LEISHMANIA-DONOVANI INFECTION ENHANCES MACROPHAGE VIABILITY IN THE ABSENCE OF EXOGENOUS GROWTH-FACTOR

Bone marrow-derived macrophages rapidly die in the absence of macropha ge growth factor (M-CSF). However, as demonstrated here, bone marrow-d erived macrophages infected with Leishmania donovani exhibit increased viability in the absence of exogenous growth factor. Forty-eight hour s after inoculation with promastigotes or amastigotes, infected cell c ultures contained 180 and 95% more cells, respectively, than control c ultures. This effect was specific to Leishmania infection, as uptake o f latex beads or avirulent promastigotes by macrophages did not enhanc e cell viability. L. donovani-infected macrophages also displayed incr eased phagocytic capacity, as compared with control macrophages and ma crophages grown continuously in M-CSF-containing medium. Supernatants collected from infected cells elaborated a factor(s) that enhanced mac rophage viability but did not stimulate macrophage DNA synthesis. This activity of L. donovani-infected cell-conditioned medium could be abr ogated by preincubation of macrophages with cycloheximide before inocu lation with the parasite, implying that macrophage protein synthesis i s required for the elaboration of this factor(s).