Lipid modulation of mammary tumor cell cytolysis: direct influence of dietary fats on the effector component of cell-mediated cytotoxicity.

For understanding the mechanism by which fatty acids promote mammary tumor growth, experiments were designed to determine the influence of dietary fat concentration and saturation on both effector (Ef) and target (Ta) cells in an allogeneic antitumor cell-mediated immune response. Exposure of cytotoxic T-lymphocytes (CTL) to different fatty acids led to significant changes in the subsequent cytolytic capacity of these cells after both primary and secondary immunization. An increase in both saturated (SF) and polyunsaturated (PUF) fats led to decreased cytotoxic function after primary immunization. After a secondary challenge, the suppressive influence of SF was significantly greater than that of PUF, compared to that of the control diet containing essential fatty acids as the only fat source. This response was mediated by a direct effect on the CTL and not through an increase in suppressor or a decrease in Ef or helper cell frequency. In contrast, manipulation of the fatty acid environment of the Ta mammary tumor cells in vivo or in vitro had no significant effect on their susceptibility to lymphocyte-mediated cytotoxicity. Therefore, dietary fats may mediate their effect by a direct influence on the immunocompetent lymphocyte and not on the Ta mammary tumor cell.