Kinetic analysis of ex vivo human blood infection by Leishmania.
Abstract
The leishmanioses, vector-borne diseases caused by the trypanosomatid protozoan Leishmania, are transmitted to susceptible mammals by infected phlebotomine sand flies that inoculate promastigotes into hemorrhagic pools created in host skin. We assumed that promastigotes are delivered to a blood pool, and analyzed early promastigote interactions (0-5 min) with host components, which lead to parasite endocytosis by blood leukocytes, and to host infection. Promastigotes were incubated with NHS or with heparinized blood in near-physiological conditions, and we used cell radioimmunoassay and flow cytometry to measure the on-rate constants (k(+1)) of promastigote interactions with natural opsonins and erythrocytes. We obtained quantitative data for parasitized cells to determine the time-course of promastigote binding and internalization by blood leukocytes. In these reactions, promastigotes bind natural opsonins, immune adhere to erythrocytes and activate complement cytolysis, which kills approximately 95% of promastigotes by 2 min post-infection. C3-promastigote binding is a key step in opsonization; nascent C3-promastigotes are the substrate for two simultaneous reactions, C3-promastigote immune adherence (IA) to erythrocytes and ...Continue Reading
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