Alloinduced suppression and cytotoxicity: two functions of a single cell

Using different experimental approaches we here show that the suppression and cytotoxicity generated during a one-way mixed lymphocyte culture (MLC) are mediated by a single cell population, in this case the cytotoxic T lymphocyte (CTL). Results of limiting-dilution analysis of cells from a 4-day MLC demonstrate the coexpression of both functions and argue against the existence of a separate suppressor cell population that regulates the in vitro alloresponse. The suppressive quality of CTL is also exemplified in cells with a clonal origin, such as cloned cytotoxic T lymphocytes and the mouse X rat hybridoma PC60. Further experiments demonstrate that this suppression is not primarily mediated through lysis of the stimulator cells, and studies in the PC60 model suggest that lysis and suppression may have different induction requirements.