Immunoglobulin production by lymphocyte hybridomas

We have investigated immunoglobulin production by cloned hybrid cells. gamma2b heavy chains, but not gamma1 or gamma21, exist in two forms, differing in molecular weight, galactose labeling and charge. Hybrid molecules containing gamma2b and gamma1 heavy chains were secreted by hybridoma cells synthesizing Ig molecules of both subclasses. However, cells synthesizing both IgM and IgG chains did not secrete mu-gamma hybrid molecules. We have surveyed many new hybridomas derived from different mouse strains: 10% of those secreting IgM produce a mu chain which is about 5000 daltons larger than normal mu. Two IgM-secreting lines were studied in detail and were found to bear mu but not delta in their membrane. Intra- and extracellular mu differ in molecular size; pentameric IgM-containing molecules of both sizes were observed in the membrane fraction.