• Pseudomonas aeruginosa (2) • Interstitial lung disease (6) • Other (4 specificity to diagnose between a pulmonary infiltrate of infectious origin and a pulmonary infiltrate of non-infectious origin were 82.6% and 75.9% respectively for mTREM-1 above 3.05 MFI. AUC of CRP was 0.789 ± 0.065(95%CI: 0.66 -0.9, p < 0.001). Sensitivity and specificity to diagnose between a pulmonary infiltrate of infectious origin and a pulmonary infiltrate of non-infectious origin were 78% and 76% respectively at concentrations above 8.7 mg/ml. Positive correlations were found between APACHE II scores and expression of TREM-1 on monocytes on day 1 (r s : +0.363, p: 0.010); and between APACHE II scores and sTREM-1 on day 1 (r s : +0.262, p: 0.043). No significant correlations were found between APACHE II scores and expression of TREM-1 on neutrophils on day 1 as well as between SOFA scores and any of the measured parameters on day 1.