Leukemic lymphosarcoma (LLS) with monoclonal IgM: idiotypic specificity on the cell surface and in the cytoplasm of lymphosarcoma cells.

A case of leukemic lymphosarcoma with a small amount of monoclonal IgM in the serum is described. Immunologic investigations showed that about 10% of the abnormal cells formed EAC rosettes, that most of these cells had IgMlambda on the cell surface, and that 40% of them contained IgMlambda in the cytoplasm. Monoclonal IgM was detected in the 19S fraction of the serum despite the lack of monoclonal change as determined by serum electrophoresis or immunoelectrophoresis. The common idiotypic specificity was found in the monoclonal serum IgM, surface Ig, and cytoplasmic Ig of lymphosarcoma cells using antiidiotypic antiserum prepared against purified serum IgM. After chemotherapy, cells with idiotypic determinants disappeared and the serum IgM changed from a monoclonal to a polyclonal distribution.