Human IgA1 (Immunoglobulin A1) is a type of antibody that plays a crucial role in the immune system. It is the most abundant immunoglobulin found in mucosal secretions such as saliva, tears, and gastrointestinal fluids, where it helps to prevent infections by neutralizing pathogens and preventing their attachment to mucosal surfaces. Structurally, IgA1 consists of two heavy chains and two light chains, with a unique hinge region that makes it more susceptible to proteolytic cleavage compared to other immunoglobulins. This protein is synthesized by plasma cells and is often found in both monomeric and dimeric forms, with the dimeric form being particularly important in mucosal immunity due to its higher avidity. Abnormalities in IgA1, such as glycosylation defects, have been implicated in certain autoimmune and inflammatory diseases, including IgA nephropathy.