immunoglobulin complex IgA immunoglobulin complex A protein complex composed of two identical immunoglobulin heavy chains of the IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds, and sometimes complexed with J chain or J chain and secretory component. An IgA immunoglobulin complex may be embedded in the plasma membrane or present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. GO:0071745 Note that an IgA immunoglobulin complex has the function of antigen binding if a suitable antigen is available. protein