The
fucose-mannose ligand (
FML) of Leishmania donovani is a complex
glycoprotein fraction present in pro- and amastigotes, that interferes with parasite-macrophage interactions in vitro. In the present study, we have tested the potential immunoprotective effect of
FML on L. donovani
infection in inbred female BALB/c mice. The protection schemes included three weekly intraperitoneal administrations of
FML, supplemented or not with
saponin. Mice were challenged by
intravenous injections of 2 x 10(7) amastigotes of Leishmania donovani (LD-1S/MHOM/SD/00-strain 1S) obtained from CB hamsters' infected spleens. After 15 days of
infection, we monitored the splenocyte proliferative response to
FML in vitro by ELISA for specific antibody response, and by parasite quantification as "Leishman-Donovan Units" in liver. A significant (P < 0.001) protective effect of
FML with
saponin, but not of
FML or
saponin alone, was shown by the reduction of parasite burden in liver and by the enhancement of splenocyte proliferation. The antibody response, very low at 15 days of
infection in both untreated and control animals, showed a pronounced increase (P < 0.001) in animals sensitized with
FML/
saponin. Taken together, our results represent a 79.1 and 89.1% increase in specific proliferative and antibody responses, respectively, and an 84.4% protection in reduction of parasite liver burden. The protective potential was specifically due to
FML (P < 0.001). Under the present conditions, no toxic or nonspecific effect could be attributed to
saponin. A detailed study of the molecular events related to vaccination against murine
visceral leishmaniasis with total and fractionated
FML is currently underway.