Imunoglobulina A - IgA

Immunoglobulin A (IgA) is an antibody that plays a critical role in mucosal immunity. More IgA is produced in mucosal linings than all other types of antibody combined; between three and five grams are secreted into the intestinal lumen each day. This accumulates up to 15% of the total immunoglobulin produced in the entire body. IgA has two subclasses (IgA1 and IgA2) and can exist in a dimeric form called secretory IgA (sIgA). In its secretory form, IgA is the main immunoglobulin found in mucous secretions, including tears, saliva, colostrum and secretions from the genitourinary tract, gastrointestinal tract, prostate and respiratory epithelium. It is also found in small amounts in blood. The secretory component of sIgA protects the immunoglobulin from being degraded by proteolytic enzymes, thus sIgA can survive in the harsh gastrointestinal tract environment and provide protection against microbes that multiply in body secretions. sIgA can also inhibit inflammatory effects of other immunoglobulins. IgA is a poor activator of the complement system, and opsonises only weakly. Its heavy chains are of the type α. Pathology[edit source | editbeta]Decreased or absent IgA, termed selective IgA deficiency, can be a clinically significant immunodeficiency. Neisseria gonorrhœae (which causes gonorrhea), Streptococcus pneumoniae, and Haemophilus influenzae type B all release a protease which destroys IgA. IgA nephropathy is caused by IgA deposits in the kidneys. It is not yet known why IgA deposits occur in this chronic disease. Some theories suggest an abnormality of the immune system results in these deposits. Celiac disease involves IgA pathology due to the presence of IgA antiendomysial antibodies. Henoch–Schönlein purpura (HSP) is a systemic disorder caused by deposits of IgA and compliment component 3 (C3) in the small vessels. HSP occurs usually in small children and involves the skin and connective tissues, scrotum, joints, gastrointestinal tract and kidneys. It usually follows an upper respiratory infection and resolves within a couple weeks as the liver clears out the IgA aggregates.