Immunoglobulin isotypes on monoclonal blood lymphocytes in human plasma cell myeloma.

Purified blood lymphocytes from 30 patients with myelomatosis were studied. B lymphocytes with sIg were identified by direct IFL after staining with F(ab')2-fragments of antibodies against heavy or light chain specificities. Forty per cent of the patients had B lymphocyte values above the normal range; the median percentage of B cells was 7.25 as compared to 4.5 for control donors (p less tha 0.01). Lymphocytes bearing the light chain isotype of the myeloma protein were selectively increased in 20 of 30 patients suggesting monoclonality. The heavy chain specificities on such lymphocytes were usually that of the serum myeloma globulin sometimes together with mu and/or delta. Tentatively, mu and/or delta carrying monoclonal lymphocytes may represent early precursors to the malignant plasma cells. In patients with IgG myelomas, gamma-bearing blood lymphocytes may be late during maturation. The presence of monoclonal lymphocytes with surface bound gamma chains in untreated patients was associated with unfavourable prognosis.