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This protocol describes how to generate and harvest antibody-free L. amazonensis amastigotes, and how to infect adult Drosophila melanogaster with these parasites. This model recapitulates key aspects of the interactions between Leishmania amastigotes and animal phagocytes.
Leishmaniasis, caused by Leishmania protozoans, affects the skin, mucosa or internal organs, depending on the parasite species and immunological status of the host. Although the mouse model of infection has provided most of our understanding about this parasitic infection, it is not well suited for large-scale exploratory approaches. In our lab, we exploited the tractable and powerful genetics of the fruit fly Drosophila melanogaster to establish a model of Leishmania infection and perform a small-scale screen to identify host genes involved in the phagocytosis of these parasites (Okuda et al., 2016). In particular, a set of genes possibly linked to phagocytosis was specifically knocked-down in the fly hemocytes, using the UAS-GAL4 expression systems (Brand and Perrimon, 1993) and the survival and parasite burden of mutant-infected flies were monitored to identify factors modulating the infection.
Wild-type flies are mildly susceptible to L. amazonensis infection, with 70–80% survival over the course of a 15-day experiment, but susceptible strains might present uncontrolled parasite proliferation in the hemolymph and reduced survival (Okuda et al., 2016).
In this assay, infected flies are homogenized and a fraction of the suspension is serially diluted in Schneider’s insect medium, cultivated for 7 days and the presence of proliferating promastigotes evaluated microscopically.
This method can be used to estimate the parasite burden of flies infected with parasites expressing fluorescent proteins such as DsRed.
This protocol has been adapted from Okuda et al., 2016. Supported by the NIH (R21AI109678) to NS. The authors declare that there is no conflict of interest.