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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.

Acute high-altitude (HA) exposure can induce several pathologies. Dexamethasone (DEX) can be taken prophylactically to prevent HA disease, but the mechanism by which it acts in this setting is unclear. We studied the transcriptome of peripheral blood mononuclear cells (PBMCs) from 16 subjects at low altitude (LA, 225 m) and then 3 days after acute travel to HA (3500 m) during the India-Leh-Dexamethasone-Expedition-2020 (INDEX2020). Half of the participants received oral DEX prophylaxis 4 mg twice daily in an unblinded manner, starting 1 day prior to travel to HA, and 12 h prior to the first PBMC collection. PBMC transcriptome data were obtained from 16 subjects, half of whom received DEX. The principal component analysis demonstrated a clear separation of the groups by altitude and treatment. HA exposure resulted in a large number of gene expression changes, particularly in pathways of inflammation or the regulation of cell division, translation, or transcription. DEX prophylaxis resulted in changes in fewer genes, particularly in immune pathways. The gene sets modulated by HA and DEX were distinct. Deconvolution analysis to assess PBMC subpopulations suggested changes in B-cell, T-cell, dendritic cell, and myeloid cell numbers with HA and DEX exposures. Acute HA travel and DEX prophylaxis induce significant changes in the PBMC transcriptome. The observed benefit of DEX prophylaxis against HA disease may be mediated by suppression of inflammatory pathways and changing leukocyte population distributions.

Whether all Schistosoma species cause pulmonary hypertension (PH) is unclear. Experimentally exposing mice to Schistosoma haematobium eggs caused PH, which was less severe than that induced by S. mansoni exposure. These findings align with the relatively uncommon reports of pulmonary arterial hypertension associated with S. haematobium.

Schistosomiasis 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. Mice 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. Flow cytometry and scRNAseq both identified 3 IM subpopulations, characterized by CCR2, MHCII, and FOLR2 expression. Following exposure, the CCR2 IM subpopulation expanded, suggestive of circulating monocyte recruitment. 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. -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.

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.

Pathologic implications of dysregulated pulmonary vascular metabolism to pulmonary arterial hypertension (PAH) are increasingly recognized, but their clinical applications have been limited. We hypothesized that metabolite quantification across the pulmonary vascular bed in connective tissue disease–associated (CTD-associated) PAH would identify transpulmonary gradients of pathobiologically relevant metabolites, in an exercise stage–specific manner. Sixty-three CTD patients with established or suspected PAH underwent exercise right heart catheterization. Using mass spectrometry–based metabolomics, metabolites were quantified in plasma samples simultaneously collected from the pulmonary and radial arteries at baseline and during resistance-free wheeling, peak exercise, and recovery. We identified uptake and excretion of metabolites across the pulmonary vascular bed, unique and distinct from single vascular site analysis. We demonstrated the physiological relevance of metabolites previously shown to promote disease in animal models and end-stage human lung tissues, including acylcarnitines, glycolytic intermediates, and tryptophan catabolites. Notably, pulmonary vascular metabolite handling was exercise stage specific. Transpulmonary metabolite gradients correlated with hemodynamic endpoints largely during free-wheeling. Glycolytic intermediates demonstrated physiologic significance at peak exercise, including net uptake of lactate in those with more advanced disease. Contribution of pulmonary vascular metabolism to CTD-PAH pathogenesis and therapeutic candidacy of metabolism modulation must be considered in the context of physiologic stress.

Dendritic cells (DCs) are key sentinels in the lung mucosa that interpret environmental signals to either promote tolerance or trigger inflammation, influencing the development of chronic lung diseases. This review highlights recent mechanistic insights showing that metabolic checkpoints serve as upstream regulators of DC fate and activity: inflammatory stimuli activate HIF-1α/mTOR-linked glycolytic pathways that drive maturation, cytokine secretion, antigen presentation, and migration. In contrast, AMPK-related oxidative and lipid metabolism pathways support tolerogenic states that encourage regulatory T-cell responses and inhibit checkpoints like PD-1/PD-L1. We also present evidence that DC subset specialization (cDC1 vs. cDC2) and their tissue location interact with these metabolic pathways to regulate lymphoid tissue formation, including the development and persistence of tertiary lymphoid structures in chronically inflamed lungs. These ectopic lymphoid tissues enhance local immune responses through DC–stromal interactions and ongoing T follicular helper–B cell communication, contributing to persistent inflammation and tissue remodeling in conditions such as COPD, asthma, pulmonary hypertension, and fibrotic interstitial lung disease. Finally, we discuss the translational potential of targeting this immunometabolic–lymphoid pathway, suggesting that modulating metabolic regulators, migratory circuits, and tolerogenic programs could restore immune balance while maintaining host defense—a promising framework for developing advanced therapies for chronic lung inflammation.