J‐chain determinants in polymeric immunoglobulins

An antiserum was raised against purified J‐chain from S‐sulfonated human secretory IgA and was tested for its reactivity with secretory IgA, polymeric myeloma proteins of IgA 1 and IgA 2 subclasses and a Waldenström IgM macroglobulin. The antiserum, which was absorbed with normal human IgG and L‐chains, developed a single precipitin line with the following S‐sulfonated proteins: purified J‐chain, secretory IgA, polymeric IgA 1 , and IgA 2 , and IgM. The antiserum also reacted with the same proteins after complete reduction and alkylation. The antiserum did not precipitate the same polymeric immunoglobulins in their native states. At high concentrations, however, native polymeric serum IgA and IgM inhibited the precipitin reaction between the purified J‐chain and its antibodies. In contrast, native secretory IgA displayed no inhibition in this system. After treatment of these immunoglobulins with 8 M urea, 5 M guanidine, or 1 M propionic acid, the J‐chain determinants became accessible and were precipitated with the anti‐J‐chain antiserum, with the exception of IgM which displayed very weak reactivity only after exposure to 5 M guanidine. In conclusion, J‐chain determinants are accessible only to a very limited extent in native serum polymeric IgA and IgM, and none are detectable in the native secretory IgA. Most of the determinants become easily available by mere denaturation of these immunoglobulins with exposure to several kinds of dissociating agents.