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Similarly to acute intestinal helminth infection, several conditions of chronic eosinophilic type 2 inflammation of mucosal surfaces, including asthma and eosinophilic esophagitis, feature robust expansions of intraepithelial mast cells (MCs). Also the hyperplastic mucosa of nasal polyposis in the context of chronic rhinosinusitis, with or without COX1 inhibitor intolerance, contains impressive numbers of intraepithelial MCs. In this issue of the JCI, Derakhshan et al. elucidate the heterogeneity of MCs in nasal polyposis and identify a transcriptional signature of TGF-β target genes expressed by the intraepithelial MC population. These MCs displayed effector functions that implicate them as pathogenetic contributors. TGF-β directed differentiation of similar MC populations also in vitro. These findings extend the emerging concept of TGF-β as a driver of type 2 inflammation at barrier surfaces.

Mast cells (MCs) influence intercellular communication during inflammation by secreting cytoplasmic granules that contain diverse mediators. Here, we have demonstrated that MCs decode different activation stimuli into spatially and temporally distinct patterns of granule secretion. Certain signals, including substance P, the complement anaphylatoxins C3a and C5a, and endothelin 1, induced human MCs rapidly to secrete small and relatively spherical granule structures, a pattern consistent with the secretion of individual granules. Conversely, activating MCs with anti-IgE increased the time partition between signaling and secretion, which was associated with a period of sustained elevation of intracellular calcium and formation of larger and more heterogeneously shaped granule structures that underwent prolonged exteriorization. Pharmacological inhibition of IKK-β during IgE-dependent stimulation strongly reduced the time partition between signaling and secretion, inhibited SNAP23/STX4 complex formation, and switched the degranulation pattern into one that resembled degranulation induced by substance P. IgE-dependent and substance P-dependent activation in vivo also induced different patterns of mouse MC degranulation that were associated with distinct local and systemic pathophysiological responses. These findings show that cytoplasmic granule secretion from MCs that occurs in response to different activating stimuli can exhibit distinct dynamics and features that are associated with distinct patterns of MC-dependent inflammation.

Interleukin-10 (IL-10) is an immunoregulatory cytokine that plays a pivotal role in modulating inflammation. IL-10 has inhibitory effects on proinflammatory cytokine production and function and ; as such, IL-10 is viewed as a potential treatment for various inflammatory diseases. However, a significant drawback of using IL-10 in clinical application is the fact that the biologically active form of IL-10 is an unstable homodimer, which has a short half-life and is easily degraded . Consequently, IL-10 therapy using recombinant native IL-10 has had only limited success in the treatment of human disease. To improve the therapeutic potential of IL-10, we have generated a novel form of IL-10, which consists of two IL-10 monomer subunits linked in a head to tail fashion by a flexible linker. We show that the linker length did not affect the expression and biological activity of the stable IL-10 molecule, which was more active than natural IL-10, both and . We confirmed that the new form of IL-10 had a much-improved temperature- and pH-dependent biological stability compared to natural IL-10. The IL-10 dimer protein binds to the IL-10 receptor similarly to the natural IL-10 protein, as shown by antibody blocking and through the genetic modifications of one monomer in the IL-10 dimer specifically at the IL-10 receptor binding site. Finally, we showed that stable IL-10 is more effective at suppressing LPS-induced-inflammation compared to the natural IL-10. In conclusion, we have developed a new stable dimer version of the IL-10 protein with improved stability and efficacy to suppress inflammation. We propose that this novel stable IL-10 dimer could serve as the basis for the development of targeted anti-inflammatory drugs.

Similarly to acute intestinal helminth infection, several conditions of chronic eosinophilic type 2 inflammation of mucosal surfaces, including asthma and eosinophilic esophagitis, feature robust expansions of intraepithelial mast cells (MCs). Also the hyperplastic mucosa of nasal polyposis in the context of chronic rhinosinusitis, with or without COX1 inhibitor intolerance, contains impressive numbers of intraepithelial MCs. In this issue of the JCI, Derakhshan et al. elucidate the heterogeneity of MCs in nasal polyposis and identify a transcriptional signature of TGF-f target genes expressed by the intraepithelial MC population. These MCs displayed effector functions that implicate them as pathogenetic contributors. TGF-f directed differentiation of similar MC populations also in vitro. These findings extend the emerging concept of TGF-f as a driver of type 2 inflammation at barrier surfaces.

Similarly to acute intestinal helminth infection, several conditions of chronic eosinophilic type 2 inflammation of mucosal surfaces, including asthma and eosinophilic esophagitis, feature robust expansions of intraepithelial mast cells (MCs). Also the hyperplastic mucosa of nasal polyposis in the context of chronic rhinosinusitis, with or without COX1 inhibitor intolerance, contains impressive numbers of intraepithelial MCs. In this issue of the JCI, Derakhshan et al. elucidate the heterogeneity of MCs in nasal polyposis and identify a transcriptional signature of TGF-[beta] target genes expressed by the intraepithelial MC population. These MCs displayed effector functions that implicate them as pathogenetic contributors. TGF-[beta] directed differentiation of similar MC populations also in vitro. These findings extend the emerging concept of TGF-[beta] as a driver of type 2 inflammation at barrier surfaces.

Hematopoietic stem cells (HSCs) produce highly diverse cell lineages. Here, we chart native lineage pathways emanating from HSCs and define their physiological regulation by computationally integrating experimental approaches for fate mapping, mitotic tracking, and single-cell RNA sequencing. We find that lineages begin to split when cells leave the tip HSC population, marked by high Sca-1 and CD201 expression. Downstream, HSCs either retain high Sca-1 expression and the ability to generate lymphocytes, or irreversibly reduce Sca-1 level and enter into erythro-myelopoiesis or thrombopoiesis. Thrombopoiesis is the sum of two pathways that make comparable contributions in steady state, a long route via multipotent progenitors and CD48 hi megakaryocyte progenitors (MkPs), and a short route from HSCs to developmentally distinct CD48 −/lo MkPs. Enhanced thrombopoietin signaling differentially accelerates the short pathway, enabling a rapid response to increasing demand. In sum, we provide a blueprint for mapping physiological differentiation fluxes from HSCs and decipher two functionally distinct pathways of native thrombopoiesis. Hematopoietic stem cells produce diverse cell lineages. Here, the authors apply single-cell RNA-seq, computational integration of non-perturbative approaches for fate-mapping, and mitotic tracking to chart lineage decisions in native hematopoiesis and identify megakaryocyte progenitors that directly link HSCs to megakaryocytes.

Neutrophil diapedesis is an immediate step following infections and injury and is driven by complex interactions between leukocytes and various components of the blood vessel wall. Here, we show that perivascular mast cells (MC) are key regulators of neutrophil behaviour within the sub-endothelial space of inflamed venules. Using confocal intravital microscopy, we observe directed abluminal neutrophil motility along pericyte processes towards perivascular MCs, a response that created neutrophil extravasation hotspots. Conversely, MC-deficiency and pharmacological or genetic blockade of IL-17A leads to impaired neutrophil sub-endothelial migration and breaching of the pericyte layer. Mechanistically, identifying MCs as a significant cellular source of IL-17A, we establish that MC-derived IL-17A regulates the enrichment of key effector molecules ICAM-1 and CXCL1 in nearby pericytes. Collectively, we identify a novel MC-IL-17A-pericyte axis as modulator of the final steps of neutrophil diapedesis, with potential translational implications for inflammatory disorders driven by increased neutrophil diapedesis. The blood vessel wall is a complex multi-layered structure, yet upon injury or infection, neutrophil leukocytes are rapidly migrating from the blood stream to the affected tissues, by a process termed diapedesis. Authors here show that the final steps of diapedesis through the outer pericyte layer is regulated by perivascular mast cells via IL-17A production.

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 ( CX3CR1 Cre IL-10  fl/fl ) or neutrophils and granulocytic myeloid-derived suppressor cells (G-MDSCs; Mrp8 Cre IL-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 Mrp8 Cre IL-10  fl/fl but not CX3CR1 Cre IL-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.

Conclusive evidence for the impact of mast cells (MCs) in skin repair is still lacking. Studies in mice examining the role of MC function in the physiology and pathology of skin regenerative processes have obtained contradictory results. To clarify the specific role of MCs in regenerative conditions, here we used a recently developed genetic mouse model that allows conditional MC ablation to examine MC-specific functions in skin. This mouse model is based on the cell type–specific expression of Cre recombinase in connective tissue–type MCs under control of the Mcpt5 promoter and the Cre-inducible diphtheria toxin receptor–mediated cell lineage ablation by diphtheria toxin. In response to excisional skin injury, genetic ablation of MCs did not affect the kinetics of reepithelialization, the formation of vascularized granulation tissue, or scar formation. Furthermore, genetic ablation of MCs failed to prevent the development of skin fibrosis upon bleomycin challenge. The amount of deposited collagen and the biochemistry of collagen fibril crosslinks within fibrotic lesions were comparable in MC-depleted and control mice. Collectively, our findings strongly suggest that significant reduction of MC numbers does not affect skin wound healing and bleomycin-induced fibrosis in mice, and provide to our knowledge previously unreported insight in the long-debated contribution of MCs in skin regenerative processes.

Current regulation of T cell receptor (TCR)-based therapeutics may require repeated testing of patients for specific HLA alleles as well as companion diagnostics development, despite the invariant nature of the HLA genotype and availability of robust clinical HLA tests. This increases the burden on patients and the organizations developing these products. We propose regulatory flexibility to facilitate the development of and access to TCR-based therapeutics.Current regulation of T cell receptor (TCR)-based therapeutics may require repeated testing of patients for specific HLA alleles as well as companion diagnostics development, despite the invariant nature of the HLA genotype and availability of robust clinical HLA tests. This increases the burden on patients and the organizations developing these products. We propose regulatory flexibility to facilitate the development of and access to TCR-based therapeutics.