Macrophage activation for tumor cytotoxicity: Tumoricidal activity by macrophages from C3H/HeJ mice requires at least two activation stimuli

Abstract

Macrophages from C3H/HeN mice treated in vivo with Mycobacterium bovis, strain BCG or in vitro with supernatants from antigen-stimulated leukocyte cultures (lymphokines) were cytotoxic to tumor cells in vitro. Macrophage tumoricidal activity, however, did not develop after identical in vivo or in vitro treatment of cells from endotoxin (LPS)-unresponsive C3H/HeJ mice. Increasing time of macrophage incubation in lymphokines, concentration of lymphokines or number of lymphokine-treated macrophages added to tumor cells did not evoke tumoricidal activity. Similarly, varying time of macrophage collection after BCG infection, numbers of BCG organisms in the infectious inoculum or numbers of macrophages from BCG-infected mice added to tumor cells also did not evoke cytotoxic activity. The tumorical defect of macrophages from C3H/HeJ mice appeared highly selective: inflammatory responses to BCG infection in C3H/HeN and C3H/HeJ mice were indistinguishable; moreover, no difference was detected between these strains in production of macrophage activation factors. Thus, despite normal inflammatory reactions, normal production of lymphokines and extensive experimental manipulation of single activation stimuli, macrophages from C3H/HeJ mice did not express tumoricidal activity in vitro. Nevertheless, macrophages from C3H/HeJ mice could develop tumoricidal activity under appropriate conditions. Macrophages from in vivo immune reactions (BCG infection, Con A injection), but not from irritant-induced peritoneal exudates, developed full cytotoxic activity after exposure to certain in vitro stimuli. These stimuli include microgram/ml concentrations of LPS and certain factors in lymphokine supernatants or supernatants from a T-cell lymphoma line. The effect of LPS but not that of lymphokines or lymphoma culture supernatants was abrogated by polymyxin B. These data suggest that the ultimate expression of macrophage cytotoxicity may depend upon certain signals from the milieu of immune reactions. These expression signals, derived from bacterial organisms or from soluble mediators of immune responses, provide the necessary and final stimulus for macrophage activation. The tumoricidal defect of macrophages from C3H/HeJ mice reflects a genetic inability of these cells to respond to environmental expression signals.