Human macrophage response to L. (Viannia) panamensis: microarray evidence for an early inflammatory response

Abstract

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.

Figure 1. Variation of up- and down-regulated transcripts with time post-infection.

A) The number of gene transcripts up- or down-regulated at 0.5, 4 and 24 hours post-infection/interaction with Leishmania (Viannia) panamensis promastigotes are schematically summarized. The decreasing response of the up-regulated gene transcripts with time is evident; the number of down-regulated genes is relatively consistent across the time points. B) The numbers of gene transcripts in common or differentially expressed at each time point. Gene transcript expression comparisons were made between infected and uninfected macrophages for each individual at the different time points. Gene transcripts with average intensity values less than 2× background intensity for both comparison groups, or fold change less than 1.5 fold (up or down-regulated) were excluded in further statistical analysis. A paired t test using p-value cutoff 0.05 was applied to determine if a gene was statistically differentially expressed.