Test Details: Immunoglobulins play a key role in the bodys immune system. They are proteins produced by specific immune cells called plasma cells in response to bacteria, viruses and other microorganisms as well as exposures to other substances that are recognized by the body as harmful antigens. This test measures the amount of immunoglobulins A, G and M (IgA, IgG, IgM) in the blood and, in certain circumstances, in cerebrospinal fluid (CSF) or saliva. IgM antibodies are produced as a bodys first response to a new infection or to a foreign antigen, providing short-term protection. Specific IgG antibodies are produced later in the course of infection and provide long term protection. IgA provides protection against infection in mucosal areas of the body such as the respiratory tract (sinus and lungs) and the gastrointestinal tract (stomach and intestines). When passed from mother to baby during breast-feeding, it helps protect the infants gastrointestinal tract.