Ramírez, Carolina, Díaz-Toro, Yira, Tellez, Jair, Castilho, Tiago M., Rojas, Ricardo, Ettinger, Nicholas A., Tikhonova, Irina, Alexander, Neal D., Valderrama, Liliana, Hager, Janet, Wilson, Mary E., Lin, Aiping, Zhao, Hongyu, Saravia, Nancy G., and McMahon-Pratt, Diane
Background: Previous findings indicate that susceptibility to Leishmania (Viannia) panamensis infection of monocyte-derived macrophages from patients and asymptomatically infected individuals were associated with the adaptive immune response and clinical outcome. Methodology/Principal Findings: To understand the basis for this difference we examined differential gene expression of human monocyte-derived macrophages following exposure to L. (V.) panamensis. Gene activation profiles were determined using macrophages from healthy volunteers cultured with or without stationary phase promastigotes of L. (V.) panamensis. Significant changes in expression (>1.5-fold change; p<0.05; up- or down-regulated) were identified at 0.5, 4 and 24 hours. mRNA abundance profiles varied over time, with the highest level of activation occurring at earlier time points (0.5 and 4 hrs). In contrast to observations for other Leishmania species, most significantly changed mRNAs were up- rather than down-regulated, especially at early time points. Up-regulated transcripts over the first 24 hours belonged to pathways involving eicosanoid metabolism, oxidative stress, activation of PKC through G protein coupled receptors, or mechanism of gene regulation by peroxisome proliferators via PPARα. Additionally, a marked activation of Toll-receptor mediated pathways was observed. Comparison with published microarray data from macrophages infected with L. (Leishmania) chagasi indicate differences in the regulation of genes involved in signaling, motility and the immune response. Conclusions: Results show that the early (0.5 to 24 hours) human monocyte-derived macrophage response to L. (Viannia) panamensis is not quiescent, in contrast to published reports examining later response times (48–96 hours). Early macrophage responses are important for the developing cellular response at the site of infection. The kinetics and the mRNA abundance profiles induced by L. (Viannia) panamensis illustrate the dynamics of these interactions and the distinct biologic responses to different Leishmania species from the outset of infection within their primary host cell. Author Summary: Leishmania parasites cause a spectrum of diseases (cutaneous, visceral and the deforming forms—chronic cutaneous and mucocutaneous) known as leishmaniasis. The macrophage, a key cell in the immune system, is the cellular target of Leishmania parasites in the mammalian host. Previous studies showed the responses of monocytederived macrophages from naturally infected humans to infection with Leishmania (Viannia) panamensis were key to adaptive immune responses and clinical outcome. Consequently, an mRNA microarray approach was employed to assess the changes in macrophage gene expression over time (0.5 to 24 hours) induced by L. panamensis. The highest level of gene expression induction occurred early (0.5–4 hours); the early pathways (groups of genes) activated included those involved in the innate immune response (signaling, phagocytosis, TLR activation, and inflammatory). Early gene activation is presumed to be important for the developing cellular milieu at the site of infection. By 24 hours post-infection the dominant pathways involved metabolic functions. However, a comparison of the macrophage response to L. (V.) panamensis to that of L. (L.) chagasi (causative agent of visceral leishmaniasis) at 24 hours revealed a differential up-regulation of genes (cell adhesion, signaling, and inflammation) in response to these species. These observations underscore the distinct biology of different Leishmania species from the outset of infection. [ABSTRACT FROM AUTHOR]