials)
H2 (mucosal membranes)
effects of histamine
- smooth muscle constriction
- vascular permeability
- release of stomach acid
antihistamines block —–
H1