What is the difference between IgG and IgA antibodies?

IgA antibodies are found in the mucosal tissue of the gastrointestinal tract, respiratory tract, and genitals and urinary tract and can be found in saliva, tears, bronchial secretions, and blood. IgA antibodies protect body surfaces that are exposed to outside foreign substances. Overall, 70% of IgA is derived from the gastrointestinal tract. If IgA antibodies are elevated to a particular protein (antigen), this can indicate an immune response to mucosal irritation or damage. In contrast, IgG antibodies are produced by plasma B cells and are found in all body fluids. About 75-80% of the immunoglobulins in the blood are IgG. These two antibodies also have considerably different half-lives. IgA antibodies have a half-life of 6-8 days so elevated IgA antibodies indicate recent exposure. In contrast, the half-life of IgG is longer, approximately 23 days, but varies according to IgG1, IgG2, IgG3, and IgG4 subclasses, and can indicate a prolonged exposure or sensitivity.