Macrophage and T-Cell Gene Expression in a Model of Early Infection with the Protozoan Leishmania chagasi

Nicholas A Ettinger; Mary E Wilson

doi:10.1371/journal.pntd.0000252

Visceral leishmaniasis is a potentially fatal infectious disease caused by the protozoan parasite Leishmania infantum/chagasi in the New World, or by L. donovani or L. infantum/chagasi in the Old World. Infection leads to a variety of outcomes ranging from asymptomatic infection to active disease, characterized by fevers, cachexia, hepatosplenomegaly and suppressed immune responses. We reasoned that events occurring during the initial few hours when the parasite encounters cells of the innate and adaptive immune systems are likely to influence the eventual immune response that develops. Therefore, we performed gene expression analysis using Affymetrix U133Plus2 microarray chips to investigate a model of early infection with human monocyte-derived macrophages (MDMs) challenged with wild-type L. chagasi parasites, with or without subsequent co-culture with Leishmania-naïve, autologous T-cells. Microarray data generated from total RNA were analyzed with software from the Bioconductor Project and functional clustering and pathway analysis were performed with DAVID and Gene Set Enrichment Analysis (GSEA), respectively. Many transcripts were down-regulated by infection in cultures containing macrophages alone, and the pattern indicated a lack of a classically activated phenotype. By contrast, the addition of autologous Leishmania-naïve T cells to infected macrophages resulted in a pattern of gene expression including many markers of type 1 immune cytokine activation (IFN-γ, IL-6, IL-1α, IL-1β). There was simultaneous up-regulation of a few markers of immune modulation (IL-10 cytokine accumulation; TGF-β Signaling Pathway). We suggest that the initial encounter between L. chagasi and cells of the innate and adaptive immune system stimulates primarily type 1 immune cytokine responses, despite a lack of classical macrophage activation. This local microenvironment at the site of parasite inoculation may determine the initial course of immune T-cell development. Visceral leishmaniasis (VL) is a potentially fatal vector-borne infectious disease that leads to a variety of outcomes ranging from asymptomatic infection to symptomatic disease. In northeast Brazil, the etiological agent of VL is the protozoan Leishmania chagasi/infantum . Active VL is characterized by fevers, weight loss, hepatosplenomegaly and eventually immune suppression. Without treatment, most symptomatic patients die from secondary bacterial or viral super-infection. We hypothesized that a unique immune response to L. chagasi is initiated early during the initial interactions between the immune system cells that first encounter the parasite. These include macrophages and T-cells, elements of the innate and adaptive immune systems, respectively. We studied an in vitro model of these interactions in which human monocyte-derived macrophages were challenged with L. chagasi , and subsequently cultured with Leishmania-naïve, autologous T cells. Using microarray chips, we examined changes in global gene expression induced by these early interactions. Infection did not elicit a classical inflammatory program in macrophages. However, co-culture of infected macrophages and autologous T cells exhibited a pattern of gene expression, including many markers of acute inflammation or a type 1 immune response. These data suggest that early changes at the site of parasite infection would be conducive to the development of a protective type 1 response, followed by modulation of this same response.

Macrophage and T-Cell Gene Expression in a Model of Early Infection with the Protozoan Leishmania chagasi

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