BackgroundSepsis is a major healthcare problem and current estimates suggest that the incidence of sepsis is approximately 750,000 annually. Sepsis is caused by an inability of the immune system to eliminate invading pathogens. It was recently proposed that endogenous mediators produced during sepsis can contribute to the immune dysfunction that is observed in sepsis. Endocannabinoids that are produced excessively in sepsis are potential factors leading to immune dysfunction, because they suppress immune cell function by binding to G-protein-coupled CB2 receptors on immune cells. Here we examined the role of CB2 receptors in regulating the host's response to sepsis.Methods and FindingsThe role of CB2 receptors was studied by subjecting CB2 receptor wild-type and knockout mice to bacterial sepsis induced by cecal ligation and puncture. We report that CB2 receptor inactivation by knockout decreases sepsis-induced mortality, and bacterial translocation into the bloodstream of septic animals. Furthermore, CB2 receptor inactivation decreases kidney and muscle injury, suppresses splenic nuclear factor (NF)-κB activation, and diminishes the production of IL-10, IL-6 and MIP-2. Finally, CB2 receptor deficiency prevents apoptosis in lymphoid organs and augments the number of CD11b+ and CD19+ cells during CLP.ConclusionsTaken together, our results establish for the first time that CB2 receptors are important contributors to septic immune dysfunction and mortality, indicating that CB2 receptors may be therapeutically targeted for the benefit of patients suffering from sepsis.

IRAK1 is a key regulatory protein in TLR/IL1R-mediated cell activation during the inflammatory response. Studies indicated that pending on the nature of the used inflammatory model, down-regulation of IRAK1 may be beneficial or detrimental. However the role of IRAK1 in affecting outcome in polymicrobial sepsis is unknown. We tested this question using an IRAK1 deficient mouse strain and the cecal ligation and puncture (CLP) procedure, which is a clinically relevant rodent septic model. Sepsis-induced mortality was markedly lower in IRAK1-deficient mice (35%) compared to WT (85%). Sepsis-induced increases in blood IL-6 and IL-10 levels were blunted at 6h post-CLP in IRAK1 deficiency compared to WT but cytokine levels were similar at 20h post-CLP. Sepsis induced blood granulocytosis and depletion of splenic B cells were also blunted in IRAK1 deficient mice as compared to WT. Analysis of TLR-mediated cytokine responses by IRAK1 deficient and WT macrophages ex vivo indicated a TLR4-dependent down-regulation of IL-6 and IL1β in IRAK1 deficiency, whereas TLR2 dependent responses were unaffected. TLR7/8-mediated IL-6, IL1β and IL-10 production was also blunted in IRAK1 macrophages as compared to WT. The study shows that IRAK1 deficiency impacts multiple TLR-dependent pathways and decreases early cytokine responses following polymicrobial sepsis. The delayed inflammatory response caused by the lack of IRAK1 expression is beneficial, as it manifests a markedly increased chance of survival after polymicrobial sepsis.

Cellular X chromosome mosaicism, which is unique to females may be advantageous during pathophysiological challenges as compared to the single X chromosome machinery of males and may also contribute to gender dimorphism in the inflammatory response. We tested the hypothesis whether cellular mosaicism for the X-linked gp91phox (NOX2) deficiency, the catalytic component of the superoxide anion generating NADPH oxidase complex, is advantageous during polymicrobial sepsis. Deficient, WT and heterozygous/mosaic mice were compared following polymicrobial sepsis initiated by cecal ligation and puncture. As compared to WT littermates, sepsis-induced mortality was improved in deficient mice, as well as, in mosaics animals carrying deficient and WT phagocyte subpopulations simultaneously. In contrast, blood bacterial counts were the highest in deficient mice as compared to mosaic or WT animals. Consistent with poor survival, WT mice also showed the worst organ damage following sepsis. In mosaic animals, the deficient neutrophil subpopulations displayed increased organ recruitment and elevated CD11b membrane expression as compared to WT neutrophil subpopulations within the same animal. The dynamics of sepsis-induced blood and organ cytokine content and white blood cell composition changes including lymphocyte subsets in blood and BM showed differences among WT, deficient and mosaic subjects indicating that mosaic mice are not simply the average of the deficient and WT responses. Upon oxidative burst, interchange of oxidants between WT and deficient neutrophil subpopulations occurred in mosaic mice. The study suggests that mice mosaic for gp91phox expression have multiple advantages in comparison to WT as well as deficient mice during the septic course.

Objective-To test the hypothesis, using an animal model, whether female X-chromosome mosaicism for inflammatory gene expression could contribute to the gender dimorphic response during the host response. X-chromosome-linked genetic polymorphisms present a unique biological condition because females display heterozygous cellular mosaicism, due to the fact that either the maternal or the paternal X chromosomes are inactivated in each individual cell in females. This is in contrast with the conditions in males who carry exclusively the maternal X chromosome. Design-Prospective, randomized, laboratory investigation. Settings-University research laboratory.Subjects-Female mice deficient, heterozygous (mosaic) or WT for the X-linked gp91phox.Interventions-We compared selected inflammatory markers among heterozygous (mosaics), WT and homozygous deficient animals in response to in vivo lipopolysaccharide (Escherichia coli, 20 mg/kg body weight). To test individual mosaic subpopulations of polymorphonuclear neutrophil responses, we also developed a flow cytometry assay that identifies the active parental X chromosomes in individual cells, using gp91phox expression as a marker. Measurements and MainResults-Heterozygous mosaic mice presented white blood cell trafficking patterns similar to that observed in WT mice, despite the fact that the deficient subpopulation in mosaic animals displayed increased cell activation as reflected in elevated neutrophil CD11b expression and splenic infiltration. Mosaic animals also displayed splenic neutrophil infiltration, which was skewed toward the deficient subpopulation. Observations on splenic T-cell depletion and post lipopolysaccharide interleukin-10 responses indicated that the inflammatory response in mosaic animals does not simply display an average of the deficient and WT responses, but the mosaic subjects display a uniquely characteristic response.Conclusions-The study supports the notion that female X chromosome mosaicism for polymorphic gene expression represents a unique condition, which may contribute to the gender dimorphic character of the inflammatory response. Mosaicism for X-linked polymorphisms may have clinical significance and needs consideration in genetic association or gender-related clinical studies.