Leishmania donovani infection enhances macrophage viability in the absence of exogenous growth factor

Bone marrow‐derived macrophages rapidly die in the absence of macrophage growth factor (M‐CSF). However, as demonstrated here, bone marrow‐derived macrophages infected with Leishmania donovani exhibit increased viability in the absence of exogenous growth factor. Forty‐eight hours after inoculation with promastigotes or amastigotes, infected cell cultures contained 180 and 95% more cells, respectively, than control cultures. This effect was specific to Leishmania infection, as uptake of latex beads or avirulent promastigotes by macrophages did not enhance cell viability. L. donovani‐infected macrophages also displayed increased phagocytic capacity, as compared with control macrophages and macrophages grown continuously in M‐CSF‐containing medium. Supernatants collected from infected cells elaborated a factor(s) that enhanced macrophage viability but did not stimulate macrophage DNA synthesis. This activity of L. donovani‐infected cell‐conditioned medium could be abrogated by preincubation of macrophages with cycloheximide before inoculation with the parasite, implying that macrophage protein synthesis is required for the elaboration of this factor(s). J. Leukoc. Biol. 55: 91–98; 1994.