Human soluble TREM-1: lung and serum levels in patients with bacterial ventilator associated pneumonia

Human soluble triggering receptor expressed on myeloid cells (sTREM-1) is a glycoprotein of the immunoglobulin superfamily. In normal lung tissue, sTREM-1 is selectively expressed in lung alveolar macrophages specialized for pathogen clearance and is up-regulated in the presence of bacteria and fungi. The aim of this study was to assess sTREM-1 levels in serum and lungs of patients with ventilator associated pneumonia (VAP) and to evaluate its potential diagnostic role. The study cohort included 31 patients meeting the criteria for VAP, including clinical, microbiological, radiological and laboratory findings in patients on mechanical ventilation for more than 48 hours and with Clinical Pulmonary Infection Score (CPIS) > 6. Serum and lung levels of sTREM-1 were obtained and tested for differences. The samples were analyzed using ELISA technique and the values were expressed in pg/mL. The samples for lung sTREM-1 were obtained from direct bronchial lavage fluid and serum samples from peripheral blood. Differences were tested by Mann Whitney U test with P < 0.05 considered significant. In patients with bacterial VAP, a statistically significant difference was found between serum and lung sTREM-1 levels (P < 0.05), with very high levels of sTREM-1 recorded in lung samples (mean value 1565 pg/mL). There was no statistically significant difference in pulmonary sTREM-1 level between the polymicrobial and monomicrobial VAP groups. In conclusion, sTREM-1 is present in a high concentration in the lungs of patients with bacterial VAP. sTREM-1 levels can help in making the diagnosis of bacterial pneumonia as a standalone marker.