Reversal by the MER tubercle bacillus fraction of the suppressive effects of heterologous antilymphocytic serum (ALS) on the allograft reactivity of mice

Treatment of immunized C57B1 mice with the MER fraction of BCG prevented wholly or in large part the strong immunosuppressive effects elicited by heterologous ALS against allograft reactivity, as measured by the in vitro cytotoxic activity of spleen cells against the immunizing allogeneic cells (a BALB/c plasmacytoma). Moreover, the heightened cytotoxic capacity of spleen cells bestowed by treatment of the donor with MER was manifested in some instances despite exposure to ALS. Spleen cells from MER-treated hosts were also more refractory to the direct cytotoxic action of ALS and complement in vitro.