Fine structure and cytochemistry of the interaction between Leishmania mexicana amazonensis and rat neutrophils and eosinophils.

The fine structure of the in vivo and in vitro interaction process between promastigote and amastigote forms of Leishmania mexicana amazonensis with rat peritoneal neutrophils and eosinophils was studied. For in vivo experiments the parasites were inoculated into the peritoneal cavity and samples were collected after different times. Both neutrophils and eosinophils readily ingested and digested the parasites within endocytic vacuoles. Attachment of the parasites to the eosinophils induced their degranulation with the release of granule contents onto parasite surface causing its destruction. Ingestion of parasites by eosinophils, but not by neutrophils, induced drastic morphological changes finally leading to leucocyte lysis with liberation of intact granules. This fact may increase the extracellular parasite killing. For in vitro interactions, peritoneal exudate cells were collected by washing. Normal rat autologous serum was shown to be required for both attachment and ingestion of the parasites by the granulocytes. Results were similar to those obtained from in vivo experiments. Parasites incubated with serum presented a thicker coat that appears to mediate their attachment and subsequent ingestion by leucocytes. The cytochemical localization of acid phosphatase and peroxidase showed that leucocyte granules fused with the parasite-containing endocytic vacuoles. Images were obtained suggesting that the binding of the parasites to eosinophil surface triggers an exocytic process with releasing of the granule content onto the parasite surface.