Leishmania enriettii amastigotes: demonstration of fibrillar surface.

An extensive fibrillar surface was identified in situ by transmission electron microscopy on the amastigote stage of the macrophage intracellular parasite, Leishmania enriettii. Attachment to the amastigote surface of 20-160-nm fibrils was clearly evident on organisms that had been isolated from guinea pigs. Surface fibrils were not detected after in vitro transformation of the amastigote to the promastigote. Incubation of amastigotes in heat-inactivated guinea pig serum containing a high titer of antibodies to L. enriettii followed by exposure to ferritin-conjugated antibody to guinea pig IgG resulted in labeling of surface fibrils, a result indicating that these fibrils are of parasite origin. Shedding of labeled fibrils was also evident.