Type 2 cytokines (IL-4, IL-5, and IL-13) play a pivotal role in helminthic infection and allergic disorders. CD4+ T cells which produce type 2 cytokines can be generated via IL-4-dependent and -independent pathways. Although the IL-4-dependent pathway is well documented, factors that drive IL-4-independent Th2 cell differentiation remain obscure. We report here that the new cytokine IL-33, in the presence of Ag, polarizes murine and human naive CD4+ T cells into a population of T cells which produce mainly IL-5 but not IL-4. This polarization requires IL-1R-related molecule and MyD88 but not IL-4 or STAT6. The IL-33-induced T cell differentiation is also dependent on the phosphorylation of MAPKs and NF-κB but not the induction of GATA3 or T-bet. In vivo, ST2−/− mice developed attenuated airway inflammation and IL-5 production in a murine model of asthma. Conversely, IL-33 administration induced the IL-5-producing T cells and exacerbated allergen-induced airway inflammation in wild-type as well as IL-4−/− mice. Finally, adoptive transfer of IL-33-polarized IL-5+IL-4−T cells triggered airway inflammation in naive IL-4−/− mice. Thus, we demonstrate here that, in the presence of Ag, IL-33 induces IL-5-producing T cells and promotes airway inflammation independent of IL-4.

Chemokines are small proteins that control several tissue functions, including cell recruitment and activation under homeostatic and inflammatory conditions. CXCL8 (interleukin-8) is a member of the chemokine family that acts on CXCR1 and CXCR2 receptors. CXCL1, CXCL2, CXCL3, CXCL5, CXCL6, and CXCL7 are also ELR+ chemokine members that bind to these receptors, especially CXCR2. The majority of studies on the biology of CXCL8 and their receptors have been performed in polymorphonuclear leukocytes. However, many other cells express CXCR1/CXCR2, including epithelial, endothelial, fibroblasts and neurons, contributing to the biological effects of CXCL8. There is substantial amount of experimental data suggesting that CXCL8 and receptors contribute to elimination of pathogens, but may also contribute significantly to disease-associated processes, including tissue injury, fibrosis, angiogenesis and tumorigenesis. Here, we discuss the biology of CXCL8 family and the potential therapeutic use of antagonists or blockers of these molecules in the context of organ-specific diseases.

Objective Host–microbial interactions are central in health and disease. Monosodium urate monohydrate (MSU) crystals cause gout by activating the NLRP3 inflammasome, leading to interleukin‐1β (IL‐1β) production and neutrophil recruitment. This study was undertaken to investigate the relevance of gut microbiota, acetate, and the metabolite‐sensing receptor GPR43 in regulating inflammation in a murine model of gout. Methods Gout was induced by the injection of MSU crystals into the knee joints of mice. Macrophages from the various animals were stimulated to determine inflammasome activation and production of reactive oxygen species (ROS). Results Injection of MSU crystals caused joint inflammation, as seen by neutrophil influx, hypernociception, and production of IL‐1β and CXCL1. These parameters were greatly decreased in germ‐free mice, mice treated with antibiotics, and GPR‐43–deficient mice. Recolonization or administration of acetate to germ‐free mice restored inflammation in response to injection of MSU crystals. In vitro, macrophages produced ROS and assembled the inflammasome when stimulated with MSU. Macrophages from germ‐free animals produced little ROS, and there was little inflammasome assembly. Similar results were observed in macrophages from GPR‐43–deficient mice. Treatment of germ‐free mice with acetate restored in vitro responsiveness of macrophages to MSU crystals. Conclusion In the absence of microbiota, there is decreased production of short‐chain fatty acids that are necessary for adequate inflammasome assembly and IL‐1β production in a manner that is at least partially dependent on GPR43. These results clearly show that the commensal microbiota shapes the host's ability to respond to an inflammasome‐dependent acute inflammatory stimulus outside the gut.

PDE4 inhibitors are effective anti-inflammatory drugs whose effects and putative mechanisms on resolution of inflammation and neutrophil apoptosis in vivo are still unclear. Here, we examined the effects of specific PDE4 inhibition on the resolution of neutrophilic inflammation in the pleural cavity of LPS-challenged mice. LPS induced neutrophil recruitment that was increased at 4 h, peaked at 8-24 h, and declined thereafter. Such an event in the pleural cavity was preceded by increased levels of KC and MIP-2 at 1 and 2 h. Treatment with the PDE4 inhibitor rolipram, at 4 h after LPS administration, decreased the number of neutrophils and increased the percentage of apoptotic cells in the pleural cavity in a PKA-dependent manner. Conversely, delayed treatment with a CXCR2 antagonist failed to prevent neutrophil recruitment. Forskolin and db-cAMP also decreased the number of neutrophils and increased apoptosis in the pleural cavity. The proapoptotic effect of rolipram was associated with decreased levels of the prosurvival protein Mcl-1 and increased caspase-3 cleavage. The pan-caspase inhibitor zVAD-fmk prevented rolipram-induced resolution of inflammation. LPS resulted in a time-dependent activation of Akt, which was blocked by treatment with rolipram or PI3K and Akt inhibitors, and PI3K and Akt inhibitors also enhanced apoptosis and promoted neutrophil clearance. Although LPS induced NF-kappaB activation, which was blocked by rolipram, NF-kappaB inhibitors did not promote resolution of neutrophil accumulation in this model. In conclusion, our data show that PDE4 inhibition resolves neutrophilic inflammation by promoting caspase-dependent apoptosis of inflammatory cells by targeting a PKA/PI3K/Akt-dependent survival pathway.

Key Points Plg and Pla induce macrophage reprogramming and promote resolution of acute inflammation. Plg and Pla enhance the efferocytic capacity of macrophages and override the prosurvival effect of LPS on neutrophils via annexin A1.