A protein complex composed of two identical immunoglobulin heavy chains of an IgA isotype and two identical immunoglobulin light chains, held together by disulfide bonds, sometimes complexed with J chain or J chain and secretory component, and present in the extracellular space, in mucosal areas or other tissues, or circulating in the blood or lymph. [ http://www.ncbi.nlm.nih.gov/pubmed/16362985 https://www.worldcat.org/search?q=bn%3A0781765196 ]