Siglec-F+ neutrophils in the spleen induce immunosuppression following acute infection

The mechanisms underlying the increased mortality of secondary infections during the immunosuppressive phase of sepsis remain elusive. We established a mouse model of sepsis-induced immunosuppression followed by secondary infection. Compared to other organs, we observed a significant reduction in pro-inflammatory cytokines in the spleen, accompanied by a marked increase in IL-10 production, primarily by infiltrating neutrophils. Furthermore, we confirmed that these infiltrating neutrophils in the spleen during the immunosuppressive phase of sepsis undergo phenotypic change in the local microenvironment, exhibiting high expression of neutrophil biomarkers such as Siglec-F, Ly6G, and Siglec-E. These neutrophils subsequently produced IL-10 to suppress T lymphocytes. Depletion of neutrophils or specifically targeting Siglec-F leads to a notable improvement in the survival of mice with secondary infections. The identification of Siglec-F+ neutrophils as key regulators of immunosuppression following sepsis represents a novel finding with potential therapeutic implications. To investigate the mechanism underlying the increased mortality of secondary infections, we established a mouse model of sepsis-induced immunosuppression followed by secondary infection.