In Vitro Cytotoxicity of Human Lymphocytes: Reduction of the Lymphocyte Cytotoxicity Induced by Antibodies or Phytohemagglutinin by Removing Immune‐Complex‐Binding Cells

Immune‐complex‐binding cells have been excluded from suspensions of purified human lymphocytes by a rosette‐formation procedure with antibody‐sensitized ox erythrocytes. After such treatment the remaining lymphocytes were tested in a cytotoxicity assay, using 51 Cr‐labeled chicken erythrocytes as the target cells. Lymphocyte cytotoxicity for antibody‐coated target cells was profoundly reduced after removal of immune‐complex‐binding cells (more than 10 times reduction within 4 to 6 hours of incubation). Lymphocyte cytotoxicity induced by phytohemagglutinin (PHA) was also reduced by the same procedure. This reduction was less marked, the cytotoxicity of lymphocytes lacking immune‐complex‐binding cells being 26% to 82% (mean, 47%) of control lymphocytes. The results indicate that a population of immune‐complex‐binding lymphocytes is needed for lymphocyte cytotoxicity induced by target cell antibodies and also for the full expression of PHA‐induced cytotoxicity.