UC Irvine

WE have reported that cell contact per se is not sufficient to explain the rapid and dramatic in vitro destruction of target L cells observed when they are treated with immune lymphocytes or non-immune phytohaemagglutinin (PHA)-stimulated lymphocytes derived from various inbred mice1. Instead, cell contact is apparently involved in the induction of additional steps, which result in the release of a soluble toxic factor(s). The presence of the factor(s) is related to the ability of the aggressor cell to promote the destruction of target L cells. Once released, the factor has a non-specific toxic effect when tested on mammalian cells of many genotypes2. Lymphocyte-induced destruction of target cells seems to be related to the capacity of the aggressor lymphocyte to undergo enlargement and form blast cells. With these observations in mind we decided to treat lymphocytes in vitro by various techniques known to induce blast cells, and to test the culture medium for the presence of cytotoxic material. © 1968 Nature Publishing Group.