T-cell-independent activation of macrophages by viable BCG in tumor-bearing mice

Abstract The effect of viable or killed BCG on the depressed bactericidal activity of macrophages in mice bearing transplantable sarcoma-180, and the relationship between macrophage activation by BCG and delayed hypersensitivity to PPD were studied. Inoculation of the tumor into outbred ddN mice markedly depressed the bactericidal activity of macrophages against Listeria monocytogenes . Pretreatment with viable BCG enhanced bactericidal activity markedly. Pretreatment with killed BCG moderately increased bactericidal activity, which was detected within a few days after treatment. Pretreatment with either viable or killed BCG induced inhibition of in vitro macrophage migration 14 days after treatment and induced a positive in vitro blastogenic response. Moreover, striking activation of macrophages was obtained in nude mice 14 days after treatment with viable BCG, although migration inhibition was not detected. These results suggest the presence of a macrophage activation mechanism independent of sensitized T lymphocytes.