Hypersensitivity (Schein) Flashcards
Mast cell stored substances
- Histamine
- Serotonin
- Eosinophil/neutrophil chemotactic factors
- Protease
Mast cell synthesized substances
- leukotrienes
- prostoglandins
- Bradykinin
- cytokines
RAST Testing (Radioallergoabsorbent)
Detects serum levels of IgE. Antigen coupled to beads, serum added, IgE binds beads. Add labeled anti-IgE, measured to quantify IgE present.
Allergy Shots
Give increasing doses of allergen over time. Causes class switching (IgE–>IgG/A) and increased Treg (suppress TH2, which make IgE). IgG/A bind antigen instead of IgE in future, preventing hypersensitivity type I reaction.
Type II Hypersensitivity
- Hours
- Antibody mediated
- IgM/G bind antigen, act to opsonize for macrophage/neutrophil phagocytosis. Also activates complement system and ADCC (NK cells)
- Includes transfusion reactions, erythroblastosis fetalis, drug induced hemolytic anemia
ADCC (Antibody-Dependent Cell-mediated Cytotoxicity)
- Target cell coated with antibodies, lysed by cytolytic effector cell (NK cell, macrophage, neutrophil)
- Requires prior antibody response
Type I Hypersensitivity
- Occurs immediately (within minutes)
- IgE mediated
- Allergy, asthma, atopy
Type III Hypersensitivity
-4-12 hours
-Immune complex disease - caused by circulating antibody(IgG)-antigen complexes, get lodged in filtering organs and small blood vessels
-
Arthus Reaction
Type III Hypersensitivity ex- Localized deposition of immune complexes causes mast cell activation (IgG), neutrophils, complement (C3a/C5a).
-Localized ex of type III. Like if give vaccine in skin and antigen accumulates, complex forms at site. Unlike systemic type III
Localized Type III Hypersensitivity Reactions
- local vasculitis
- bug bites
- Drugs/vaccines
- Farmer’s Lung (inhale bacterial spores/fungi, intrapulmonary)
Systemic Type III Hypersensitivity reactions
- Serum Sickness
- Rheumatoid arthritis (immune complexes deposit in kidneys, joints)
- Lupus
Serum Sickness
ex: get horse antiserum as treatment for snakebite. Produce antibodies against since it’s foreign. If exposed again, antibodies bind, form immune complex, causing type III hypersensitivity reaction
Type IV Hypersensitivity
- Delayed (2-3 days)
- Mediated by TH1 cells, antibody dependent
- Mechanism: In subsequent exposure to an antigen, memory TH1 cells recognize antigen, proliferate, secrete cytokines, recruit macrophages
- Ex: tuberculin test (give antigen, reaction appears after 2-3 days indicates prior TB infection)
- Allergy to metals
- Organ transplant rejection
- Poison ivy
Remembering Hypersensitivity Reactions- ABCD
A- Allergic
B- antiBody
C- Complex
D- Delayed
