Immunoglobulin A (IgA), animation. IgA is produced by plasma cells (top left), a type of B lymphocyte white blood cell. It is a Y-shaped molecule, that is often secreted as a dimer (two molecules joined together, red). IgA is the most abundant immunoglobulin in mucosal linings, including those of the intestine. After it is secreted, IgA attaches to a polymeric immunoglobulin receptor (blue) on the surface of a mucosal tissue epithelial cell (brown cube) and is transported into the cell via endocytosis. The receptor-IgA complex travels through the cell before being secreted through the luminal surface of the epithelial cell. In the lumen it binds to the mucous layer where it protects against pathogens. Part of the receptor remains attached to the IgA. This is known as the secretory component and protects IgA from being degraded by enzymes.
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