Quantitative studies on phytohaemagglutinin-induced cytotoxicity by human lymphocytes against homologous cells in tissue culture.

The cytotoxic effect of normal human blood lymphocytes on Chang cells in tissue culture was investigated. Cell damage was measured by release of Cr from pre-labelled tissue culture `target' cells. This method was sensitive and rendered highly reproducible results. Released Cr was not re-utilized. About 25 per cent of the Cr was spontaneously released from labelled Chang cells when incubated for 24 hours at 37°. Lymphocytes at a lymphocyte/Chang cell ratio of 25:1 led to a slight increase of this release. When phytohaemagglutinin was also present, about 50–60 per cent of the isotope appeared in the medium. Under these conditions target cells were significantly damaged within 1 hour. At a lymphocyte/Chang cell ratio of only 1:1, weak cytotoxic effects were also noted after 24 hours of incubation. The results of dose—response experiments suggested that a considerable proportion of the lymphocytes participated in the reaction. Individual variation of the cytotoxic effect of lymphocytes from different donors suggested that it could be related to the degree of histoincompatibility between lymphocytes and Chang cells. Under the present conditions contaminating erythrocytes or granulocytes did not interfere with the cytotoxic action of the lymphocytes.