Hypersensitivity Flashcards
Hypersensitivity Reactions
an exaggerated response to a harmless antigen
reaction dependent on host’s response
Sensitization
hypersensitivity reactions that occur in subjects previously exposed to Ag who have developed immune response
Allergy
2 forms of hypersensitivity can occur in response to different types of Ag
Type 1 - immediate type
type 4- delayed type
Type 1 hypersensitivity reaction
immediate hypersensitivity reaction (2-30 minutes)
mediated by IgE antibodies!!
Step 1 of Type 1 hypersensitivity
allergen is presented to CD4+ (Th2 subtype)
Step 2 of Type 1 hypersensitivity
stimulates B cell production of IgE Abs
produces a large amount of IgE in response to a small concentration of antigen
Step 3 of Type 1 hypersensitivity
Sensitization phase!
IgE Abs attach at the Fc end to mast cells of the tissues & basophils in the blood
IgE remains dormant attached to these cells
IgE serves as an antigen receptor
Step 4 of Type 1 hypersensitivity
when exposed to allergen a second time
antigens combine with IgE Abs on the surface of mast cells & basophils & release histamines & serotonins
Clinical Manifestations of Type 1 hypersensitivity
can be localized & systemic
Allergic Asthma
type 1 :
coughing, wheezing, shortness of breath etc
Atopic Dermatitis
type 1:
itchy, red skin rash,
chronic lesions w/ thickened skin may develop
Urticaria
Type 1:
commonly associated with allergies to latex, foods, drugs
widespread, itchy, white areas surrounded by redness ‘wheal & flare’
Gastrointestinal Reactions
Type 1:
usually associated with food allergies, nausea, vomiting, abdominal pain, etc
Systemic Anaphylaxis
Type 1:
potentially life-threatening
seconds or minutes, can involve multiple organ systems
Type 1 testing
- in vivo methods - direct skin testing
2. in vitro methods - lab testing serum of total IgE
In Vitro Allergy test
for type 1 hypersensitivity:
- radioimmunosorbent test RIST- total IgE
- radioallergosorbent test RAST - allergen specific IgE
Type 1 treatment
avoid allergen
block allergen response
immunotherapy - desensitization or allergy shots
Type 2 hypersensitivity
reaction caused by the reaction of IgG and IgM with cells and tissues
antibody dependent & complement mediated
Type 2 Clinical Manifestations
- transfusion reactions
- hemolytic disease of the newborn
- hemolytic anemias - autoimmune
Hemolytic transfusion reaction
type 2 hypersensitivity
massive complement activation, hemolysis, shock, death etc etc
Type 2 testing
Direct Antiglobulin test (DAT)
agglutination is positive
Type 3 hypersensitivity
immune complex formation
IgG or IgM antibodies - complement mediated
Step 1 of type 3 hypersensitivity
soluble antigen combines with soluble antibody, immune complexes are formed & precipiate out of the serum
Step 2 of type 3 hypersensitivity
in the tissues the immune complexes bind complement
step 3 of type 3 hypersensitivity
complement activation results in histamine/cytokine activation
step 4 of type 3 hypersensitivity
neutrophils migrate to site & release granules causing chronic inflammation & tissue destruction
Type 3 clinical manifestations
lupus,
post streptoccoal glomerulnephritis,
reactive arthritis
farmer’s lung
Type 3 testing
look for immune complex (Ig) deposition in tissues with immunohistochemistry
Type 4 hypsersensitivity
delayed hypersensitivity (2-3 days)
no antibody involved
mediated by CD4+ Th1 T cells & CD8+ cells
Sensitization phase of type 4 hypersensitivity
- antigen contact
- 1-2 weeks after initial contact: antigen processed & presented to antigen specific Th cells & they then activate & proliferate
these cells are called delayed-type hypersensitivity T cells
Effector phase of type 4 hypersensitivity
next antigen exposure, production of variety of cytokines & chemokines
attract monocytes & PMNs
inflammatory response follows, results in tissue damage, granulomas, & necrosis
Contact Dermatitis
Type 4:
skin reaction caused by contact w/ a variety of agents
Hypersensitivity Pneumonitis
Type 4:
inhalation of allergen, most cases occupational - farmer’s lung etc
M. TB screening test (Mantoux test)
Type 4 reaction
positive result suggests an individual has been exposed
