RESUMO
Leishmania donovani, the agent of human visceral leishmaniasis, is an intracellular parasite that must be recognized and internalized by host macrophages to complete its biological cycle. In a search for possible ligands for macrophage surface receptors, glycoconjugates were obtained from Leishmania promastigotes by aqueous, phenol-aqueous, and alkaline extraction. A fucose-mannose glycoproteic ligand, a lipopeptidephosphoglycan, and a phosphate mannogalactan ligand were purified from promastigotes and analyzed for their chemical contents, with special attention to their glycidic moieties. Sugars that were identified as components of these glycoconjugates were tested for their capacity to inhibit promastigote internalization by BALB/c peritoneal macrophages in vitro. Neutral hexoses showed little inhibitory activity; fucose, charged monosaccharides, and a mannose polymer showed the highest activity. Two of the glycoconjugates (fucose-mannose glycoproteic ligand and phosphate mannogalactan ligand) purified from promastigotes were potent inhibitors of internalization, 75% inhibition being obtained at concentrations of 6 to 10 micrograms/ml. The simultaneous presence of both ligands in low concentrations yielded an increase in inhibitory activity above that found for each ligand alone, indicating that promastigotes may use at least two receptor sites for penetration into macrophages. These ligands are specific inhibitors of L. donovani promastigote phagocytosis, since 10 micrograms of each ligand per ml interfered neither with internalization of yeast cells nor with phagocytosis of Leishmania adleri promastigotes.
Assuntos
Glicoconjugados/farmacologia , Leishmania donovani/imunologia , Macrófagos/parasitologia , Fagocitose/efeitos dos fármacos , Animais , Técnicas In Vitro , Leishmania donovani/análise , Ligantes , Macrófagos/fisiologia , Camundongos , Peso Molecular , Monossacarídeos/farmacologia , Polissacarídeos/farmacologia , Receptores de Superfície Celular/fisiologiaRESUMO
An enzyme-linked lectin assay (ELLA) based on the ELISA assay, using intact formalin-fixed promastigotes to coat poly-L-lysine-treated microtiter plates is described. The assay was used to study the lectin receptors of Leishmania donovani chagasi, L. donovani donovani and L. mexicana amazonensis. ConA, RCA, WGA, and PNA receptors were found in the three parasites. SBA receptors were found to be as frequent as the other receptors in L. donovani chagasi but not in the other two parasites which showed little SBA binding. Trypsin treatment of the two L. donovani subspecies did not remove any of the lectin receptors studied.