PROTECTIVE EFFECT OF NEOGLYCOPROTEIN-CONJUGATED MURAMYL DIPEPTIDE AGAINST LEISHMANIA-DONOVANI INFECTION - THE ROLE OF CYTOKINES

Active targeting of muramyl dipeptide (MDP) to macrophages was studied by conjugation with the neoglycoprotein, mannosyl human serum albumin (mannose-HSA) using visceral leishmaniasis as the model macrophage di sease. Conjugation did not decrease the affinity of the neoglycoprotei n for macrophage mannose receptor, Mannose-HSA-MDP was 50 times more e fficient than free MDP in inhibiting the growth of Leishmania donovani inside peritoneal macrophages. Moreover, in a 60-day murine model of visceral leishmaniasis, 95% of the spleen parasite burden was reduced by mannose-HSA-MDP at a dose of 0.5 mg/kg/day given for 4 days. Free M DP at a similar dose had very little effect. In vitro exposure of MDP caused enhanced generation of O-2(-) by macrophages, whereas generatio n of nitric oxide (NO) was not induced. The elevated antileishmanial a ctivity of MDP-treated macrophages in culture was abrogated by O-2(-) scavengers. In contrast, considerably enhanced amounts of NO and O-2(- ) were generated from macrophages of mannose-HSA-MDP-treated animals, and their splenocytes secreted soluble factors providing all the signa ls required for the induction of NO biosynthesis. The increase in NO p roduction was paralleled by a concomitant increase in antileishmanial activity, which was reversed by NO synthesis inhibitors. Splenocyte su pernatants treated with anti-IFN-gamma or anti-TNF-alpha Abs suppresse d inducible NO generation by macrophages. Moreover, i.v. administratio n of anti-IFN-gamma and anti-TNF-alpha along with mannose-HSA-MDP grea tly reduced protection against L. donovani infection. Neoglycoprotein- conjugated MDP, therefore, activated mouse macrophages in vivo to kill L. donovani, and this may depend on the physiologic generation of NO induced by IFN-gamma and TNF-alpha.