Clinical Significance of Immunoglobulin‐secreting Cells in the Peripheral Blood in Patients with Multiple Myeloma

Immunoglobulin-secreting cells were enumerated in the peripheral blood of 31 patients with multiple myeloma, nine patients with so-called benign monoclonal gammopathy, and ten patients with polyclonal hypergammaglobulinaemia or idiopathic hypogammaglobulinaemia. Immunoglobulin-secreting cells were detected by a haemolytic plaque assay using protein-A-coated erythrocytes in the presence of class- or type-specific rabbit anti-human immunoglobulin antisera. In about two-thirds of patients with multiple myeloma, cells secreting the same light-chain isotype of their serum M-protein increased in number, whereas this was not the case in the patients with so-called benign monoclonal gammopathy. Follow-up studies of immunoglobulin-secreting cells in multiple myeloma revealed that these cells increased or decreased, correlating with the severity of the disease, and alterations were more rapid than other clinical features. This plaque assay is therefore useful in evaluating the response to chemotherapy in patients with multiple myeloma.