Identification and separation by bacterial adherence of human lymphocytes that suppress natural cytotoxicity

Human lymphocyte subpopulations (B1, B2T1, T2T3, and T4, our denomination) have been previously identified by bacterial adherence, and differences in functions (mitogen responses, specific cytotoxicity, and natural killing activity) have been associated with some of these subpopulations. The natural killing activity (NK) was located in the T4 lymphocyte subpopulation. Here we investigated the possibility that lymphocytes capable of suppressing the NK activity of the T4 cells could be identified and isolated from one of the other lymphocyte subpopulations. Freshly isolated, monocyte-depleted human peripheral blood lymphocyte (PBL) were separated into adherent and nonadherent cells after centrifugation against various bacterial monolayers. The PBL and the resulting subpopulations of PBL were tested as effector cells in a 4-hr cytotoxicity assay against the CEM lymphoblastoid cell line. The addition of viable T2 lymphocytes to either PBL or T4 lymphocytes resulted in a significant decrease in NK activity, whereas no decrease was seen when T1, T1T3, or killed T1T2 cells were added. This decrease in NK activity was not due to a simple dilution of the active NK cells, to alteration of the lymphocytes by their processing on the bacterial monolayers, or to a competition for binding to the target cells. We concluded that the T2 lymphocyte subpopulation contains the cells capable of suppressing the ability of normal human peripheral blood lymphocytes (T4 subpopulation) to perform natural killing.