Cytotoxicity of human lymphocytes induced by pokeweed mitogen or in mixed lymphocyte culture. Specificity and nature of effector cells

Induction of natural killer cell activity and allocytotoxicity in human peripheral blood lymphocytes after mixed lymphocyte culture

The K-562 tumour cell is a highly susceptible target for natural killer (NK) cell lysis by lymphocytes of human peripheral blood. We have studied the antigenic relationship between the recognition sites for lysis of lymphoid and various tumour target cells by cytolytic T lymphocytes (CTL) and NK cells induced in mixed lymphocyte cultures (MLC). The characteristics of these two effector cell types have also been investigated. It was demonstrated that fresh NK cells lose their NK lytic activity when cultured alone. Cell lines not susceptible to lysis by fresh NK cells are lysed by MLC-induced NK cells. There is no antigenic relationship between the recognition sites for the alloreactive T lymphocytes and MLC-generated NK cells expressed on the lymphoid target cells and the tumour target cells, respectively. The MLC-generated alloreactive T cells and NK cells are not identical. The MLC-generated NK cells are different from the fresh NK cells present in the peripheral blood.

"NK-like" cytotoxicity of human lymphocytes cultured in media containing fetal bovine serum

Human peripheral blood lymphocytes (PBL) were found to be highly cytotoxic to a human malignant melanoma target cell line after the PBL were cultured in medium supplemented with 20% fetal bovine serum (FBS). The effector cells had surface markers similar to those of non-cultured NK effectors against melanoma targets. Both NK (without culture) and the culture-induced cytotoxic effectors had Fc gamma receptors, lacked Fc mu receptors and were either heterogeneous for E receptors or had low-affinity E receptors. Cells required to generate the FBS response were sensitive to anti-T serum plus complement, passed through a nylon-fiber column, formed E rosettes, but lacked detectable receptors for the Fc portions of either IgG or IgM. These results suggest that events causing activation of T cells such as culture of PBL in FBS-containing medium, result in the augmentation of NK activity.

Interaction of choriocarcinoma cells and human peripheral blood lymphocytes. Resistance of cultured choriocarcinoma cells to cell-mediated cytotoxicity by mitogen-activated lymphocytes

Cultured choriocarcinoma (Be Wo) cells exist that share many of the morphologic and bio-synthetic properties of normal human trophoblasts. In an attempt to develop a model for the immunologic relationship between a sensitized mother and fetus, we mixed Be Wo cells with mitogen-activated cytotoxic lymphocytes in vitro. Be Wo cells were resistant to the cytolytic effects of the activated lymphocytes despite 24-h exposure and intimate cell-to-cell contact as determined by microscopy. Control target cells, a line of human hepatoma cells, were readily destroyed. Cytotoxicity was measured by determining residual radioactivity of [(3)H]thymidine-labeled target cells after exposure to activated lymphocytes. Employing the quantitative assay, we confirmed the morphologic results and showed that Be Wo and a number of other choriocarcinoma cell lines were resistant to the cytotoxic effects of lymphocytes activated by phytohemagglutinin, pokeweed mitogen, and allogeneic cells in mixed lymphocyte cultures. Moreover, Be Wo cells were resistant to injury over a wide range of killer to target cell ratios. Significant killing of the Be Wo cells occurred only after prolonged exposure (48 and 72 h) to the activated lymphocytes. We suggest that one mechanism that may assist the fetus (or a choriocarcinoma) in its immunologic survival is the intrinsic resistance of trophoblast cells to lymphocyte-mediated cytotoxicity.