The Effect of Plasmacytomas on Serum Immunoglobulin Levels of BALB/c Mice

Abstract

The effect of tumor growth on serum immunoglobulin levels and on the immune response to sheep erythrocytes (SRBC) was studied in BALB/c mice bearing MOPC-315 (IgA), MOPC-460 (IgA), MOPC-173 (IgG2a) and MOPC-104E (IgM) to gain insight into the immunologic competence of the plasmacytoma-bearing host. The initial increase of myeloma protein coincided with the first appearance of the tumor and increased as the tumor progressed. However, at the time of death there was little correlation between spleen weights, tumor size, and myeloma-protein levels. The mean serum concentration of the myeloma proteins reached a higher level in the mice bearing tumors transplanted i.p. compared to those with tumors transferred subcutaneously (s.c.). Non-myeloma immunoglobulin levels in the serum were reduced: IgM was significantly lowered in the presence of MOPC-315 injected i.p. and MOPC-460 injected s.c. and the IgG2 levels were depressed in mice injected i.p. with MOPC-315 and MOPC-104E. The only significant reduction of IgA levels was seen when MOPC-173 was transplanted i.p. The decreases observed in immunoglobulin levels correlated with plasmacytoma growth. They were specific for myeloma and were not due to tumor growth per se since the levels of all immunoglobulins tested increased in the presence of Sarcoma 37, a pleomorphic neoplasm. The primary plaque-forming cell (PFC) response of tumor-bearing animals after the injection of 0.5 ml of 10% SRBC was either similar or enhanced compared to the controls. However, with a lower SRBC dosage (0.5 ml of 2% SRBC) the indirect PFC were reduced with mice bearing MOPC-104E and MOPC-173. Tumor sizes did not seem to correlate with reduction of the PFC response. MOPC-460-bearing mice had a comparable number of PFC per spleen to those of the controls, but reduced numbers when calculated per 10 spleen cells. Consistently, hemagglutination titers were reduced in all tumor-bearing animals. The number of direct and indirect PFC per spleen was increased in mice bearing Sarcoma 37, compared to the controls. The possible implications of these findings are discussed.