The properties of ALP1 were studied by electrosyneresis. Migration retardation of ALP1 was observed by anti-human IgA (α-chains and secretory component) antibody or anti-human secretory component antibody after electrosyneresis on cellogel. This finding was not observed by other anti-human antibodies: IgG (γ-chains), IgA (α-chains), IgM (μ-chains), kappa light chains, and lambda light chains. Then, ALP1 was considered to contain immunoreactive secretory type of IgA (sIgA).
