Objective To observe the changes of soluble triggering receptor expressed on myeloid cell-1 ( sTREM-1) and inflammatory mediators levels in plasma of severe pneumonia patients, and explore the significance of systemic inflammatory response state.Methods Plasma levels of sTREM-1, tumor necrosis factor-α ( TNF-α) and interleukin-10 ( IL-10) were examined in 40 patients with severe pneumonia, 25 patients with uncomplicated pneumonia, and 15 healthy volunteers. Plasma levels of TNF-α,IL-10 and sTREM-1 in survival and non-survival severe pneumoniawere observed on days 1,4, 7 and the day of discharge or death.Results Plasma levels of TNF-α, IL-10, and sTREM-1 [ ( 44. 25 ±10. 81) pg/mL,( 58. 21 ±16. 41) pg/mL, ( 51. 75 ±18. 51) pg/mL, respectively] in the patients with severe pneumonia were higher than those with uncomplicated pneumonia [ ( 24.6 ±6. 45) pg/mL, ( 24. 56 ±7. 1) pg/mL,( 25. 55 ±7. 72) pg/mL, respectively] and the normal controls [ ( 13. 82 ±4. 04) pg/mL, ( 15. 30 ±4. 45)pg/mL, ( 14. 37 ±4. 82) pg/mL, respectively] ( P lt;0. 001) . Plasma levels of TNF-α, IL-10, and sTREM-1 were gradually decreased in the survivors, while maintained at high levels or increased in the non-survivors.The levels of these mediators were all significantly higher in the non-survivors than the survivors at all time points. The ratio of TNF-α/ IL-10 level was higher in the severe pneumonia patients than the uncomplicated pneumonia patients and the control subjects ( 1. 286 ±0. 177 vs. 1. 077 ±0. 410 and 0. 932 ±0. 154) on day 1.The ratio of TNF-α/IL-10 level was higher in the non-survivors than the survivors at all time points. There was negative correlation between plasma levels of sTREM-1 and TNF-αon day 1 ( r = - 0. 479, P =0. 002) ,and positive correlation between plasma levels of sTREM-1 and IL-10 on day 1 ( r = 0. 326, P = 0. 040) .Conclusions There are excessive release of inflammatory mediators and unbalanced systemic inflammatory response in patients with severe pneumonia, especially in non-survivors. sTREM-1, TNF-α and IL-10 are involved in the inflammatory response, and their levels may reflect the prognosis.