In an attempt to characterize the effector cells responsible for tumour resistance in Salmonella enteritidis 11RX-immunized mice the anti-macrophage agent trypan blue was used in both in vivo and in vitro experiments. Resistance was measured in vivo by the clearance of 125I from the peritoneal cavity of mice injected intraperitoneally with 125I-5-iododeoxyuridine labelled Ehrlich Ascites Tumour (EAT) cells. The in vitro correlate was measured by lysis of 51Cr-labelled tumour cells by peritoneal cells (PC) from 11RX-immunized mice. Pre-treatment of resistant mice with trypan blue greatly reduced both 125I clearance and 51Cr release. The in vitro cytolytic activity was non-specific. Fractionation of cytotoxic PC on the basis of adherence to plastic or nylon wool and buoyant density, coupled with the use of appropriate cell targets, showed that the bulk of cytotoxic activity resided with macrophages, with some contribution from other cells such as natural killer cells. Killing of labelled tumour cells could be inhibited by competition with unlabelled cells or by separating the PC and tumour cells by a cell impermeable membrane. This showed that close association between the effector and target cells was necessary before killing could occur.
Animals Carcinoma, Ehrlich Tumor