Orientia tsutsugamushi Stimulates an Original Gene Expression Program in Monocytes: Relationship with Gene Expression in Patients with Scrub Typhus

Abstract

Orientia tsutsugamushi is the causal agent of scrub typhus, a public health problem in the Asia-Pacific region and a life-threatening disease. O. tsutsugamushi is an obligate intracellular bacterium that mainly infects endothelial cells. We demonstrated here that O. tsutsugamushi also replicated in monocytes isolated from healthy donors. In addition, O. tsutsugamushi altered the expression of more than 4,500 genes, as demonstrated by microarray analysis. The expression of type I interferon, interferon-stimulated genes and genes associated with the M1 polarization of macrophages was significantly upregulated. O. tsutsugamushi also induced the expression of apoptosis-related genes and promoted cell death in a small percentage of monocytes. Live organisms were indispensable to the type I interferon response and apoptosis and enhanced the expression of M1-associated cytokines. These data were related to the transcriptional changes detected in mononuclear cells isolated from patients with scrub typhus. Here, the microarray analyses revealed the upregulation of 613 genes, which included interferon-related genes, and some features of M1 polarization were observed in these patients, similar to what was observed in O. tsutsugamushi-stimulated monocytes in vitro. This is the first report demonstrating that monocytes are clearly polarized in vitro and ex vivo following exposure to O. tsutsugamushi. These results would improve our understanding of the pathogenesis of scrub typhus, during which interferon-mediated activation of monocytes and their subsequent polarization into an M1 phenotype appear critical. This study may give us a clue of new tools for the diagnosis of patients with scrub typhus.

Reply to Tantibhedhyangkul et al., ‘Suspected Mycoplasma Contamination in the Study “Toll-Like Receptor 2 Recognizes Orientia tsutsugamushi and Increases Susceptibility to Murine Experimental Scrub Typhus”’

“…Moreover, Tantibhedhyangkul et al claim that live Orientia bacteria generally induce higher levels of cytokines in monocytes and macrophages than inactivated organisms do (7,8). This is in contrast not only to our data (1) but also to previous work that demonstrated increased production of tumor necrosis factor alpha (TNF-␣) and interleukin-6 by murine macrophages that were stimulated with heat-killed Orientia organisms rather than infected with live Orientia organisms (9).…”

Activation of Indoleamine 2,3-Dioxygenase in Patients with Scrub Typhus and Its Role in Growth Restriction of Orientia tsutsugamushi

“…From our earlier analysis of genome-wide expression, we have observed an up-regulation of IDO1 in peripheral blood leukocytes of patients with acute scrub typhus [10]. Thus, activation of IDO1 was first confirmed at functional level in patients with acute scrub typhus in the present study.…”

“…Considering that monocytes appear to be the main source of active IDO1 in human peripheral blood [42], [43], THP-1 cells were used as an experimental model of infection in further testing of our hypothesis. Indeed, up-regulation of IDO-1 was previously demonstrated in OT-infected monocyte-derived macrophages [10]. Besides, we believe that macrophages could be a secondary target of infection to harbour the intracellular organisms to remote organs; which was supported by the detection of OT in circulating monocyte-like blood cells of patients with acute scrub typhus [48] and in macrophages located in the liver, the spleen, and the lymph nodes of fatal cases of scrub typhus [49], [50].…”

Placental Macrophages Are Impaired in Chorioamnionitis, an Infectious Pathology of the Placenta

“…The M1/M2 polarization status of pMw and MGCs was determined by qRT-PCR as described above. The 9 M1-related and 10 M2-related genes were selected from lists of M1 and M2 genes published elsewhere (35,36). The results are presented as radar plots.…”