Leishmania amazonensis Engages CD36 to Drive Parasitophorous Vacuole Maturation

Abstract

Leishmania amastigotes manipulate the activity of macrophages to favor their own success. However, very little is known about the role of innate recognition and signaling triggered by amastigotes in this host-parasite interaction. In this work we developed a new infection model in adult Drosophila to take advantage of its superior genetic resources to identify novel host factors limiting Leishmania amazonensis infection. The model is based on the capacity of macrophage-like cells, plasmatocytes, to phagocytose and control the proliferation of parasites injected into adult flies. Using this model, we screened a collection of RNAi-expressing flies for anti- Leishmania defense factors. Notably, we found three CD36-like scavenger receptors that were important for defending against Leishmania infection. Mechanistic studies in mouse macrophages showed that CD36 accumulates specifically at sites where the parasite contacts the parasitophorous vacuole membrane. Furthermore, CD36-deficient macrophages were defective in the formation of the large parasitophorous vacuole typical of L. amazonensis infection, a phenotype caused by inefficient fusion with late endosomes and/or lysosomes. These data identify an unprecedented role for CD36 in the biogenesis of the parasitophorous vacuole and further highlight the utility of Drosophila as a model system for dissecting innate immune responses to infection.

Author Summary

Leishmaniasis is caused by Leishmania parasites and transmitted to humans by sandflies. After the establishment of infection, the intracellular parasite form, known as an amastigote, preferentially infects and replicates in macrophages, cells otherwise specialized for killing microbes. To overcome macrophage lethality, Leishmania possesses a sophisticated evasion strategy that sabotages macrophage defenses. The cell biology of Leishmania-macrophage interactions is not completely understood, because of the complexity of the host-parasite relationship and limited technical resources available in the classical mouse infection model. In this study we created a model of leishmaniasis in fruit flies, which have advantages of genetic tractability, low cost, and high conservation. By screening a collection of genetically modified flies, CD36-like receptors were identified as factors involved in the Leishmania-phagocyte interaction. Further testing in CD36-deficient mouse macrophages showed that they did not support parasite proliferation due to the inability of parasites to enlarge the parasitophorous vacuole, a strategy used to avoid toxicity of reactive nitrogen species. The participation of CD36 in the control of the parasitophorous vacuole, which is an altered phagosome, has further implications for diseases such as Alzheimer’s disease, atherosclerosis, and certain bacterial infections where CD36 is a known phagocytic receptor.