Triggering receptor expressed on myeloid cells-1 in pleural effusions: a marker of inflammatory disease.

Background: Triggering receptor expressed on myeloid cells (TREM)-1 is a recently described molecule that plays an important role in myeloid cell-activated inflammatory responses. The aim of this study was to investigate the expression of TREM-1 in pleural effusions of various causes.

Methods: For this cross-sectional, observational study conducted between February and August 2005 in Taiwan, 74 patients with pleural effusions of varying etiology were investigated. Soluble TREM-1 (sTREM-1) was measured in pleural fluid samples, and cells in the fluid were assessed for surface expression of TREM-1.

Results: Concentrations of sTREM-1 were significantly higher in infectious and neoplastic pleural effusions (189.1+/-36.7 and 69.9+/-22.8ng/ml, mean+/-sem) than in transudates (10.1+/-5.3ng/ml; P<0.001). Among infectious effusions, the sTREM-1 levels were significantly higher in parapneumonic than in tuberculous effusions (301.8+/-49.8 vs. 38.9+/-17.3ng/ml; P<0.001). TREM-1 was expressed on a portion of the myeloid (CD11b positive) cells in each type of effusion, without significant differences among them (transudative, 34.7%; neoplastic, 36.0%; parapneumonic, 27.7%; tuberculous, 21.2%; P=0.861). Non-myeloid cells expressed very little TREM-1 (transudative, 6.3%; neoplastic, 0.5%; parapneumonic, 1.0%; tuberculous, 0.7%; P=0.192).

Conclusions: sTREM-1 expression in pleural fluids is highest in parapneumonic and neoplastic effusions but low in transudates. In infectious effusions, a high concentration of sTREM-1 may exclude tuberculous pleurisy.