Interferon-induced augmentation of cytotoxic killer cell generation in mixed lymphocyte cultures: analysis of the effector cell product.

Alloreactive cytotoxic lymphocytes were generated during mixed lymphocyte cultures (MLC). Human leucocyte interferon added during MLC gave rise to a moderate inhibition of thymidine uptake, yet augmentation of the allospecific cytotoxic product generated was found. Effector cell activities after MLC in the presence and absence of interferon against autologous cells were negligible, whereas NK-sensitive targets and antibody-coated target cells were killed to a higher extent, comparably, by cells generated during MLC in the absence of interferon. Cell separation experiments and cold target inhibition experiments were performed and showed that the effector cells generated with and without interferon had similar characteristics and were distributed among the same lymphocyte subpopulations. The key conclusion was that the augmented cytotoxicity was caused by alloreactive T cells, most of which were F(c) gamma receptor-negative, and was not due to enhanced 'NK-like' or antibody-dependent cell-mediated cytotoxic activity induced by interferon.