Abstract
Macrophages are the principal host cells of Leishmania spp . in human infection and play a critical role in controlling infection and enabling parasite survival and persistence. Nevertheless, understanding of drug resistance in leishmaniasis has primarily focused on the parasite. This investigation provides evidence of the significant differential macrophage response to ex vivo infection with clinical strains of L. (V . ) panamensis naturally resistant (zymodeme 2.3/zym 2.3) or sensitive (zymodeme 2.2/zym 2.2) to antimonial drug, and the distinct effect of this drug on the activation of macrophages. Transcriptome analysis of infected monocyte-derived macrophages from healthy donors revealed significant interferon responses and cytokine signaling by zym 2.3 strains compared to zym 2.2 strains. Furthermore, in the presence of antimony, macrophages infected with zym 2.3 strains, but not with zym 2.2 strains, significantly increased the expression of genes associated with M-CSF-generated macrophages (M-MØ, anti-inflammatory). Notably, macrophages infected with zym 2.3 strains exhibited elevated expression of genes associated with homeostasis and microbicidal regulation, such as the IDO1/IL4I1-Kyn-AHR pathways and superoxide dismutase, and downregulation of transporters like ABC and AQP , compared to macrophages infected with zym 2.2 strains. Remarkably, the majority of these pathways remained upregulated even in the presence of the strong modulatory effect of antimonial drug. Together, these findings demonstrate that the initial and specific parasite-host interaction influences the ex vivo macrophage response to antimony. Identification of key pathways in macrophage responses associated with natural resistance to this antileishmanial, enhances understanding of host-response mechanisms in the outcome of Leishmania infection and response to treatment. IMPORTANCE: Drug resistance and treatment failure are increasingly recognized in human leishmaniasis. Investigation of resistance has predominantly focused on parasite-mediated mechanisms. This study examines the role of host macrophages in natural resistance to antimonial drug. Our findings reveal distinct responses by macrophages infected with Leishmania (Viannia) panamensis strains that are naturally resistant to antimonial drug versus sensitive strains, both in the presence and absence of the drug. Distinctively, resistant parasites induced regulatory pathways that modulate inflammatory responses and alter host cell transporter expression, potentially contributing to parasite survival under antimony exposure. The host cell-parasite interaction in the context of drug resistant intracellular infections presents opportunities for innovative therapeutic strategies targeting host cell responses. GRAPHICAL ABSTRACT: Clinical strains of L. (V . ) panamensis naturally resistant or sensitive to antimonial drug (SbV) induce different profiles of human macrophage activation. L. (V . ) panamensis strains with natural SbV resistance induce a significant interferon response in macrophages, accompanied by overexpression of the IDO1 / IL4I1 - Kyn - AHR pathways and SOD2 , associated with immune homeostasis and regulation of microbicidal activity. Homeostatic regulation by the IDO1 / IL4I1 - Kyn - AHR pathways, induced in macrophages by infection with naturally SbV-resistant strains of L. (V . ) panamensis , prevails despite significant modulation of macrophage activation by antimony exposure. Antimony treatment promotes a more anti-inflammatory (M-MØ) profile in macrophages infected with naturally resistant L. (V . ) panamensis strains, while macrophages infected with sensitive strains maintain a more proinflammatory profile (GM-MØ). Infection with the zym 2.3 strains in the presence of SbV leads to downregulation of specific macrophage transporter genes, supporting the capacity of these naturally SbV-resistant parasites to elicit macrophage responses that enable antimony resistance.