Monoclonal IgM with antibody activity for human albumin was isolated. Binding between ¹²⁵I-IgM and HSA, BSA, fragments of HSA were studied.
In contrast of rabbit anti-HSA IgG, the monoclonal IgM did not cross react with BSA. Binding between the monoclonal IgM and HSA fragments showed that the monoclonal IgM was directed to at least three antigenetic sites of HSA.
Mechanisms of recognition of antigenic sites by the monoclonal IgM and possibility of restricted heterogeneity of the monoclonal antibody were discussed.