Differential immunocytological expression of a paraprotein-associated idiotype is possibly related to variant immunoglobulin molecules in plasmacytoma cells.

An anti-idiotype antibody (anti-Id Ab) was made by immunization of a rabbit with the IgG-2/lambda paraprotein from a plasmacytoma patient (Sa). The antibody was directed against determinants of heavy (H) and light (L) chains on the F(ab)2 piece of the paraprotein. Using this antibody an unusual pattern of cytoplasmic fluorescence was seen with bone marrow cells of the patient. One population (type I) showed reactivity in association with gamma and lambda chains, the other (type II) with the anti-Id Ab only. So, by immunological methods, biclonality could be demonstrated using the anti-Id Ab but not with anti-isotype antibodies. L chains of mol. wt 23.5 and 17.0 kd were observed. The H and L chains of small molecular weight were not detected in the patient's serum nor in the culture supernatant. Thus, deleted and intracellularly degraded H and L chains may cause the unusual staining pattern of the type II cells.