Selective blocking of T cell-mediated in vitro cytotoxicity to a xenogeneic tumour by anti-immunoglobulin sera.

Rejection of a xenograft by BALB/c mice results in a highly potent immune peritoneal population. When these immune cells are analysed by using two in vitro assays in parallel, at least two active cytotoxic mechanisms can be demonstrated. Target cells can be labelled with [125I]iododeoxyuridine (IUdR) before the effector cells are added and the detachment of the DNA from plastic can be used to detect cell-mediated immunity. This is referred to as the direct cytotoxicity test. This assay is largely dependent on T-cell function and evidence is presented here that it can be inhibited by anti-immunoglobulin (anti-Ig) antisera. The second test, which reflects the inhibition of incorporation of IUdR by previously mixed effector and target cells, is called the cytostatic assay. This test, although presumably affected by cytotoxic T cells, also reflects a T-independent mechanism which is not inhibited by anti-Ig sera.