Immunoglobulin A; Purified

Immunoglobulin A (IgA) is the second most prevalent immunoglobulin in serum, behind Immunoglobulin G (IgG). IgA is the major class of Ig in secretions and is important in local (mucosal) immunity, providing early antibacterial and antiviral defense.

Structurally, IgA exists a monomer in serum and as a dimer in secretions, such as tears, saliva, mucus, and colostrum. The IgA dimer is connected at the C terminal end of the Fc fragment by protein called a J chain. Secretory IgA is also associated with another protein, the secretory piece. The secretory piece is made in epithelial cells and is added as IgA passes into various secretions. The secretory piece helps transport IgA across mucosa and prevents it from degradation in the secretions.

Elevated levels of IgA may be found in Wiskott-Aldrich syndrome, cirrhosis of the liver, certain autoimmune disorders (e.g., rheumatoid arthritis, lupus erythematosus), and IgA myeloma, among other disorders. Low levels of IgA may be noted in hereditary ataxia telangiectasia, certain immunologic deficiency states (e.g., dysgammaglobulinemia, agammaglobulinemia), acute and chronic lymphoblastic leukemia, IgG myeloma, and more.