Hypoxia is a major cause of pulmonary hypertension (PH) worldwide, and it is likely that interstitial pulmonary macrophages contribute to this vascular pathology. We observed in hypoxia-exposed mice an increase in resident interstitial macrophages, which expanded through proliferation and expressed the monocyte recruitment ligand CCL2. We also observed an increase in CCR2+ macrophages through recruitment, which express the protein thrombospondin-1, which functionally activates TGF-β to cause vascular disease. Blockade of monocyte recruitment with either CCL2-neutralizing antibody treatment or CCR2 deficiency in the bone marrow compartment suppressed hypoxic PH. These data were supported by analysis of plasma samples from humans who traveled from low (225 m) to high (3500 m) elevation, revealing an increase in thrombospondin-1 and TGF-β expression following ascent, which was blocked by dexamethasone prophylaxis. In the hypoxic mouse model, dexamethasone prophylaxis recapitulated these findings by mechanistically suppressing CCL2 expression and CCR2+ monocyte recruitment. These data suggest a pathologic cross talk between 2 discrete interstitial macrophage populations, which can be therapeutically targeted.

Public health alarm concerning the emerging fungus Candida auris is fueled by its antifungal drug resistance and propensity to cause deadly outbreaks. Persistent skin colonization drives transmission and lethal sepsis although its basis remains mysterious. We compared the skin colonization dynamics of C. auris with its relative C. albicans, quantifying skin fungal persistence and distribution and immune composition and positioning. C. auris displayed a higher propensity to colonize hair follicles and avidly bound to human hair. While C. albicans triggered an effective sterilizing type 3/17 antifungal immune response driven by IL-17A/F-producing lymphocytes, C. auris triggered a type 1, IFNγ-driven immune response targeting hair follicles. Rather than promoting fungal clearance, IFNγ enhanced C. auris skin colonization by acting directly on keratinocytes impairing epithelial barrier integrity and repressing antifungal defense programs. C. auris exploits focal skin immune responses to create a niche for persistence in hair follicles.

Interactions between the nervous and immune systems are critical to healthy physiology and are altered in many human diseases. Many of the major players in type 2 immune responses, including type 2 lymphocytes and cytokines, mast cells, and immunoglobulin E, have been implicated in neuronal function and behavior. Conversely, neurons in both the central and peripheral nervous systems can affect type 2 immune responses and behaviors relevant to allergy, such as food avoidance. Defining this complex circuitry and its molecular intermediates in physiology may reveal type 2 immunomodulators that can be harnessed for therapeutic benefit in neurologic diseases including Alzheimer's disease, brain injury, and neurodevelopmental disorders. Conversely, modulation of the nervous system may be an important adjunct to treating immunologic disorders including atopic dermatitis, asthma, and food allergy. This Review covers recent work defining how the nervous system can both regulate and be regulated by type 2 immune responses.

Background: Schistosomiasis is a major cause of pulmonary hypertension (PH) worldwide, and CD4 T cells are critical in disease pathogenesis. The role of dendritic cells (DCs) in Schistosoma-induced PH (SchPH) is unknown. There are two types of conventional DCs, cDC1 and cDC2, that prototypically activate CD8 and CD4 T cells, respectively. Methods: We exposed wildtype, DC reporter, and DC knockout mice to Schistosoma mansoni and quantified PH severity by heart catheterization and cell density by flow cytometry. Results: Experimental S. mansoni exposure increased the density of pulmonary DCs, particularly cDC2s. Deleting both cDC subsets did not significantly modify SchPH disease severity. Deleting only cDC1s caused more severe SchPH, associated with more Th2 CD4 and CD8 T cells. In contrast, deleting only cDC2s reduced SchPH disease severity. Conclusions: cDC1s appear to be protective, whereas cDC2s promote disease in SchPH.

Idiopathic pulmonary fibrosis (IPF) is a disease of progressive lung remodeling and collagen deposition that leads to respiratory failure. Myeloid cells are abundant in IPF lung and in murine lung fibrosis, but their functional effects are incompletely understood. Using mouse and human lung models, we show that ornithine produced by myeloid cells expressing arginase 1 (ARG1) serves as a substrate for proline and collagen synthesis by lung fibroblasts. The predominant ARG1-expressing myeloid cells in mouse lung were macrophages, but in IPF lung, high-dimensional imaging revealed ARG1 was expressed mainly in neutrophils. Small-molecule ARG1 inhibition suppressed both ornithine levels and collagen expression in cultured, precision-cut IPF lung slices and in murine lung fibrosis. These results were confirmed in macrophage-specific Arg1-KO mice. Furthermore, we found that this pathway is regulated by cell-to-cell crosstalk, starting with purinergic signaling: extracellular ATP receptor P2RX4 was necessary for fibroblast IL-6 expression, which, in turn, was necessary for ARG1 expression by myeloid cells. Taken together, our findings define an immune-mesenchymal circuit that governs profibrotic metabolism in lung fibrosis.

Rationale: Idiopathic pulmonary fibrosis (IPF) is a disease of progressive lung remodeling and collagen deposition that leads to respiratory failure and need for lung transplantation. Recent studies have revealed clusters of inflammatory fibroblasts that are present in both animal models of fibrosis and in IPF. However, the function of these cells, or how they are induced by the microenvironment of injury, is completely unknown. We recently found that mice with fibroblast-specific KO of eATP receptor P2rx4 were protected from lung fibrosis. Here we tested whether P2rx4 regulates inflammatory pathways that determine injury-induced fibrosis. Methods: scRNAseq, lung biochemical analysis, genetic modification, multiplexed ion beam imaging (MIBI), and metabolomic analysis were applied to study macrophage-fibroblast interactions in the lung in the setting of injury-induced fibrosis. Results: Studies in mice with fibroblast-specific deletion of P2rx4 revealed that eATP-P2rx4 signaling was necessary for fibroblast expression of the inflammatory cytokine IL-6. IL-6, in turn, induced myeloid cell expression of Arg1. Arg1 inhibition and deletion resulted in decreased fibrosis in the bleomycin model and decreased fibroblast proline content, while conversely supplementation of the arginase reaction product ornithine was found to increase levels of proline and collagen in vitro and in vivo. Imaging of protein expression in IPF lung samples with a 40-marker MIBI panel revealed increased ARG1+ cells compared to healthy controls, and ARG1 was expressed in the neutrophil compartment. Xenium proximity analysis showing ARG1+ and IL6+ fibroblasts at closer proximity, compared to IL6- fibroblasts. Arginase inhibition suppressed collagen expression in cultured precision-cut IPF lung slices. Discussion: We identify crosstalk necessary for fibrosis, characterized by the induction of myeloid Arg1 by a pro-inflammatory purinergic pathway in fibroblasts dependent on eATP-P2rx4 signaling, which regulated IL-6 expression. In mouse models, Arg1 contributed to fibrotic responses by metabolizing arginine to ornithine, which fibroblasts used as a substrate to synthesize proline driving collagen expression. Taken together, these findings define, for the first time to our knowledge, an immune-mesenchymal circuit that governs profibrotic metabolism in lung fibrosis. Neutrophilia has been linked to mortality in IPF, and our data provides a mechanism for fibrotic progression attributable to ARG1+ neutrophils.

Fibroblasts and immune cells coordinate tissue regeneration and necessary scarring after injury. In the brain, fibroblasts are border-enriched cells whose dynamic molecular states and immune interactions after injury remain unclear1. Here we define the shared fibroblast-immune response to brain injury. Early profibrotic myofibroblasts develop from pre-existing brain fibroblasts and infiltrate brain lesions, orchestrated by fibroblast TGFβ signalling, profibrotic macrophages and microglia, and perilesional glia. Myofibroblasts transition into several late fibroblast states, including lymphocyte-interactive fibroblasts. Interruption of the early myofibroblast state exacerbated sub-acute brain injury, tissue loss and secondary neuroinflammation, with increased mortality in the transient middle cerebral artery occlusion stroke model. Disruption of late lymphocyte-fibroblast niches via selective loss of fibroblast chemokine CXCL12 led to late brain-specific innate inflammation and lymphocyte dispersal with increased IFNγ production. These data indicate the response to brain injury is coordinated by evolving temporal and spatial fibroblast states that limit functional tissue loss and chronic neuroinflammation.

Pulmonary conventional dendritic cells (cDCs) are functionally and phenotypically heterogeneous antigen-presenting cells essential for orchestrating adaptive immune responses in the lung. Here, we define a cell-intrinsic role for granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling in the development of a CD301b+ subset of terminally differentiated cDC2s, in addition to CD103+XCR1+ cDC1s. Unbiased single-cell transcriptomic profiling of CD11c+ cells identified both immature and differentiated lung cDC populations. GM-CSF deficiency disrupted antiapoptotic Bcl2a1 up-regulation and impaired progression to the CD301b+ transcriptional state. Despite the positioning of CD301b+ cDC2s in lymphoid cell-rich adventitial cuff areas, hematopoietic GM-CSF was dispensable for their development. Instead, alveolar epithelial type 2 cell-derived GM-CSF was required for CD301b+ cDC2 formation and pulmonary type 2 immune responses, highlighting the central role of GM-CSF signaling in shaping the pulmonary myeloid landscape.

AbstractPublic health alarm concerning the emerging fungusCandida aurisis fueled by its antifungal drug resistance and propensity to cause deadly outbreaks. Persistent skin colonization drives transmission and lethal sepsis although its basis remains mysterious. We compared the skin colonization dynamics ofC. auriswith its relativeC. albicans, quantifying skin fungal persistence and distribution and immune composition and positioning.C. aurisdisplayed a higher propensity to colonize hair follicles and avidly bound to human hair. WhileC. albicanstriggered an effective sterilizing type 3/17 antifungal immune response driven by IL-17A/F-producing lymphocytes,C. auristriggered a type 1, IFNγ-driven immune response targeting hair follicles. Rather than promoting fungal clearance, IFNγ enhancedC. aurisskin colonization by acting directly on keratinocytes impairing epithelial barrier integrity and repressing antifungal defense programs.C. aurisexploits focal skin immune responses to create a niche for persistence in hair follicles.

Genetic engineering of T cells in mouse models is essential for investigating immune mechanisms. We aimed to develop an approach to manipulate T cells in vivo using an evolved adeno-associated virus (AAV) capsid named Ark313. Delivery of a transient transgene expression cassette was feasible using Ark313, and this serotype outperformed natural serotypes. A single intravenous injection of a Cre recombinase-expressing Ark313 in the Ai9 fluorescent reporter mouse model achieved permanent genetic modifications of T cells. Ark313 facilitated in vivo gene editing in both tissue-resident and splenic T cells and validation of immunotherapy targets in solid tumor models. Ark313 delivered large DNA donor templates to T cells in vivo and integrated transgenes in primary CD4+ and CD8+ T cells, including naive T cells. Ark313-mediated transgene delivery presents an efficient approach to target mouse T cells in vivo and a resource for the interrogation of T cell biology and for immunotherapy applications.

Fibroblasts coordinate the response to tissue injury, directing organ regeneration versus scarring. In the central nervous system (CNS), fibroblasts are uncommon cells enriched at tissue borders, and their molecular, cellular, and functional interactions after brain injury are poorly understood. Here we define the fibroblast response to sterile brain damage across time and space. Early pro-fibrotic myofibroblasts infiltrated CNS lesions and were functionally and spatially organized by fibroblast TGFβsignaling, pro-fibrotic macrophages and microglia, and perilesional brain glia that activated TGFβvia integrinαvβ8. Early myofibroblasts subsequently transitioned into a variety of late states, including meningeal and lymphocyte-interactive fibroblasts that persisted long term. Interruption of this dynamic fibroblast-macrophage-glial coordination impaired brain wound healing and the resolution of neuroinflammation, disrupted generation of latede novoCNS lymphocyte niches, and increased mortality in a stroke model. This work highlights an unexpected role of fibroblasts as coordinate regulators of CNS healing and neuroinflammation after brain injury.

BackgroundSchistosomiasis is a common cause of pulmonary hypertension (PH) worldwide. Type 2 inflammation contributes to the development of Schistosoma-induced PH. Specifically, interstitial macrophages (IMs) derived from monocytes play a pivotal role by producing thrombospondin-1 (TSP-1), which in turn activates TGF-β, thereby driving the pathology of PH. Resident and recruited IM subpopulations have recently been identified. We hypothesized that in Schistosoma-PH, one IM subpopulation expresses monocyte recruitment factors, whereas recruited monocytes become a separate IM subpopulation that expresses TSP-1.MethodsMice were intraperitoneally sensitized and then intravenously challenged with S. mansoni eggs. Flow cytometry on lungs and blood was performed on wildtype and reporter mice to identify IM subpopulations and protein expression. Single-cell RNA sequencing (scRNAseq) was performed on flow-sorted IMs from unexposed and at day 1, 3 and 7 following Schistosoma exposure to complement flow cytometry based IM characterization and identify gene expression.ResultsFlow cytometry and scRNAseq both identified 3 IM subpopulations, characterized by CCR2, MHCII, and FOLR2 expression. Following Schistosoma exposure, the CCR2+ IM subpopulation expanded, suggestive of circulating monocyte recruitment. Schistosoma exposure caused increased monocyte-recruitment ligand CCL2 expression in the resident FOLR2+ IM subpopulation. In contrast, the vascular pathology-driving protein TSP-1 was greatest in the CCR2+ IM subpopulation.ConclusionSchistosoma-induced PH involves crosstalk between IM subpopulations, with increased expression of monocyte recruitment ligands by resident FOLR2+ IMs, and the recruitment of CCR2+ IMs which express TSP-1 that activates TGF-β and causes PH.

Traumatic brain injury (TBI) is a leading cause of mortality and disability worldwide and can lead to secondary sequelae such as increased seizure susceptibility. Emerging work suggests that the thalamus, the relay center of the brain that undergoes secondary damage after cortical TBI, is involved with heightened seizure risks after TBI. TBI also induces the recruitment of peripheral immune cells, including T cells, to the site(s) of injury, but it is unclear how these cells impact neurological sequelae post-TBI. Here, we characterize the identities and kinetics of lymphocytic infiltrates into the cortex and thalamus using a mouse model of cortical TBI. We identify a population of IFNγ-producing type 1 lymphocytes that infiltrate specific thalamic subregions over weeks following injury, where they elicit a local IFNγ response in microglia and neuronal subset(s). Depletion of CD4 + T cells protects mice from TBI-induced seizure susceptibility by de-repressing other non-CD4 + type 1 lymphocytes and disease-associated microglia (DAMs) in the thalamus. Strikingly, we find that a single dose of IFNγ prior to challenge with a proconvulsant agent was sufficient to reduce TBI-induced seizure incidence, severity, and mortality. This work identifies IFNγ as a direct modulator of TBI-associated seizure susceptibility, which could have therapeutic implications for the treatment of TBI patients.

Background: Schistosomiasis is a parasitic infection that can cause pulmonary hypertension (PH). Th2 CD4 T cells are necessary for experimental Schistosoma-PH. However, if T cells migrate to the lung to initiate, the localized inflammation that drives vascular remodeling and PH is unknown. Methods: Mice were sensitized to Schistosoma mansoni eggs intraperitoneally and then challenged using tail vein injection. FTY720 was administered, which blocks lymphocyte egress from lymph nodes. T cells were quantified using flow cytometry, PH severity via heart catheterization, and cytokine concentration through ELISA. Results: FTY720 decreased T cells in the peripheral blood, and increased T cells in the mediastinal lymph nodes. However, FTY720 treatment resulted in no change in PH or type 2 inflammation severity in mice sensitized and challenged with S. mansoni eggs, and the number of memory and effector CD4 T cells in the lung parenchyma was also unchanged. Notably, intraperitoneal Schistosoma egg sensitization alone resulted in a significant increase in intravascular lymphocytes and T cells, including memory T cells, although there was no significant change in parenchymal cell density, IL-4 or IL-13 expression, or PH. Conclusion: Blocking T cell migration did not suppress PH following Schistosoma egg challenge. Memory CD4 T cells, located in the lung intravascular space following egg sensitization, appear sufficient to cause type 2 inflammation and PH.

The innate immune system shapes brain development and is implicated in neurodevelopmental diseases. It is critical to define the relevant immune cells and signals and their impact on brain circuits. In this work, we found that group 2 innate lymphoid cells (ILC2s) and their cytokine interleukin-13 (IL-13) signaled directly to inhibitory interneurons to increase inhibitory synapse density in the developing mouse brain. ILC2s expanded and produced IL-13 in the developing brain meninges. Loss of ILC2s or IL-13 signaling to interneurons decreased inhibitory, but not excitatory, cortical synapses. Conversely, ILC2s and IL-13 were sufficient to increase inhibitory synapses. Loss of this signaling pathway led to selective impairments in social interaction. These data define a type 2 neuroimmune circuit in early life that shapes inhibitory synapse development and behavior.

Pulmonary hypertension (PH) is a chronic and progressive disease with significant morbidity and mortality. It is characterized by remodeled pulmonary vessels associated with perivascular and intravascular accumulation of inflammatory cells. Although there is compelling evidence that bone marrow-derived cells, such as macrophages and T cells, cluster in the vicinity of pulmonary vascular lesions in humans and contribute to PH development in different animal models, the role of dendritic cells in PH is less clear. Dendritic cells' involvement in PH is likely since they are responsible for coordinating innate and adaptive immune responses. We hypothesized that dendritic cells drive hypoxic PH. We demonstrate that a classical dendritic cell (cDC) subset (cDC2) is increased and activated in wild-type mouse lungs after hypoxia exposure. We observe significant protection after the depletion of cDCs in ZBTB46 DTR chimera mice before hypoxia exposure and after established hypoxic PH. In addition, we find that cDC depletion is associated with a reduced number of two macrophage subsets in the lung (FolR2+ MHCII+ CCR2+ and FolR2+ MHCII+ CCR2-). We found that depleting cDC2s, but not cDC1s, was protective against hypoxic PH. Finally, proof-of-concept studies in human lungs show increased perivascular cDC2s in patients with Idiopathic Pulmonary Arterial Hypertension (IPAH). Our data points to an essential role of cDCs, particularly cDC2s, in the pathophysiology of experimental PH.

Group 2 innate lymphoid cells (ILC2s) cooperate with adaptive Th2 cells as key organizers of tissue type 2 immune responses, while a spectrum of innate and adaptive lymphocytes coordinate early type 3/17 immunity. Both type 2 and type 3/17 lymphocyte associated cytokines are linked to tissue fibrosis, but how their dynamic and spatial topographies may direct beneficial or pathologic organ remodelling is unclear. Here we used volumetric imaging in models of liver fibrosis, finding accumulation of periportal and fibrotic tract IL-5 + lymphocytes, predominantly ILC2s, in close proximity to expanded type 3/17 lymphocytes and IL-33 high niche fibroblasts. Ablation of IL-5 + lymphocytes worsened carbon tetrachloride-and bile duct ligation-induced liver fibrosis with increased niche IL-17A + type 3/17 lymphocytes, predominantly γδ T cells. In contrast, concurrent ablation of IL-5 + and IL-17A + lymphocytes reduced this progressive liver fibrosis, suggesting a cross-regulation of type 2 and type 3 lymphocytes at specialized fibroblast niches that tunes hepatic fibrosis.

Although mice normally enter labor when their ovaries stop producing progesterone (luteolysis), parturition can also be triggered in this species through uterus-intrinsic pathways potentially analogous to the ones that trigger parturition in humans. Such pathways, however, remain largely undefined in both species. Here, we report that mice deficient in innate type 2 immunity experienced profound parturition delays when manipulated endocrinologically to circumvent luteolysis, thus obliging them to enter labor through uterus-intrinsic pathways. We found that these pathways were in part driven by the alarmin IL-33 produced by uterine interstitial fibroblasts. We also implicated important roles for uterine group 2 innate lymphoid cells, which demonstrated IL-33-dependent activation prior to labor onset, and eosinophils, which displayed evidence of elevated turnover in the prepartum uterus. These findings reveal a role for innate type 2 immunity in controlling the timing of labor onset through a cascade potentially relevant to human parturition.

When monocyte-derived macrophages are recruited to injured tissues, they can induce a maladaptive fibrotic response characterized by excessive production of fibrillar collagen from local fibroblasts. Macrophages initiate the fibrotic programming of fibroblasts via paracrine factors, but it is unclear if reciprocal responses from the fibroblasts trigger pro-fibrotic programming of macrophages to establish a collaborative feed-forward fibrotic circuit. We identify macrophage-fibroblast cross talk necessary for injury-associated fibrosis, in which macrophages induce interleukin 6 ( IL-6 ) expression in fibroblasts via purinergic receptor P2rx4 signaling and IL-6 induces arginase 1 ( Arg1 ) expression in macrophages. Surprisingly, Arg1 contributes to fibrotic responses by metabolizing arginine to ornithine, which fibroblasts use as a substrate to synthesize proline, a uniquely abundant constituent of fibrillar collagen. Taken together, we define a bidirectional circuit between macrophages and fibroblasts that facilitates cross-feeding metabolism necessary for injury-associated fibrosis.### Competing Interest StatementThe authors have declared no competing interest.