Immune responses to weakly immunogenic murine-leukemia-virus-induced tumors. VIII. Characterization of suppressor cells

YAC is a Moloney-virus-induced tumor of A mice. YAC-injected A and C57BL/6 mice generated suppressor cells. The suppressive function of the cells was tested by determining the ability of splenocytes from YAC-injected mice to inhibit the in vitro cytotoxic responses of primed splenocytes. It was found that suppressor cells passed through a nylon-wool column did not adhere to the plastic surface and resisted treatment with rabbit antimouse brain serum and guinea-pig complement. Therefore, the suppressor cells were defined operationally as 'null' cells. The suppressor cells did not demonstrate high efficiency; a relatively high concentration of suppressor cells was required to achieve an effective inhibiting action. These findings are discussed in terms of the heterogeneity of suppressor cells.