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Glossary of Hypersensitivity Diseases

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Four Classes of Hypersensitivity Diseases
Immediate
Antibody Mediated
Immune Complex Mediated
T-Cell Mediated
Mechanism of Immediate Hypersensitivity
antigen induces IgE/Th2
IgE binds Fc on mast cells and is cross-linked by antigen, then mast cell degranulation
Mast Cell Mediators
vasoactive amines, prostaglandins, leukotrienes, proteases, cytokines
Three classes of immediate hypersensitivity therapy
1) Inhibit Mast cell degranulation
2) Antagonize effects of mast cell mediators (antihistamines)
3) Reduce inflammation (corticosteroids)
Mechanism Antibody Mediated Diseases
failure of self-tolerance
antibodies vs. self antigens
cross reactive antibodies against microbial antigens
Example of Antibody Mediated Disease
Autoimmune Hemolytic Anemia
Mechanism of Immune Complex Mediated Disease
Antigen/Antibody complexes deposit in joints, vessels, kidney glomeruli
Examples of Immune Complex Diseases
Lupus, AGN
Mechanism of T-Cell Mediated Disease
CD4 Mediated - Delayed Type Hypersensitivity
CD8 Mediated - Host Cell Lysis
Example of T-Cell Mediated Disease
TB Granuloma formation
Target Antigen in Autoimmune Hemolytic Anemia
RBC membrane proteins (Rh, I Antigen), leads to opsonization and phagocytosis of RBC
Target Antigen in Autoimmune Thrombocytopenic Purpura
Platelet membrane proteins (gpIIb/IIIa); opsonization and phagocytosis of platelets, causes bleeding
Target Antigen in Pemphigus Vulgaris
Epidermal junction proteins: Ab mediated activation of proteases, causes bullae
Target Antigen in Goodpasture's Syndrome
Anti-GBM, basement membrane, in glomeruli and lung alveoli
Target Antigen in Acute Rheumatic Fever
Strep cell wall antigen, cross reacts with mycardial antigen, causes mycarditis/arthritis
Target Antigen in Myasthenia Gravis
acetycholine receptor, inhibits Ach binding, leads to muscle weakness/paralysis
Target Antigen in Grave's Disease
TSH Receptor, antibody mediated stimulation of TSH receptor, causes hyperthyroidism
Target Antigen in Pernicious Anemia
Ab neutralize intrinsic factor of gastric parietal cells, decreased B12 absorption, leads to abnl erythropoeiesis and anemia
Primary Mediators of Type I reactions
Histamine, proteases, chemokines, heparin
Secondary mediators of Type I reactions
PAF, leukotrienes, prostaglandins, bradykinins, other cytokines

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