Staphylococcus aureus-induced immunosuppression mediated by IL-10 and IL-27 facilitates nasal colonisation

Linking S. aureus Immune Evasion Mechanisms to Staphylococcal Vaccine Failures

Vaccination arguably remains the only long-term strategy to limit the spread of S. aureus infections and its related antibiotic resistance. To date, however, all staphylococcal vaccines tested in clinical trials have failed. In this review, we propose that the failure of S. aureus vaccines is intricately linked to prior host exposure to S. aureus and the pathogen's capacity to evade adaptive immune defenses. We suggest that non-protective immune imprints created by previous exposure to S. aureus are preferentially recalled by SA vaccines, and IL-10 induced by S. aureus plays a unique role in shaping these non-protective anti-staphylococcal immune responses. We discuss how S. aureus modifies the host immune landscape, which thereby necessitates alternative approaches to develop successful staphylococcal vaccines.

Distinct T cell signatures are associated with Staphylococcus aureus skin infection in pediatric atopic dermatitis

Atopic dermatitis (AD) is an inflammatory skin condition with a childhood prevalence of up to 25%. Microbial dysbiosis is characteristic of AD, with Staphylococcus aureus the most frequent pathogen associated with disease flares and increasingly implicated in disease pathogenesis. Therapeutics to mitigate the effects of S. aureus have had limited efficacy and S. aureus-associated temporal disease flares are synonymous with AD. An alternative approach is an anti-S. aureus vaccine, tailored to AD. Experimental vaccines have highlighted the importance of T cells in conferring protective anti-S. aureus responses; however, correlates of T cell immunity against S. aureus in AD have not been identified. We identify a systemic and cutaneous immunological signature associated with S. aureus skin infection (ADS.aureus) in a pediatric AD cohort, using a combined Bayesian multinomial analysis. ADS.aureus was most highly associated with elevated cutaneous chemokines IP10 and TARC, which preferentially direct Th1 and Th2 cells to skin. Systemic CD4+ and CD8+ T cells, except for Th2 cells, were suppressed in ADS.aureus, particularly circulating Th1, memory IL-10+ T cells, and skin-homing memory Th17 cells. Systemic γδ T cell expansion in ADS.aureus was also observed. This study suggests that augmentation of protective T cell subsets is a potential therapeutic strategy in the management of S. aureus in AD.

Metabolic diversity of human macrophages: potential influence on Staphylococcus aureus intracellular survival

Staphylococcus aureus is a leading cause of medical device-associated biofilm infections. This is influenced by the ability of S. aureus biofilm to evade the host immune response, which is partially driven by the anti-inflammatory cytokine interleukin-10 (IL-10). Here, we show that treatment of human monocyte-derived macrophages (HMDMs) with IL-10 enhanced biofilm formation, suggesting that macrophage anti-inflammatory programming likely plays an important role during the transition from planktonic to biofilm growth. To identify S. aureus genes that were important for intracellular survival in HMDMs and how this was affected by IL-10, transposon sequencing was performed. The size of the S. aureus essential genome was similar between unstimulated HMDMs and the outgrowth control (18.5% vs 18.4%, respectively, with 54.4% overlap) but increased to 22.5% in IL-10-treated macrophages, suggesting that macrophage polarization status exerts differential pressure on S. aureus. Essential genes for S. aureus survival within IL-10-polarized HMDMs were dominated by negative regulatory pathways, including nitrogen and RNA metabolism, whereas S. aureus essential genes within untreated HMDMs were enriched in biosynthetic pathways such as purine and pyrimidine biosynthesis. To explore how IL-10 altered the macrophage intracellular metabolome, targeted metabolomics was performed on HMDMs from six individual donors. IL-10 treatment led to conserved alterations in distinct metabolites that were increased (dihydroxyacetone phosphate, glyceraldehyde-3-phosphate, and acetyl-CoA) or reduced (fructose-6-phosphate, aspartic acid, and ornithine) across donors, whereas other metabolites were variable. Collectively, these findings highlight an important aspect of population-level heterogeneity in human macrophage responsiveness that should be considered when translating results to a patient population.IMPORTANCEOne mechanism that Staphylococcus aureus biofilm elicits in the host to facilitate infection persistence is the production of the anti-inflammatory cytokine interleukin-10 (IL-10). Here, we show that exposure of human monocyte-derived macrophages (HMDMs) to IL-10 promotes S. aureus biofilm formation and programs intracellular bacteria to favor catabolic pathways. Examination of intracellular metabolites in HMDMs revealed heterogeneity between donors that may explain the observed variability in essential genes for S. aureus survival based on nutrient availability for bacteria within the intracellular compartment. Collectively, these studies provide novel insights into how IL-10 polarization affects S. aureus intracellular survival in HMDMs and the importance of considering macrophage heterogeneity between human donors as a variable when examining effector mechanisms.

Staphylococcus aureus suppresses the pentose phosphate pathway in human neutrophils via the adenosine receptor A2aR to enhance intracellular survival

IMPORTANCE

Staphylococcus aureus is one of the leading causes of antimicrobial-resistant infections whose success as a pathogen is facilitated by its massive array of immune evasion tactics, including intracellular survival within critical immune cells such as neutrophils, the immune system's first line of defense. In this study, we describe a novel pathway by which intracellular S. aureus can suppress the antimicrobial capabilities of human neutrophils by using the anti-inflammatory adenosine receptor, adora2a (A2aR). We show that signaling through A2aR suppresses the pentose phosphate pathway, a metabolic pathway used to fuel the antimicrobial NADPH oxidase complex that generates reactive oxygen species (ROS). As such, neutrophils show enhanced ROS production and reduced intracellular S. aureus when treated with an A2aR inhibitor. Taken together, we identify A2aR as a potential therapeutic target for combatting intracellular S. aureus infection.

Neutrophil responsiveness to IL-10 impairs clearance of Streptococcus pneumoniae from the lungs

The early immune response to bacterial pneumonia requires a careful balance between pathogen clearance and tissue damage. The anti-inflammatory cytokine interleukin (IL)-10 is critical for restraining otherwise lethal pulmonary inflammation. However, pathogen-induced IL-10 is associated with bacterial persistence in the lungs. In this study, we used mice with myeloid cell specific deletion of IL-10R to investigate the cellular targets of IL-10 immune suppression during infection with Streptococcus pneumoniae, the most common bacterial cause of pneumonia. Our findings suggest that IL-10 restricts the neutrophil response to S. pneumoniae, as neutrophil recruitment to the lungs was elevated in myeloid IL-10 receptor (IL-10R)-deficient mice and neutrophils in the lungs of these mice were more effective at killing S. pneumoniae. Improved killing of S. pneumoniae was associated with increased production of reactive oxygen species and serine protease activity in IL-10R-deficient neutrophils. Similarly, IL-10 suppressed the ability of human neutrophils to kill S. pneumoniae. Burdens of S. pneumoniae were lower in myeloid IL-10R-deficient mice compared with wild-type mice, and adoptive transfer of IL-10R-deficient neutrophils into wild-type mice significantly improved pathogen clearance. Despite the potential for neutrophils to contribute to tissue damage, lung pathology scores were similar between genotypes. This contrasts with total IL-10 deficiency, which is associated with increased immunopathology during S. pneumoniae infection. Together, these findings identify neutrophils as a critical target of S. pneumoniae-induced immune suppression and highlight myeloid IL-10R abrogation as a mechanism to selectively reduce pathogen burdens without exacerbating pulmonary damage.

STAT3 Deficiency Alters the Macrophage Activation Pattern and Enhances Matrix Metalloproteinase 9 Expression during Staphylococcal Pneumonia

Staphylococcus aureus is a significant cause of morbidity and mortality in pulmonary infections. Patients with autosomal-dominant hyper-IgE syndrome due to STAT3 deficiency are particularly susceptible to acquiring staphylococcal pneumonia associated with lung tissue destruction. Because macrophages are involved in both pathogen defense and inflammation, we investigated the impact of murine myeloid STAT3 deficiency on the macrophage phenotype in vitro and on pathogen clearance and inflammation during murine staphylococcal pneumonia. Murine bone marrow-derived macrophages (BMDM) from STAT3 LysMCre+ knockout or Cre- wild-type littermate controls were challenged with S. aureus, LPS, IL-4, or vehicle control in vitro. Pro- and anti-inflammatory responses as well as polarization and activation markers were analyzed. Mice were infected intratracheally with S. aureus, bronchoalveolar lavage and lungs were harvested, and immunohistofluorescence was performed on lung sections. S. aureus infection of STAT3-deficient BMDM led to an increased proinflammatory cytokine release and to enhanced upregulation of costimulatory MHC class II and CD86. Murine myeloid STAT3 deficiency did not affect pathogen clearance in vitro or in vivo. Matrix metalloproteinase 9 was upregulated in Staphylococcus-treated STAT3-deficient BMDM and in lung tissues of STAT3 knockout mice infected with S. aureus. Moreover, the expression of miR-155 was increased. The enhanced inflammatory responses and upregulation of matrix metalloproteinase 9 and miR-155 expression in murine STAT3-deficient as compared with wild-type macrophages during S. aureus infections may contribute to tissue damage as observed in STAT3-deficient patients during staphylococcal pneumonia.

IL-10 production by granulocytes promotes Staphylococcus aureus craniotomy infection

BACKGROUND

Treatment of brain tumors, epilepsy, or hemodynamic abnormalities requires a craniotomy to access the brain. Nearly 1 million craniotomies are performed in the US annually, which increase to ~ 14 million worldwide and despite prophylaxis, infectious complications after craniotomy range from 1 to 3%. Approximately half are caused by Staphylococcus aureus (S. aureus), which forms a biofilm on the bone flap that is recalcitrant to antibiotics and immune-mediated clearance. However, the mechanisms responsible for the persistence of craniotomy infection remain largely unknown. The current study examined the role of IL-10 in promoting bacterial survival.

METHODS

A mouse model of S. aureus craniotomy infection was used with wild type (WT), IL-10 knockout (KO), and IL-10 conditional KO mice where IL-10 was absent in microglia and monocytes/macrophages (CX3CR1CreIL-10 fl/fl) or neutrophils and granulocytic myeloid-derived suppressor cells (G-MDSCs; Mrp8CreIL-10 fl/fl), the major immune cell populations in the infected brain vs. subcutaneous galea, respectively. Mice were examined at various intervals post-infection to quantify bacterial burden, leukocyte recruitment, and inflammatory mediator production in the brain and galea to assess the role of IL-10 in craniotomy persistence. In addition, the role of G-MDSC-derived IL-10 on neutrophil activity was examined.

RESULTS

Granulocytes (neutrophils and G-MDSCs) were the major producers of IL-10 during craniotomy infection. Bacterial burden was significantly reduced in IL-10 KO mice in the brain and galea at day 14 post-infection compared to WT animals, concomitant with increased CD4+ and γδ T cell recruitment and cytokine/chemokine production, indicative of a heightened proinflammatory response. S. aureus burden was reduced in Mrp8CreIL-10 fl/fl but not CX3CR1CreIL-10 fl/fl mice that was reversed following treatment with exogenous IL-10, suggesting that granulocyte-derived IL-10 was important for promoting S. aureus craniotomy infection. This was likely due, in part, to IL-10 production by G-MDSCs that inhibited neutrophil bactericidal activity and TNF production.

CONCLUSION

Collectively, these findings reveal a novel role for granulocyte-derived IL-10 in suppressing S. aureus clearance during craniotomy infection, which is one mechanism to account for biofilm persistence.