Lymphocytes Surface Membrane Immunoglobulin in Myeloma

Abstract

Abstract MOPC-315 is a BALB/c plasmacytoma that produces an IgA anti-TNP antibody (M315). 315/+ is a line derived from MOPC-315 and differentiates during in vivo growth from M315-producing, nonsecreting, lymphocytoid cells to large M315-secreting plasmacytoid cells. Studies were conducted to determine whether the small M315-bearing mononuclear cells, which account for more than one-third of the circulating mononuclear cells in mice with 315/+ tumors, were myeloma cells or host lymphocytes. Experiments conducted in CBF1 mice demonstrated that the circulating M315-bearing cells were of F1, rather than tumor, origin. Serologic and ultrastructural studies demonstrated that the cells were post-thymic T lymphocytes. After proteolytic removal, surface M315 was reexpressed in vitro by 315/+ cells, but not by T cells. M315-bearing T cells accounted for 0 to 4% of circulating mononuclear cells in mice with 315/P, a variant of MOPC-315 in which all cells synthesize M315, but only 2% of the cells are secretory. There was no obvious relationship between the frequency of M315-bearing lymphocytes and development of the humoral immunodeficiency that accompanies myeloma. These findings 1) identify an association between high levels of M315 secretion and development of M315-bearing T cells; 2) favor the view that M315 is acquired, rather than produced by host T cells; 3) raise the possibility that T cells with IgA-Fc receptors may be increased in mice with 315/+ tumors; and 4) are discussed relative to the mechanisms that have been proposed in the literature to account for the occurrence and significance of circulating, M-component-bearing lymphoid cells in murine and human myeloma.