FRANCIS LEROY & M. MARTINACHE, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY & M. MARTINACHE, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Type I hypersensitivity response, animation. This is an allergic response caused by reexposure to a specific allergen, or antigen (red). The first time the antigen is encountered it is captured by an antigen presenting cell (left), which presents it to B lymphocytes (light blue) and CD4 T helper lymphocytes (orange). These are types of white blood cell. The T helper lymphocytes stimulate the B lymphocytes to produce immunoglobulin E (IgE) antibodies (Y-shaped) that specifically bind the antigen. These antibodies attach to mast cells (right), sensitising them. The next time that the antigen is encountered it is bound by antibodies on the mast cell surface. Binding cross-links two IgE molecules, which causes the degranulation of the mast cell. Degranulation is the release of chemicals (red dots), including histamine, which cause the symptoms of an allergic reaction.
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