Hypersentivity disorders refer to excessive or inappropriate activation of the immune system although activation of the immun system normally leads to the production of antibodies and Tcell responses that protect the body against attack by microorganizms, it is also capable of causing tissue injury and disease.
Disorders caused by immune responses are collectively referred as hypersensitivity reactions.
| TYPE I Immediate (allergic or Anaphylaxis): | IgE mediated, antigen reacts to IgE on ast cells leading to histamine release Examples: seasonal rhinitis, food allergy |
| TYPE II Antibody mediated (cytotoxic): | IgM or IgG mediated. IgG’s react with antigen leading to complement activation causing lysis of the cell. Examples: drug reactions, hemolytic reactions Antibody-Dependent Cell-Mediated Cytotoxicity Good Pastures Noncytotoxic - myasthenia gravis |
| TYPE III Immune complex mediated (immune complex reaction): | IgM or IgG mediated, IG’s bind with antigen forming an Ab/Ag complex. Complex is deposited in tissues and the inflammatory response is initiated Examples: autoimmune disease such as lupus and Rheumatoid arthritis |
| TYPE IV Cell mediated (delayed hypersensitivity): | T-lymphocyte mediated, exposure to previously sensitized antigen, T-cells release lymphokines leading to cell lysis Examples: TB test, contact dermatitis |
Mediators
Histamine à bronchoconstriction, mucus secretion, vasodilatation, vascular permeability
Acetylcholine and kinins àsmooth muscle constriction in airways, vasodilation, Kinins cause of pain, directly
Leukotrienes and prostaglandins à produce the same effects on a prolonged scale, Leukotrienes initate inflammatory response
Cytokines and chemotactic factors à attract more WBCs to contribute to the response
Iatrogenic - adverse effects or complications caused by or resulting from medical treatment
Neutrophils – soldiers first primary phagocyte
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