HYPERSENSITIVITY REACTIONS
TYPE I: IMMEDIATE
These reaction are those that involve antigens that react with IgE bound to tissue mast cells or basophils. Activation of the mast cell results in the release of large amounts of pharmachologically active substances. These reactions are rapid (hence immediate) and if injected into the skin a "wheel and flare" reaction can be seen within five to ten minutes. Most antigens stimulating IgE are either inhaled or ingested. A perfect example of the inhaled antigen is ragweed pollen. The IgE production requires helper T cells and T-cell-derived cytokines. IL-4 and IL-13 stimulate IgE production while IFN-γ is inhibiting. Many factors regulate the balance between help and suppression, including route of administration, physical nature of the substance, and the genetic background of either animals or humans. In the latter, there s a family tendency to these reactions but exact genetic factors are still ill defined.
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