The effect of tumor burden on the modulation of natural killer cell activity

In this study, experiments were conducted to investigate immuno-modulating effects of bacillus Calmette-Guerin and poly I:C as determined by the cytotoxic activity of spleen and peritoneal exudates of C3H/HeN mice against MBT-2 target cells in vitro and the tumor growth patterns in vivo. It was found that animals receiving bacillus Calmette-Guerin exhibited most of the cytotoxic activity in the peritoneal exudate cells. On the contrary, animals receiving poly I:C exhibited most of the NK activity in the splenocytes and little or none in the peritoneal exudate cells. Administration of bacillus Calmette-Guerin or poly I:C in mice bearing small tumors (1 cm. mean diameter) resulted in an increased natural killer cell activity in the exudates and splenocytes of 65 and 50 per cent respectively. No cytotoxic activity was demonstrated when either of the 2 agents was administered to mice bearing large tumors. However, surgical excision of the tumor followed by bacillus Calmette-Guerin or poly I:C administration resulted in levels of natural killer cell activity comparable to those observed in tumor-free animals or in mice bearing tumors of 1 cm. in diameter.