Resolvin D2 promotes host defense in a 2 - hit model of sepsis with secondary lung infection

In the development of sepsis, there is early, massive inflammation which can lead to multiple organ failure. Later there is an immunosuppressed phase where the host is susceptible to secondary infections or is unable to clear existing infection. Specialized Pro-resolving Mediators (SPMs) are endogenously produced lipids which resolve infection by decreasing bacteria load and reducing systemic inflammatory response. There has been little work studying if SPMs given late, can promote host defense. We examined if an SPM, Resolvin D2 (RvD2) could promote host defense in a 2-hit mouse model of cecal ligation and puncture (CLP) sepsis and secondary Pseudomonas aeruginosa lung infection. RvD2 given 48 h after mild CLP (1st hit), increased gene expression of Toll-like receptor-2 (TLR-2) and alveolar macrophage/monocyte phagocytic ability compared to CLP mice given saline vehicle. In this model, RvD2 did not affect plasma IL-6 or IL-10. These effects induced by RvD2, lowered lung bacterial load and decreased mortality after the secondary infection of Pseudomonas aeruginosa (2nd hit). Splenic T-cell numbers were also increased in RvD2 treated mice compared to saline vehicle treated animals. The results suggest that RvD2 promoted mechanisms of host defense in a 2-hit model sepsis and secondary lung infection.