Quantitative immunochemical determination of human secretory IgA

Secretory IgA from human colostrum was fragmented by mercaptoethanol. The heavy chain fraction was prepared by means of gel chromatography on Sephadex G 100 in 1 N acetic acid. After immunization of rabbits with this heavy chain fraction the resulting antiserum contained antibodies specific for the alpha-chain and antibodies against the secretory component. These antibodies were separated by means of immunosorption. The antibodies against the secretory component precipitate free secretory component as well as bound secretory component. The antiserum is suitable for quantitative determination of secretory IgA, but free secretory component reacts too. Also secretory IgM may react, because secretory IgM contains up to 70% secretory component.