Immunoglobulin secretion by peripheral blood and bone marrow B cells in patients with multiple myeloma. Studies by the reverse haemolytic plaque assay.

The reverse haemolytic plaque assay (RHPA) was used to enumerate circulating and bone marrow (BM) immunoglobulin secreting cells (ISC) in patients with multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS), as well as in normal controls. Significantly greater quantities of plaque forming cells (PFC) secreting the same isotype of the serum M component were detected in the peripheral blood of MM patients than in the blood of MGUS patients or normal subjects. Comparative analysis of the numbers of monoclonal PFC in both peripheral blood (PB) and BM at diagnosis usually showed a higher number as well as more precocious chemotherapy-induced variations of ISC in the BM compartment than in the PB. Although large individual variations were observed during follow-up studies of MM patients, persistently increased or decreased levels of monoclonal PFC were often found to accompany (and sometimes to precede by months) the phases of relapse or remission, respectively. Similarly to IgG-MGUS patients, a distorted ratio of IgG kappa to IgG lambda secreting cells was consistently detected in patients with smouldering MM, although the total number (IgG kappa plus IgG lambda) of ISC appeared within normal limits. It is suggested that, in addition to other clinical and laboratory criteria, the RHPA may be of value in the diagnosis and follow-up of patients with monoclonal gammopathies.