Partial relationships (partial correlation using residuals of the best models selected in Table 1) between the richness of infectious diseases and (A) the richness of bird and mammal species and (B) population size (partial correlation of the best GLM selected in Table 1).

<p>Partial relationships (partial correlation using residuals of the best models selected in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090032#pone-0090032-t001" target="_blank">Table 1</a>) between the richness of infectious diseases and (A) the richness of bird and mammal species and (B) population size (partial correlation of the best GLM selected in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090032#pone-0090032-t001" target="_blank">Table 1</a>).</p

Relationships between the number of diseases causing outbreaks and biodiversity indices in Asia-Pacific countries (partial correlations of the best GLM selected in Table 2).

<p>A. Total number of infectious diseases with outbreaks and number of threatened vertebrate species. B. Total zoonotic diseases with outbreaks and number of threatened vertebrate species. C. Total number of vector-borne diseases with outbreaks and forest cover.</p

Increase in total outbreaks and total number of infectious diseases causing outbreaks since 1950 in Asia-Pacific countries.

<p>Increase in total outbreaks and total number of infectious diseases causing outbreaks since 1950 in Asia-Pacific countries.</p

Assessment of IDO1 activity in patients' sera.

<p>Serum concentrations of L-Trp (A) and L-Kyn (B) in patients with scrub typhus (n = 20) were compared with those in healthy donors (n = 10). L-Kyn/L-Trp ratios (C) were calculated to reflect IDO1 activity. Data were derived from triplicate measurement. Median and interquantile range are presented.</p

Kinetics of IDO1 expression in THP-1 cells.

<p>Before being infected with OT, THP-1 cells were treated with IFN-γ alone, IFN-γ combined with 1-MT, or neither. Mock-infected THP-1 cells were used as a control. Fold induction represents levels of IDO1 expression in each culture condition at indicated time points relative to that in mock-infected cells at 6 hours p.i.. For clearer illustration, data of OT-infected and mock-infected cultures are exclusively presented in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001731#pntd-0001731-g002" target="_blank">Figure 2A</a>, and those of all four culture conditions are shown in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001731#pntd-0001731-g002" target="_blank">Figure 2B</a>. Means ± SEM from triplicate cultures are shown.</p

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

<div><h3>Background</h3><p>Our earlier genome-wide expression study revealed up-regulation of a tryptophan-catabolizing enzyme, indoleamine 2,3-dioxygenase (IDO1), in patients with scrub typhus. This gene has been previously reported to have anti-microbial activity in a variety of infectious diseases; therefore, we aimed to prove whether it is also involved in host defense against <em>Orientia tsutsugamushi</em> (OT) infection.</p> <h3>Methodology/Principal Findings</h3><p>Using LC-MS, we observed an increased ratio of serum L-kynurenine to serum L-tryptophan in patients with scrub typhus, which suggests an active catalytic function of this enzyme upon the illness. To evaluate the effect of IDO1 activation on OT infection, a human macrophage-like cell line THP-1 was used as a study model. Although transcription of IDO1 was induced by OT infection, its functional activity was not significantly enhanced unless the cells were pretreated with IFN-γ, a potent inducer of IDO1. When the degree of infection was evaluated by quantitative real-time PCR, the relative number of OT 47 kDa gene per host genes, or infection index, was markedly reduced by IFN-γ treatment as compared to the untreated cultures at five days post-infection. Inhibition of IDO1 activity in IFN-γ treated cultures by 1-methyl-L-tryptophan, a competitive inhibitor of IDO1, resulted in partial restoration of infection index; while excessive supplementation of L-tryptophan in IFN-γ treated cultures raised the index to an even higher level than that of the untreated ones. Altogether, these data implied that IDO1 was partly involved in restriction of OT growth caused by IFN-γ through deprivation of tryptophan.</p> <h3>Conclusions/Significance</h3><p>Activation of IDO1 appeared to be a defensive mechanism downstream of IFN-γ that limited intracellular expansion of OT via tryptophan depletion. Our work provided not only the first link of in vivo activation of IDO1 and IFN-γ-mediated protection against OT infection but also highlighted the promise of this multifaceted gene in scrub typhus research.</p> </div

Summarized results for a General Linear Model explaining the number of infectious diseases with epidemics (total, zoonotic and vector-borne) in Asia-Pacific.

<p>Initial variables were: nation area size, population size, richness of bird and mammal species, number of threatened vertebrate species, proportion of forest, mean temperature, mean precipitation, surveys, GDP and health expenditure. Selection of the best models was based on AIC criterion (see all models in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090032#pone.0090032.s002" target="_blank">File S2</a>). Selected variables are ranked by increasing contribution to the model (F value). The multicollinearity among independent variables is assessed by the variance inflated factor (VIF).</p

Figure 1

<p>A. Correlation among geographic (latitude, evapotranspiration, nation area size), climate (mean temperature, mean precipitation), and socio-economic variables (population size, GPD <i>per capita</i>, health expenditure), and health surveys, potentially linked with the richness infectious diseases and their outbreaks (see raw data in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090032#pone.0090032.s001" target="_blank">File S1</a>): B. Principal Component Analysis on geographic (latitude, evapotranspiration, nation area size), biodiversity (bird and mammal richness, forest cover, vertebrate species at threat), climate (mean temperature, mean precipitation), and socio-economic variables (population size, GPD <i>per capita</i>, health expenditure), and health surveys, potentially linked with the richness infectious diseases. Distributions of variables were normalized using log-transformation or asin-square root transformation (see raw data in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090032#pone.0090032.s001" target="_blank">File S1</a>).</p

Clinical and laboratory characteristics of the patients with scrub typhus.

<p>IQR = interquantile range, DIC = disseminated intravascular coagulopathy, AST = aspartate aminotansferase, ALT = alanine aminotransferase.</p

Assessment of OT growth in THP-1 cultures.

<p>Before being infected with OT, THP-1 cells were treated with IFN-γ alone, IFN-γ combined with 1-MT, or IFN-γ supplemented with L-Trp at 400 µg/ml (A) or 1 mg/ml (B). The infection index represents the degree of OT growth in each culture condition at indicated time points relative to that in mock-infected cells at 1 day p.i.. Means ± SEM from triplicate cultures are shown.</p