RESUMO
Two Leishmania donovani glycoconjugate ligands for the internalization receptor on BALB/c peritoneal macrophages [fucose-mannose ligand (FML) and phosphate mannogalactan ligand (PMGL)] were shown to be species-specific in a comparative phagocytosis-inhibition test. Promastigotes of L. donovani Sudan (LD1S), L. infantum, L. d. donovani, L. major (Jericho and Sudan), L. tropica, L. chagasi, L. mexicana venezuelensis, L. m. mexicana, L. m. amazonensis, L. m. pifanoi, L. m. garnhami, L. braziliensis braziliensis, L. m. amazonensis (Josefa), L. enrietti or L. adleri were incubated with macrophages in the presence of 10 micrograms/ml FML and PMGL purified from L. donovani (LD1S). Parasite internalization was determined and compared with that obtained in control experiments. Specific inhibition of phagocytosis ranged from 83% (L. donovani LD1S) to 7% (L. m. amazonensis). We could distinguish groups of Leishmania consistently with their geographic distribution and the clinical aspects of the disease. Analogous experiments with L. m. amazonensis glycoconjugates showed reciprocal results, with inhibition ranging from 76% (L. m. amazonensis) to 8% (L. donovani LD1S). L. chagasi remained separated from the Old World kala-azar agents. Possible phylogenetic implications of these observations are discussed.
Assuntos
Glicoconjugados/metabolismo , Leishmania/classificação , Macrófagos/parasitologia , Fagocitose/fisiologia , Filogenia , Animais , Células Cultivadas , Leishmania/imunologia , Ligantes , Camundongos , Especificidade da EspécieRESUMO
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.