Antigens cross-linking

Type I reactions occur when the drug or its bound hapten incites an IgE antibody response. IgE binds to high-affinity receptors on mast cells and basophils. When the original antigen cross-links the cell-bound IgE, the effector cell releases enormous amounts of preformed mediators, producing the... 

Figure 6.31 The basis of type I hypersensitivity reactions. The antigens cross-link with IgE antibodies, which are attached to mast cells.

Figure 33.4. Antigen Cross-Linking. Because IgG molecules include two antigen-binding sites, antibodies can crosslink multivalent antigens such as viral surfaces.

Histamine is a low-molecular-weight amine compound formed by decarboxylation of histidine and is stored in basophil and mast cell granules. The release of histamine from these cells is triggered by antigen cross-linking IgE bound to specific receptors on the surface membranes of mast cells and basophils. The tissue effects of histamine are evident within 1 to 2 minutes, but it is rapidly metabolized within 10 to 15 minutes. The major effects of histamine on target tissues include increased capillary permeability, contraction of bronchial and vascular smooth muscle, and hypersecretion of mucus glands. 

Figure 1. Sequence of events in the secretion of mediators from mast cells or basophil leukocytes. IgE antibody (Y) binds to the cell membrane at specific receptor sites to sensitize the ceU. Antigen cross-linking IgE molecules provide a membrane signal to the cell which sets in motion a chain of biochemical events. The membrane surrounding the granules (%), which contains the mediators, fuses with the cell membrane (exocytosis) to allow the mediators to escape into the surrounding medium. The granule matrix behaves as an ion-exchange resin releasing histamine and taking up Na...

Antigen Cross-linking Antigen- Poly-acrylamide Increased [8]... 

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