Lipoxin A4 impairs effective bacterial control and potentiates joint inflammation and damage caused by Staphylococcus aureus infection

Staphylococcus aureus is the main cause of septic arthritis in humans, a disease associated with high morbidity and mortality. Inflammation triggered in response to infection is fundamental to control bacterial growth but may cause permanent tissue damage. Here, we evaluated the role of Lipoxin A₄ (LXA₄ ) in S aureus-induced arthritis in mice. Septic arthritis was induced by S aureus injection into tibiofemoral joints. At different time points, we evaluated cell recruitment and bacterial load in the joint, the production of pro-inflammatory molecules, and LXA₄ in inflamed tissue and analyzed joint damage and dysfunction. LXA₄ was investigated using genetically modified mice or by pharmacological blockade of its synthesis and receptor. CD11c⁺ cells were evaluated in lymph nodes by confocal microscopy and flow cytometry and dendritic cell chemotaxis using the Boyden chamber. Absence or pharmacological blockade of 5-lipoxygenase (5-LO) reduced joint inflammation and dysfunction and was associated with better control of infection at 4 to 7 days after the infection. There was an increase in LXA₄ in joints of S aureus-infected mice and administration of LXA₄ reversed the phenotype in 5-LO^-/- mice. Blockade or absence of the LXA₄ receptor FPR2 has a phenotype similar to 5-LO^-/- mice. Mechanistically, LXA₄ appeared to control migration and function of dendritic cells, cells shown to be crucial for adequate protective responses in the model. Thus, after the first days of infection when symptoms become evident therapies that inhibit LXA₄ synthesis or action could be useful for treatment of S aureus-induced arthritis.

SOCS2 modulates adipose tissue inflammation and expansion in mice

INTRODUCTION

Obesity is usually triggered by a nutrient overload that favors adipocyte hypertrophy and increases the number of pro-inflammatory cells and mediators into adipose tissue. These mediators may be regulated by suppressors of cytokine signaling (SOCS), such as SOCS2, which is involved in the regulation of the inflammatory response of many diseases, but its role in obesity is not yet known. We aimed to investigate the role of SOCS2 in metabolic and inflammatory dysfunction induced by a high-refined carbohydrate-containing diet (HC).

MATERIAL AND METHODS

Male C57BL/6 wild type (WT) and SOCS2 deficient (SOCS2^-/-) mice were fed chow or an HC diet for 8 weeks.

RESULTS

In general, SOCS2 deficient mice, independent of the diet, showed higher adipose tissue mass compared with their WT counterparts that were associated with decreased lipogenesis rate in adipose tissue, lipolysis in adipocyte culture and energy expenditure. An anti-inflammatory profile was observed in adipose tissue of SOCS2^-/- by reduced secretion of cytokines, such as TNF and IL-6, and increased M2-like macrophages and regulatory T cells compared with WT mice. Also, SOCS2 deficiency reduced the differentiation/expansion of pro-inflammatory cells in the spleen but increased Th2 and Treg cells compared with their WT counterparts.

CONCLUSION

The SOCS2 protein is an important modulator of obesity that regulates the metabolic pathways related to adipocyte size. Additionally, SOCS2 is an inflammatory regulator that appears to be essential for controlling the release of cytokines and the differentiation/recruitment of cells into adipose tissue during the development of obesity.

The role of mTOR, TRAF1, and local antigen in 4-1BB-dependent establishment of Trm in the lung

The tumour necrosis factor receptor (TNFR) superfamily receptor 4-1BB is important in the establishment of a tissue-resident memory (Trm) population in the lung tissue following influenza infection. Moreover, supraphysiological boosting of 4-1BB during the boost phase of a prime-boost immunization regimen can greatly enhance the establishment of a long-lived Trm population that protects against lethal heterotypic challenge (Zhou et al. Mucosal Immunology 2017). However, little is known about how 4-1BB contributes to the establishment of the lung Trm population. Here, we investigated the mechanism by which 4-1BB induces lung Trm cells. Using competitive mixed bone marrow chimeras, we found that the effect of 4-1BB on lung resident influenza-specific T cells does not substantially change between day 9 and 45 post-infection, suggesting that the main effect of 4-1BB is to allow the persistence of CD8 T effector cells as they transition to Trm. The signaling adaptor TRAF1, downstream of 4-1BB was also shown to be important in enhancing the numbers of Teffectors and Trm in the lung. Using supraphysiological stimulation of 4-1BB in the boost phase of a prime boost immunization, we show 4-1BB-mediated Trm generation is dependent on local delivery of both antigen and costimulation and that this process is inhibited by rapamycin, suggesting a role for mTOR in this process. Also, using this prime-boost model we demonstrate that TRAF1 contributes to the effect of 4-1BB on Trm generation. Taken together, these data point to an important role for 4-1BB, TRAF1 and mTORC1 in allowing the lung effector T cells in the lung parenchyma to survive through the transition to tissue resident memory T cells.

This work was funded by CIHR grant FDN-143250 to THW

Prolonged ingestion of ovalbumin diet by sensitized mice improves the metabolic consequences induced by experimental food allergy

The prevalence of food allergy is rising in the western world. Allergen restriction is the chosen treatment in this condition, but continuous ingestion of the antigen has shown positive results in clinical trials. In a previous study, we have shown several allergic and metabolic alterations after 7 days of ovalbumin (OVA) ingestion by sensitized mice. The aim of this study was to investigate whether prolonged ingestion of antigen by sensitized mice would reverse the metabolic consequences caused by experimental food allergy. For this, allergic and metabolic parameters were analysed after prolonged ingestion of an OVA diet by OVA-sensitized mice. As shown previously, after 7 days of OVA consumption, sensitized mice showed increased serum levels of anti-OVA immunoglobulin (Ig)E and IgG1, aversion to the antigen ingestion, marked body and adipose tissue weight loss, followed by adipose tissue inflammation and decreased serum levels of adipokines, glucose and triglycerides. However, after 14 days of oral challenge, sensitized mice showed an anti-OVA IgE level similar to the mice that were only sensitized, but the specific IgG1 did not change. With this prolonged ingestion of OVA, sensitized mice were protected from OVA-induced anaphylaxis when the antigen was given systemically at a dose of 2 mg/animal. Moreover, various parameters analysed were significantly ameliorated, including adipose tissue inflammation, body and adipose tissue loss, as well as serum levels of adipokines and triglycerides. Therefore, our data suggest that prolonged ingestion of OVA by sensitized mice results in an improvement of the metabolic consequences caused by experimental food allergy.