The IL-1b/CXCL1/2/neutrophil axis mediates host protection against group B streptococcal infection

Previous studies have indicated that group B streptococcus (GBS), a frequent human pathogen, potently induces the release of IL-1β, an important mediator of inflammatory responses. Since little 26 is known about the role of this cytokine in GBS disease, we analyzed the outcome of infection in 27 IL-1β-deficient mice. These animals were markedly sensitive to GBS infection, with most of them 28 dying under challenge conditions that caused no deaths in wild type control mice. Lethality was due to the inability of the IL-1β-deficient mice to control local GBS replication and dissemination to target organs, such as the brain and the kidneys. Moreover, in a model of inflammation induced by 31 the intraperitoneal injection of killed GBS, lack of IL-1β was associated with a selective impairment 32 in the production of the neutrophil chemokines CXCL1 and CXCL2 and in neutrophil recruitment to the peritoneal cavity. Decreased blood neutrophil counts and impaired neutrophil recruitment to the brain and kidneys were also observed during GBS infection in IL-1β-deficient mice, concomitantly with a reduction in CXCL1 and CXCL2 tissue levels. Notably, the hypersusceptibility to GBS infection observed in the immune deficient animals was recapitulated by neutrophil depletion with anti-Gr1 antibodies. Collectively our data identify a cytokine circuit that involves IL-1β-induced production of CXCL1 and CXCL2 and leads the recruitment of neutrophils to GBS infection sites. Moreover our data point to an essential role of these cells in controlling the progression and outcome of GBS disease.