Rat NK cells active against lymphoma and sarcoma tumor cells are probably identical

Rat NK cells, which lyse Mc7 sarcoma cells in a 6-hr chromium-release assay (CRA), have been shown previously to lack the characteristics of mature T cells, B cells, and macrophages, and to have low affinity Fc receptors but no C3 receptors. In these respects they are identical to those rat NK cells active against lymphoma cells. In this study we examined whether the rat NK cell-mediated lysis of sarcoma target cells and lymphoma target cells could be distinguished by additional methods, including those that have been claimed to distinguish these two effector systems in the mouse. Lysis of both types of target cell was studied in parallel by using a 4 to 6-hr CRA. The results showed that the two types of killer cells had similar age distribution and adherence to nylon wool, and preincubation in vitro caused augmentation of both activities. Normal spleen cells and BCG-activated peritoneal exudate cells (PEC) had equal proportions of anti-lymphoma and anti-sarcoma tumor NK activities, but evidence of a distinct subpopulation of anti-EL4 NK cells in activated PEC was found. Both killer cell types fractionated in the same manner on Percoll density gradients and were sensitive to anti-asialo GM1 serum and complement. Studies with the W3/13, W3/25, and OX8 monoclonal antibodies showed that rat NK cells were heterogeneous, but anti-sarcoma and anti-lymphoma killer cells had identical surface markers. Although lysis of some target cells occurred only after a pronounced lag period, this phenomenon was observed with both sarcoma and lymphoma targets. Sarcoma and lymphoma targets cross-competed in cold target competition assays. These results taken as a whole strongly suggest that in the rat, those NK cells that kill sarcoma cells and those that kill lymphoma cells, are identical.