Serum activity of indoleamine 2,3-dioxygenase predicts prognosis of community-acquired pneumonia

Objectives Indoleamine 2,3-dioxygenase (IDO) catalyzes the rate-limiting step of tryptophan (Trp) degradation in the kynurenine (Kyn) pathway. By depleting Trp, IDO plays a critical role in inducing immune suppression and tolerance. The aim of present study was to investigate serum IDO activity, determined by Kyn-to-Trp ratio (Kyn/Trp ratio), in community-acquired pneumonia (CAP) and to examine its clinical significance. Metods This study subjects consisted of 129 consecutive patients with CAP and 64 healthy controls. The concentrations of Kyn and Trp were measured simultaneously by liquid chromatography/electrospray ionization tandem mass spectrometry. Results The CAP patients had significantly higher Kyn concentrations and significant lower Trp concentrations than the controls (p < 0.0001 and p < 0.0001, respectively). Accordingly, IDO activity was significantly higher (2.4-fold) in the patients than in the controls (p < 0.0001). IDO activity correlated well with PSI (Pneumonia Severity Index) and CURB65 (p = 0.0005 and p < 0.0001, respectively). Moreover, the IDO activity and Kyn concentration were significantly higher in the nonsurvivors and were found to predict mortality in multivariate analysis. Conclusions IDO activity was increased in CAP, and this activity was associated with the severity and outcome of this disease. These results suggest that IDO activity can predict prognosis of CAP.