In vitro sensitization of human lymphocytes against histiocytic lymphoma cell lines. II. Characterization of two different effector activities and of suppressor cells.

Peripheral blood lymphocytes (PBL) from normal human donors were tested for natural killing (NK) activity and for two types of in vitro induced cytotoxicity against allogeneic diffuse histiocytic lymphoma (DHL) cell lines. Culture-induced cytotoxic (CIC) activity developed in cultures of unseparated PBL incubated in the presence of fetal bovine serum (FBS) but not in the presence of human serum (HS). The CIC mediating effector cells were removed by nylon wool adherence, whereas the NK cells were not. A second type of in vitro induced cytotoxicity was obtained by specific sensitization against DHL cells (SIC). The SIC effector cells were not retained by nylon wool. SIC was manifested after sensitization in medium containing HS but not in FBS-containing medium unless nylon wool adherent cells were removed before sensitization. The lack of SIC in the presence of FBS appeared to be due to nylon wool-adherent suppressor cells. Such suppressor activity was also removed by plastic adherence or elimination of phagocytic cells. CIC and suppressive activity were found to be mediated by different cell populations.