Type III Hypersensitivity Flashcards
What are the two mechanisms of type III reactions?
After complement activated against deposited small immune complexes:
1) Production of anaphylatoxins (C3a, C4a, and C5a) -> Mast cell degranulation -> increased vascular permeability
2) Neutrophil-mediated phagocytosis of small immune complexes fails due to basement membrane; lytic enzymes degrade membrane
Where does serum sickness occur, what causes it, and what are its symptoms?
1) Diptheria patients treated w/ anti-diphtheria horse serum
2) A type III hypersensitivity reaction (agains horse serum)
3) Fever, rashes due to vasculitis, arthritis, glomerulonephritis
What are 5 examples of Type III Hypersensitivity?
1) Systemic lupus erythematosus
2) Generalized discoid lupus erythematosus
3) Feline leukemia
4) C3 deficiency
5) Rheumatoid arthritis
What causes systemic lupus erytematosus?
Type III reaction due to antibodies against self-DNA, nucleoprotein, and histones
What are the clinical signs of systemic lupus erythematosus?
1) Rashes (due to vasculitis)
2) Glomerulonephritis
- Increases glomerular permeability, causing albumin to enter in urine
3) Arthritis
What is the difference between systemic and generalized discoid lupus erythematosus?
Generalized discoid:
1) Involves skin only
2) Tests negative for antinuclear antibodies
Type III hypersensitivity causes which symptom of feline leukemia?
Glomerulonephritis
What causes rheumatoid arthritis?
IgM autoantibody (rheumatoid factor) against IgG -> type III reaction
Arthus reaction
Test for type III reaction
- Produce localized reaction intradermally or subcutaneously
- Positive if vasculitis with necrosis
What are 2 examples of localized Type III Hypersensitivity?
- Pneumonitis in cattle
2. General discoid lupus erythromatosus in dogs
The most important effector cells of pneumonitis mediated by type III hypersensitivity are:
Neutrophils
