Production and characterization of antibodies specific for domains of human IgM

A method of preparing antibodies against c mu 3 and c mu 4 domains of human IgM is described. c mu 3- and c mu 4-binding antibody fractions were isolated by affinity chromatography from IgG fractions of antisera raised against Fc5 mu and Fc mu' fragments. c mu 3 and c mu 4 fragments had been prepared from human IgM kappa (Key) by hot trypsin digestion. Haemagglutination inhibition tests showed that the c mu 4-binding fraction only reacted with c mu 4 fragments. The c mu 3-binding fraction reacted with c mu 3 fragments but showed a minor reaction with c mu 4 fragments. Immunization with Fc mu' fragments predominantly yielded antibodies against the c mu 3 domain, whereas immunization with Fc5 mu fragments yielded antibodies more directed against the c mu 4 domain. Immunization with isolated c mu 4 fragments led to the production of antibodies which reacted with the isolated c mu 4 domain but not with the c mu 4 domain within the larger structures of Fc mu' or Fc5 mu fragments.