Soluble triggering receptor expressed on myeloid cells in sputum of patients with community-acquired pneumonia or pulmonary tuberculosis: a pilot study

Soluble triggering receptor expressed on myeloid cells (s-TREM-1) is upregulated on the surface of inflammatory cells in the presence of bacterial infections, apparently excluding those due to Mycobacterium tuberculosis. Therefore, sputum concentrations of s-TREM-1 may be of value in distinguishing bacterial pneumonia from pulmonary tuberculosis (PTB) in patients with respiratory infections. The current pilot study was designed to evaluate whether s-TREM-1 concentrations measured in the sputum of patients with suspected community-acquired pneumonia (CAP) allowed differentiation of those patients with PTB from other causes of pneumonia and to correlate s-TREM-1 with CURB-65, a marker of disease severity. Soluble s-TREM-1 concentrations were measured in sputum samples from patients admitted to a tertiary hospital with CAP or PTB by means of an ELISA procedure. Soluble-TREM-1 was readily detectable and quantifiable in sputum samples from patients with both CAP and PTB, with concentrations of 234 ± 47 and 178 ± 36 pg/ml respectively, but did not differ significantly between the two groups. However, patients with PTB had significantly lower leukocyte counts, 9 ± 1.3 vs 15 ± 1.4 × 10⁹/l compared with those without PTB. Interestingly, sputum s-TREM-1 concentrations correlated significantly with the CURB-65 pneumonia severity score calculated at the time of admission. Soluble-TREM-1 expression is upregulated in patients with both CAP and PTB, but does not differentiate between these two conditions. Sputum concentrations of s-TREM-1 may predict the severity of disease in patients with CAP.