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Immune-mediated diseases are characterized by aberrant immune responses, posing significant challenges to global health. In both inflammatory and autoimmune diseases, dysregulated immune reactions mediated by tissue-residing immune and non-immune cells precipitate chronic inflammation and tissue damage that is amplified by peripheral immune cell extravasation into the tissue. Chemokine receptors are pivotal in orchestrating immune cell migration, yet deciphering the signaling code across cell types, diseases and tissues remains an open challenge. To delineate disease-specific cell-cell communications involved in immune cell migration, we conducted a meta-analysis of publicly available single-cell RNA sequencing (scRNA-seq) data across diverse immune diseases and tissues. Our comprehensive analysis spanned multiple immune disorders affecting major organs: atopic dermatitis and psoriasis (skin), chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis (lung), ulcerative colitis (colon), IgA nephropathy and lupus nephritis (kidney). By interrogating ligand-receptor (L-R) interactions, alterations in cell proportions, and differential gene expression, we unveiled intricate disease-specific and common immune cell chemoattraction and extravasation patterns. Our findings delineate disease-specific L-R networks and shed light on shared immune responses across tissues and diseases. Insights gleaned from this analysis hold promise for the development of targeted therapeutics aimed at modulating immune cell migration to mitigate inflammation and tissue damage. This nuanced understanding of immune cell dynamics at the single-cell resolution opens avenues for precision medicine in immune disease management., Competing Interests: CONFLICT OF INTEREST The authors are or were employees of Sanofi US at the time of this work.

Shear stress generated by the flow of blood in the vasculature is a potent regulator of endothelial cell function and vascular structure. While vascular responses to flow are complex and context-dependent, endothelial cell signaling in response to shear stress induced by laminar flows is coordinated by the transcription factor KLF2. The flow-dependent expression of KLF2 in endothelial cells is associated with a quiescent, anti-inflammatory phenotype and has been well characterized in two-dimensional systems but has not been studied in three-dimensional in vitro systems. Here we develop engineered microvascular networks (MVNs) that incorporate a KLF2-based endothelial cell flow sensor within a microfluidic chip, apply continuous flow using an attached microfluidic pump, and study the effects of this flow on vascular structure and function. We found that application of flow to MVNs for 48 h resulted in increased expression of the KLF2 reporter, larger vessel diameters, and decreased vascular branching and resistance. Notably, vessel diameters after the application of flow were independent of initial MVN morphologies. Finally, we found that MVNs exposed to flow have improved vascular barrier function and decreased platelet adhesion. MVNs with KLF2-based flow sensors represent a novel, powerful tool for evaluating the structural and functional effects of flow on engineered three-dimensional vascular systems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Cardiovascular disease plays a central role in the electrical and structural remodeling of the right atrium, predisposing to arrhythmias, heart failure, and sudden death. Here, we dissect with single-nuclei RNA sequencing (snRNA-seq) and spatial transcriptomics the gene expression changes in the human ex vivo right atrial tissue and pericardial fluid in ischemic heart disease, myocardial infarction, and ischemic and non-ischemic heart failure using asymptomatic patients with valvular disease who undergo preventive surgery as the control group. We reveal substantial differences in disease-associated gene expression in all cell types, collectively suggesting inflammatory microvascular dysfunction and changes in the right atrial tissue composition as the valvular and vascular diseases progress into heart failure. The data collectively suggest that investigation of human cardiovascular disease should expand to all functionally important parts of the heart, which may help us to identify mechanisms promoting more severe types of the disease., Competing Interests: Declaration of interests Authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Endocardial fibroelastosis (EFE) is defined by fibrotic tissue on the endocardium and forms partly through aberrant endothelial-to-mesenchymal transition. However, the pathologic triggers are still unknown. In this study, we showed that abnormal flow induces EFE partly through endothelial-to-mesenchymal transition in a rodent model, and that losartan can abrogate EFE development. Furthermore, we translated our findings to human endocardial endothelial cells, and showed that laminar flow promotes the suppression of genes associated with mesenchymal differentiation. These findings emphasize the role of flow in promoting EFE in endocardial endothelial cells and provide a novel potential therapy to treat this highly morbid condition., Competing Interests: This work has been supported by Boston Children’s Hospital, Department of Cardiovascular Surgery, Internal Funding Boston Children’s Hospital, Kaplan Fellowship. The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (© 2021 The Authors.)

Background: Plasmodium falciparum transmission depends on mature gametocytes that can be ingested by mosquitoes taking a blood meal on human skin. Although gametocyte skin sequestration has long been hypothesized as important contributor to efficient malaria transmission, this has never been formally tested., Methods: In naturally infected gametocyte carriers from Burkina Faso, we assessed infectivity to mosquitoes by direct skin feeding and membrane feeding. We directly quantified male and female gametocytes and asexual parasites in finger-prick and venous blood samples, skin biopsy samples, and in of mosquitoes that fed on venous blood or directly on skin. Gametocytes were visualized in skin tissue with confocal microscopy., Results: Although more mosquitoes became infected when feeding directly on skin then when feeding on venous blood (odds ratio, 2.01; 95% confidence interval, 1.21-3.33; P = .007), concentrations of gametocytes were not higher in the subdermal skin vasculature than in other blood compartments; only sparse gametocytes were observed in skin tissue., Discussion: Our data strongly suggest that there is no significant skin sequestration of P. falciparum gametocytes. Gametocyte densities in peripheral blood are thus informative for predicting onward transmission potential to mosquitoes and can be used to target and monitor malaria elimination initiatives., (© The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America.)

Background: A very large biomass of intact asexual-stage malaria parasites accumulates in the spleen of asymptomatic human individuals infected with Plasmodium vivax. The mechanisms underlying this intense tropism are not clear. We hypothesised that immature reticulocytes, in which P. vivax develops, may display high densities in the spleen, thereby providing a niche for parasite survival., Methods and Findings: We examined spleen tissue in 22 mostly untreated individuals naturally exposed to P. vivax and Plasmodium falciparum undergoing splenectomy for any clinical indication in malaria-endemic Papua, Indonesia (2015 to 2017). Infection, parasite and immature reticulocyte density, and splenic distribution were analysed by optical microscopy, flow cytometry, and molecular assays. Nine non-endemic control spleens from individuals undergoing spleno-pancreatectomy in France (2017 to 2020) were also examined for reticulocyte densities. There were no exclusion criteria or sample size considerations in both patient cohorts for this demanding approach. In Indonesia, 95.5% (21/22) of splenectomy patients had asymptomatic splenic Plasmodium infection (7 P. vivax, 13 P. falciparum, and 1 mixed infection). Significant splenic accumulation of immature CD71 intermediate- and high-expressing reticulocytes was seen, with concentrations 11 times greater than in peripheral blood. Accordingly, in France, reticulocyte concentrations in the splenic effluent were higher than in peripheral blood. Greater rigidity of reticulocytes in splenic than in peripheral blood, and their higher densities in splenic cords both suggest a mechanical retention process. Asexual-stage P. vivax-infected erythrocytes of all developmental stages accumulated in the spleen, with non-phagocytosed parasite densities 3,590 times (IQR: 2,600 to 4,130) higher than in circulating blood, and median total splenic parasite loads 81 (IQR: 14 to 205) times greater, accounting for 98.7% (IQR: 95.1% to 98.9%) of the estimated total-body P. vivax biomass. More reticulocytes were in contact with sinus lumen endothelial cells in P. vivax- than in P. falciparum-infected spleens. Histological analyses revealed 96% of P. vivax rings/trophozoites and 46% of schizonts colocalised with 92% of immature reticulocytes in the cords and sinus lumens of the red pulp. Larger splenic cohort studies and similar investigations in untreated symptomatic malaria are warranted., Conclusions: Immature CD71+ reticulocytes and splenic P. vivax-infected erythrocytes of all asexual stages accumulate in the same splenic compartments, suggesting the existence of a cryptic endosplenic lifecycle in chronic P. vivax infection. Findings provide insight into P. vivax-specific adaptions that have evolved to maximise survival and replication in the spleen., Competing Interests: The authors have declared that no competing interests exist.

Circulating levels of the adipokine leptin are linked to neuropathology in experimental cerebral malaria (ECM), but its source and regulation mechanism remain unknown. Here, we show that sequestration of infected red blood cells (iRBCs) in white adipose tissue (WAT) microvasculature increased local vascular permeability and leptin production. Mice infected with parasite strains that fail to sequester in WAT displayed reduced leptin production and protection from ECM. WAT sequestration and leptin induction were lost in CD36KO mice; however, ECM susceptibility revealed sexual dimorphism. Adipocyte leptin was regulated by the mechanistic target of rapamycin complex 1 (mTORC1) and blocked by rapamycin. In humans, although Plasmodium falciparum infection did not increase circulating leptin levels, iRBC sequestration, tissue leptin production, and mTORC1 activity were positively correlated with CM in pediatric postmortem WAT. These data identify WAT sequestration as a trigger for leptin production with potential implications for pathogenesis of malaria infection, prognosis, and treatment., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Transmission of Plasmodium parasites to the mosquito requires the formation and development of gametocytes. Studies in infected humans have shown that only the most mature forms of Plasmodium falciparum gametocytes are present in circulation, whereas immature forms accumulate in the hematopoietic environment of the bone marrow. We used the rodent model Plasmodium berghei to study gametocyte behavior through time under physiological conditions. Intravital microscopy demonstrated preferential homing of early gametocyte forms across the intact vascular barrier of the bone marrow and the spleen early during infection and subsequent development in the extravascular environment. During the acute phase of infection, we observed vascular leakage resulting in further parasite accumulation in this environment. Mature gametocytes showed high deformability and were found entering and exiting the intact vascular barrier. We suggest that extravascular gametocyte localization and mobility are essential for gametocytogenesis and transmission of Plasmodium to the mosquito.

Plasmodium vivax causes heavy burdens of disease across malarious regions worldwide. Mature P. vivax asexual and transmissive gametocyte stages occur in the blood circulation, and it is often assumed that accumulation/sequestration in tissues is not an important phase in their development. Here, we present a systematic study of P. vivax stage distributions in infected tissues of nonhuman primate (NHP) malaria models as well as in blood from human infections. In a comparative analysis of the transcriptomes of P. vivax and Plasmodium falciparum blood-stage parasites, we found a conserved cascade of stage-specific gene expression despite the greatly different gametocyte maturity times of these two species. Using this knowledge, we validated a set of conserved asexual- and gametocyte-stage markers both by quantitative real-time PCR and by antibody assays of peripheral blood samples from infected patients and NHP ( Aotus sp.). Histological analyses of P. vivax parasites in organs of 13 infected NHP ( Aotus and Saimiri species) demonstrated a major fraction of immature gametocytes in the parenchyma of the bone marrow, while asexual schizont forms were enriched to a somewhat lesser extent in this region of the bone marrow as well as in sinusoids of the liver. These findings suggest that the bone marrow is an important reservoir for gametocyte development and proliferation of malaria parasites. IMPORTANCE Plasmodium vivax malaria continues to cause major public health burdens worldwide. Yet, significant knowledge gaps in the basic biology and epidemiology of P. vivax malaria remain, largely due to limited available tools for research and diagnostics. Here, we present a systematic examination of tissue sequestration during P. vivax infection. Studies of nonhuman primates and malaria patients revealed enrichment of developing sexual stages (gametocytes) and mature replicative stages (schizonts) in the bone marrow and liver, relative to those present in peripheral blood. Identification of the bone marrow as a major P. vivax tissue reservoir has important implications for parasite diagnosis and treatment., (Copyright © 2018 Obaldia et al.)

Understanding transmission biology at an individual level is a key component of intervention strategies that target the spread of malaria parasites from human to mosquito. Gametocytes are specialized sexual stages of the malaria parasite life cycle developed during evolution to achieve crucial steps in transmission. As sexual differentiation and transmission are tightly linked, a deeper understanding of molecular and cellular events defining this relationship is essential to combat malaria. Recent advances in the field are gradually revealing mechanisms underlying sexual commitment, gametocyte sequestration, and dynamics of transmissible stages; however, key questions on fundamental gametocyte biology still remain. Moreover, species-specific variation between Plasmodium falciparum and Plasmodium vivax transmission dynamics pose another significant challenge for worldwide malaria elimination efforts. Here, we review the biology of transmission stages, highlighting numerous factors influencing development and dynamics of gametocytes within the host and determinants of human infectiousness., (Copyright © 2017 Cold Spring Harbor Laboratory Press; all rights reserved.)

Antimalarial drugs have thus far been chiefly derived from two sources-natural products and synthetic drug-like compounds. Here we investigate whether antimalarial agents with novel mechanisms of action could be discovered using a diverse collection of synthetic compounds that have three-dimensional features reminiscent of natural products and are underrepresented in typical screening collections. We report the identification of such compounds with both previously reported and undescribed mechanisms of action, including a series of bicyclic azetidines that inhibit a new antimalarial target, phenylalanyl-tRNA synthetase. These molecules are curative in mice at a single, low dose and show activity against all parasite life stages in multiple in vivo efficacy models. Our findings identify bicyclic azetidines with the potential to both cure and prevent transmission of the disease as well as protect at-risk populations with a single oral dose, highlighting the strength of diversity-oriented synthesis in revealing promising therapeutic targets.

Artemisinin resistance is rapidly spreading in Southeast Asia. The efficacy of artemisinin-combination therapy (ACT) continues to be excellent across Africa. We performed parasite transcriptional profiling and genotyping on samples from an antimalarial treatment trial in Uganda. We used qRT-PCR and genotyping to characterize residual circulating parasite populations after treatment with either ACT or ACT-primaquine. Transcripts suggestive of circulating ring stage parasites were present after treatment at a prevalence of >25% until at least 14 days post initiation of treatment. Greater than 98% of all ring stage parasites were cleared within the first 3 days, but subsequently persisted at low concentrations until day 14 after treatment. Genotyping demonstrated a significant decrease in multiplicity of infection within the first 2 days in both ACT and ACT-primaquine arms. However, multiple clone infections persisted until day 14 post treatment. Our data suggest the presence of genetically diverse persisting parasite populations after ACT treatment. Although we did not demonstrate clinical treatment failures after ACT and the viability and transmissibility of persisting ring stage parasites remain to be shown, these findings are of relevance for the interpretation of parasite clearance transmission dynamics and for monitoring drug effects in Plasmodium falciparum parasites.

Malaria parasites replicating inside red blood cells (RBCs) export a large subset of proteins into the erythrocyte cytoplasm to facilitate parasite growth and survival. PTEX, the parasite-encoded translocon, mediates protein transport across the parasitophorous vacuolar membrane (PVM) in Plasmodium falciparum-infected erythrocytes. Proteins exported into the erythrocyte cytoplasm have been localized to membranous structures, such as Maurer's clefts, small vesicles, and a tubovesicular network. Comparable studies of protein trafficking in Plasmodium vivax-infected reticulocytes are limited. With Plasmodium yoelii-infected reticulocytes, we identified exported protein 2 (Exp2) in a proteomic screen of proteins putatively transported across the PVM. Immunofluorescence studies showed that P. yoelii Exp2 (PyExp2) was primarily localized to the PVM. Unexpectedly, PyExp2 was also associated with distinct, membrane-bound vesicles in the reticulocyte cytoplasm. This is in contrast to P. falciparum in mature RBCs, where P. falciparum Exp2 (PfExp2) is exclusively localized to the PVM. Two P. yoelii-exported proteins, PY04481 (encoded by a pyst-a gene) and PY06203 (PypAg-1), partially colocalized with these PyExp2-positive vesicles. Further analysis revealed that with P. yoelii, Plasmodium berghei, and P. falciparum, cytoplasmic Exp2-positive vesicles were primarily observed in CD71(+) reticulocytes versus mature RBCs. In transgenic P. yoelii 17X parasites, the association of hemagglutinin-tagged PyExp2 with the PVM and cytoplasmic vesicles was retained, but the pyexp2 gene was refractory to deletion. These data suggest that the localization of Exp2 in mouse and human RBCs can be influenced by the host cell environment. Exp2 may function at multiple points in the pathway by which parasites traffic proteins into and through the reticulocyte cytoplasm., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)