In primary human monocyte-derived macrophages exposed to Human immunodeficiency virus type 1, does the increased intracellular growth of Leishmania infantum rely on its enhanced uptake?

Concurrent uncontrolled development of human immunodeficiency virus type 1 (HIV-1) and Leishmania spp. is regarded as an emerging pathogenic combination in countries where human beings are exposed to these two micro-organisms. The present study was aimed at exploring whether HIV-1 development within a culture of human monocyte-derived macrophages (MDMs) affected the further development of luciferase-encoding Leishmania infantum using the luciferase activity as a readout assay. It was demonstrated that, in cultures of HIV-1-loaded MDMs exposed to axenic amastigotes, the luciferase activity was higher than in HIV-1-free MDMs. As a preliminary approach to deciphering the possible mechanism through which HIV-1 can affect Leishmania infantum, attention was focused on the very early processes that could underlie this increased luciferase activity. Using GFP-labelled parasites, it was possible to establish that, in HIV-1-infected MDMs, the percentage of GFP-expressing MDMs was higher (10-20 %) than in cell cultures not exposed to HIV-1 (5 %). Two-colour immunofluorescence staining suggested that HIV-1 indirectly affects the uptake of parasites inside MDMs. Thus, the observed phenomenon seems to be linked with a higher uptake of parasites within MDMs. Taken together, the data reported here may contribute to our understanding of disseminated Leishmania infection in HIV-1-infected individuals.