Rat natural killer cell and cytotoxic T cell lysis of H‐2‐negative murine embryonal carcinoma cells

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Abstract
H‐2‐lacking murine embryonal carcinoma (EC) cells have been proposed as universal targets for natural killer (NK) effectors from different species because their killing appeared to be uncomplicated by potential T cell effector mechanisms (Stern, P. L. et al., Int. J. Cancer1981. 27: 679). While some previous studies had shown that murine cytotoxic T cells were unable to lyse EC cells, rat T killers are shown here to be active against these targets and to be distinguishable from NK cells.Percoll density fractionation of rat peripheral blood lymphocytes enriches in parallel for NK‐mediated lysis of both EC or YAC target cells. These NK cells, unlike T cells, do not mediate lectin‐dependent and cell‐mediated cytotoxicity (LDCC) of NK‐insen‐ sitive target cells. This procedure is thought to reveal the total cytolytic potential of stimulated T cell populations, regardless of specificity. In contrast to previous results with mice, we found that allogeneically primed rat cytotoxic T cells can kill murine EC cells in LDCC and, further, that rat cytotoxic T cells, generated by stimulation with mouse spleen cells in vitro, can lyse murine EC cells directly.This demonstration of T cell lysis of EC cells suggests that either there is a novel mechanism of lysis operating without requirement for major histocompatibility com‐ plex (MHC) structures, or EC cells express some hitherto unidentified MHC‐like structures on their cell surface.