Two Populations of Lymphocytes Involved in Phytohaemagglutinin‐Induced Cytotoxicity of a Dividing Target Cell

A quantitative study of the surface characteristics of cells cytotoxic against Chang cells permits the following conclusions: [1] In the presence of phytohaemagglutinin two types of cell are involved; one has Fc receptors and the other does not. Approximately two thirds of the cytotoxic activity is lost if the Fc-receptor-bearing cells are removed. [2] Both spontaneous and antibody-induced cytotoxicity is almost completely abolished by removal of Fc-receptor-bearing cells. [3] None of the cytotoxic activity, spontaneous or induced, appears to be mediated by cells that are plastic-adherent or bear surface immunoglobulin. These results are compared with similar studies by other authors.