Studies on the origin of the precursor cells in multiple myeloma, Waldenström's macroglobulinaemia and benign monoclonal gammopathy. I. Cytoplasmic isotype and idiotype distribution in peripheral blood and bone marrow.

Lymphocytes and plasma cells in the peripheral blood and bone marrow of patients with multiple myeloma, benign monoclonal gammopathy and Waldenström's macroglobulinaemia were investigated for their cytoplasmic immunoglobulin distribution. Anti-idiotypic sera were used as markers for monoclonality. Double-wavelength fluorescence microscopy made it possible simultaneously to use anti-isotype and anti-idiotype sera with different fluorochromes. It was concluded that, in the bone marrow, the monoclonal event starts at the level of a lymphoid cell which has already been committed to its final isotype. The size of the monoclonal expansion in the bone marrow and the cell types involved in the proliferation may determine whether spread occurs. Polyclonal lymphoid cells containing cytoplasmic immunoglobulins were decreased in the peripheral blood and exhibited a reversed kappa/lambda ratio when compared to the immunoglobulin-containing cells in the bone marrow. This finding suggests a light chain-type related depression of polyclonal B cell precursors.