Macrophages induce antibody-dependent cytostasis but not lysis in guinea pig leukaemic cells

Guinea pig and mouse peritoneal macrophages formed antibody-dependent rosettes with guinea pig L2C leukaemic cells, but were unable either to phagocytose the cells or to kill them extracellularly as judged by the retention of 51Cr. Macrophages previously activated by BCG in vivo also failed to exhibit phagocytosis or cytoxicity towards the antibody-coated cells. These failures could not be attributed to deficient function of the macrophages nor to antigenic modulation of the L2C cells. The antibodies involved were capable of mediating lysis by complement, and ADCC by human leukocytes. However macrophages were cytostatic to antibody-coated L2C cells in that uptake of 3H-thymidine or 3H-deoxycytidine was abruptly and in some cases completely inhibited upon cell contact being established. Antigenic modulation which had proceeded sufficiently to protect against lysis by complement did not protect against cytostasis. Syngeneic macrophages had greater cytostatic activity than did allogeneic or xenogeneic. Macrophage activation by BCG did not result in significantly increased cytostasis. A univalent antibody derivative Fab/c was also capable of mediating cytostatis by the macrophages.