Monoclonal antibodies to Leishmania mexicana promastigote antigens II. Cellular localization of antigens in promastigotes and infected macrophages

Abstract

In the accompanying paper by Ilg et al., it was shown that Leishmania mexicana promastigotes covalently modify a secreted acid phosphatase and other proteins by carbohydrate epitopes characteristic for lipophosphoglycan (LPG). In this study, the reaction of the anti-LPG monoclonal antibodies (mAbs AP3 and L7.25) and of mAb L3.13, an antibody directed against an epitope present on the secreted acid phosphatase but not on LPG, with promastigotes and infected peritoneal macrophages is studied by immunofluorescence and immunoelectron microscopy. AP3 labels the surface, the flagellar pocket and intracellular structures in promastigotes, while L3.13 reacts predominantly with an antigen located in the flagellar pocket. Early after infection with promastigotes, but not amastigotes, AP3 or L7.25 transiently label epitopes at the surface of live macrophages. No L3.13-reactive material is detected at the surface of infected macrophages. In permeabilized, infected macrophages, AP3 heavily labels the surface of amastigotes and the lumen of the parasitophorous vacuole, while L3.13 reveals antigen in the flagellar pocket, intracellular vesicles of amastigotes, and components in the lumen of the parasitophorous vacuole. Possible mechanistic implications for Leishmania-macrophage interaction raised by these findings are discussed.