Leishmania donovani: role of microviscosity of macrophage membrane in the process of parasite attachment and internalization

Host macrophage infection by the parasite Leishmania donovani is heterogeneous, but it is not clear which factors are responsible for parasite recognition within the macrophages. One possible factor may be the alteration of the microviscosity of the macrophage membrane. This in turn may affect receptor expression and hence parasite infection. In this paper we describe alteration of the lipid composition and hence the microviscosity of the macrophage membrane in a controlled manner using liposome fusion technique. At a higher macrophage membrane microviscosity a larger number of parasites have been found to adhere to the macrophage surface. However, the proportion of parasites finally internalized when compared to parasites adhering to macrophages is inversely correlated with the artificially altered macrophage membrane microviscosity. The process of endocytosis has been examined in both native and lipid modified macrophages in the presence of several sugar antagonists. The results indicate (i) glucose and mannose are specifically involved in the binding process, and (ii) the microviscosity has a key role in controlling the macrophage parasite interaction. The results obtained so far support a model of endocytosis where expression of the receptor is a critical initial process dependent on the microviscosity of the membrane.