The effect of BCG stimulation on natural cytotoxicity in the rat

The natural cytotoxic activity of lymphoid cell populations from control and BCG-stimulated rats was examined using four target cell lines, K562, CCRF/CEM, Bri8 and Mc40. In control rats, the cytotoxicity of peritoneal cells was below that of spleen cells but above that of peripheral lymph node cells. Intraperitoneal injection of BCG induced a significant dose and time-dependent augmentation of cytotoxicity by peritoneal cells from W/Not and PVG/c rats, against all four cell lines. The increased activity reached a peak on days 4 and 5 after injection and returned to control levels by day 12. Spleen and lymph node cells from stimulated rats did not show increased cytotoxicity. K562 and CCRF/CEM target cells were considerably more susceptible to killing than Bri8 and Mc40 target cells. Separation of peritoneal cells from BCG-treated rats by density-gradient centrifugation gave an interface population, enriched with mononuclear cells showing high cytotoxic activity and a pellet population enriched with polymorphs showing very low activity. Nylon-fibre column filtration gave non-adherent and adherent cytotoxic populations. Cytotoxic activity was not diminished by removing cells adhering to Sephadex G10 or cells phagocytosing carbonyl iron, suggesting that much of the activity in this system was due to non-phagocytic mononuclear cell populations.