Alteration of Leishmania donovani infection levels by selective impairment of macrophage signal transduction.

Leishmania donovani is an obligate intracellular protozoan which residues and multiples in macrophages. The molecular basis for this host-parasite interaction is poorly understood. Targeting a signal transduction pathway in the macrophage would allow this parasite to manipulate cellular gene expression, and this may aid in ensuring its survival. We demonstrate that in macrophages infected with L. donovani for 18 h, c-fos gene expression mediated through protein kinase A was unaffected under conditions where there was an impairment of protein kinase C (PKC)-mediated c-fos gene expression. This selective impairment of PKC-mediated c-fos gene expression was substantially augmented in macrophages put in contact with L. donovani promastigotes or amastigotes for only 1 h. Treatment of macrophages with L. donovani-conditioned media was not sufficient to significantly impair signal transduction. These data revealed that L. donovani selectively impaired the transmission of information from the cell surface to the nucleus and that this effect is induced very soon after macrophage-parasite contact. The biologic significance of this altered signal transduction in the macrophage with respect to infection with L. donovani was then examined by treating macrophages with various protein kinase inhibitors prior to infection with amastigotes. Macrophages that were treated with PKC inhibitors demonstrated an increase in the initial uptake of the parasite and carried heavier infection levels than did controls. In contrast, treatment of macrophages with an inhibitor of calmodulin-dependent protein kinase (CaM-PK) did not show significant differences in the initial uptake of parasite, but prolonged impairment of CaM-PK resulted in a decrease in the level of macrophage infection. Further experiments revealed that promastigote proliferation was severely impaired by the CaM-PK inhibitor but not any of the other inhibitors.