Novel CD11b(+)Gr-1(+)Sca-1(+) myeloid cells drive mortality in bacterial infection

Extreme pathophysiological stressors induce expansion of otherwise infrequent leukocyte populations. Here, we found a previously unidentified CD11b(+)Gr-1(+) myeloid cell population that expresses stem cell antigen-1 (Sca-1) induced upon experimental infection with Staphylococcus aureus. Although CD11b(+)Gr-1(+)Sca-1(+) cells have impaired migratory capacity and superoxide anion–producing activity, they secrete increased levels of several cytokines and chemokines compared to Sca-1(−) counterparts. The generation of CD11b(+)Gr-1(+)Sca-1(+) cells is dependent on IFN-γ in vivo, and in vitro stimulation of bone marrow cells or granulocyte-macrophage progenitors with IFN-γ generated CD11b(+)Gr-1(+)Sca-1(+) cells. Depletion of CD11b(+)Gr-1(+)Sca-1(+) cells by administrating anti–Sca-1 antibody strongly increased survival rates in an S. aureus infection model by reducing organ damage and inflammatory cytokines. However, adoptive transfer of CD11b(+)Gr-1(+)Sca-1(+) cells decreased survival rates by worsening the pathogenesis of S. aureus infection. Together, we found a previously unidentified pathogenic CD11b(+)Gr-1(+)Sca-1(+) population that plays an essential role in mortality during bacterial infection.