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Macrophages are important players for the maintenance of tissue homeostasis(1). Perivascular and leptomeningeal macrophages reside in close proximity to the central nervous system (CNS) parenchyma(2), and their role in CNS physiology has not been well enough studied to date. Given their continuous interaction with the cerebrospinal fluid (CSF) and strategic positioning, we refer to these cells collectively as parenchymal border macrophages (PBMs). Here, we demonstrate that PBMs regulate CSF flow dynamics. We identify a subpopulation of PBMs expressing high levels of CD163 and Lyve1 (scavenger receptor proteins), located in close proximity to the brain arterial tree, and show that Lyve1+ PBMs regulate arterial motion that drives CSF flow. Pharmacological or genetic depletion of PBMs led to accumulation of extracellular matrix proteins, obstructing CSF access to perivascular spaces hence impairing CNS perfusion and clearance. Aging-associated alterations in PBMs and impairment of CSF dynamics were restored upon intracisternal injection of macrophage colony-stimulating growth factor (M-CSF). Human single-nuclei RNA sequencing data obtained from Alzheimer’s disease (AD) patients and healthy controls point to changes in phagocytosis/endocytosis and interferon-gamma (IFNγ) signaling on PBMs, pathways that are corroborated in a mouse AD model. Collectively, our results identify PBMs as novel cellular regulators of CSF flow dynamics, which could potentially be targeted pharmacologically to alleviate brain clearance deficits associated with aging and AD.

The recent revolution in tissue-resident macrophage biology has resulted largely from murine studies performed in C57BL/6 mice. Here, using both C57BL/6 and BALB/c mice, we analyze immune cells in the pleural cavity. Unlike C57BL/6 mice, naive tissue-resident large-cavity macrophages (LCMs) of BALB/c mice failed to fully implement the tissue-residency program. Following infection with a pleural-dwelling nematode, these pre-existing differences were accentuated with LCM expansion occurring in C57BL/6, but not in BALB/c mice. While infection drove monocyte recruitment in both strains, only in C57BL/6 mice were monocytes able to efficiently integrate into the resident pool. Monocyte-to-macrophage conversion required both T cells and interleukin-4 receptor alpha (IL-4Rα) signaling. The transition to tissue residency altered macrophage function, and GATA6+ tissue-resident macrophages were required for host resistance to nematode infection. Therefore, during tissue nematode infection, T helper 2 (Th2) cells control the differentiation pathway of resident macrophages, which determines infection outcome.

B cells, which are critical for intestinal homeostasis, remain understudied in ulcerative colitis (UC). In this study, we recruited three cohorts of patients with UC (primary cohort, n = 145; validation cohort 1, n = 664; and validation cohort 2, n = 143) to comprehensively define the landscape of B cells during UC-associated intestinal inflammation. Using single-cell RNA sequencing, single-cell IgH gene sequencing and protein-level validation, we mapped the compositional, transcriptional and clonotypic landscape of mucosal and circulating B cells. We found major perturbations within the mucosal B cell compartment, including an expansion of naive B cells and IgG(+) plasma cells with curtailed diversity and maturation. Furthermore, we isolated an auto-reactive plasma cell clone targeting integrin αvβ6 from inflamed UC intestines. We also identified a subset of intestinal CXCL13-expressing TFH-like T peripheral helper cells that were associated with the pathogenic B cell response. Finally, across all three cohorts, we confirmed that changes in intestinal humoral immunity are reflected in circulation by the expansion of gut-homing plasmablasts that correlates with disease activity and predicts disease complications. Our data demonstrate a highly dysregulated B cell response in UC and highlight a potential role of B cells in disease pathogenesis.

Targeting the α4β7-MAdCAM-1 axis with vedolizumab (VDZ) is a front-line therapeutic paradigm in ulcerative colitis (UC). However, mechanism(s) of action (MOA) of VDZ remain relatively undefined. Here, we examined three distinct cohorts of patients with UC (n=83, n=60, and n=21), to determine the effect of VDZ on the mucosal and peripheral immune system. Transcriptomic studies with protein level validation were used to study drug MOA using conventional and transgenic murine models. We found a significant decrease in colonic and ileal naïve B and T cells and circulating gut-homing plasmablasts (β7+) in VDZ-treated patients, pointing to gut-associated lymphoid tissue (GALT) targeting by VDZ. Murine Peyer’s patches (PP) demonstrated a significant loss cellularity associated with reduction in follicular B cells, including a unique population of epithelium-associated B cells, following anti-α4β7 antibody (mAb) administration. Photoconvertible (KikGR) mice unequivocally demonstrated impaired cellular entry into PPs in anti-α4β7 mAb treated mice. In VDZ-treated, but not anti-tumor necrosis factor-treated UC patients, lymphoid aggregate size was significantly reduced in treatment responders compared to non-responders, with an independent validation cohort further confirming these data. GALT targeting represents a novel MOA of α4β7-targeted therapies, with major implications for this therapeutic paradigm in UC, and for the development of new therapeutic strategies.

Intestinal failure-associated liver disease is a major morbidity associated with short bowel syndrome. We sought to determine if the obesity-resistant mouse strain (129S1/SvImJ) conferred protection from liver injury after small bowel resection (SBR). Using a parenteral nutrition-independent model of resection-associated liver injury, C57BL/6J and 129S1/SvImJ mice underwent a 50% proximal SBR or sham operation. At postoperative week 10, hepatic steatosis, fibrosis, and cholestasis were assessed. Hepatic and systemic inflammatory pathways were evaluated using oxidative markers and abundance of tissue macrophages. Potential mechanisms of endotoxin resistance were also explored. Serum lipid levels were elevated in all mouse lines. Hepatic triglyceride levels were no different between mouse strains, but there was an increased accumulation of free fatty acids in the C57BL/6J mice. Histological and serum markers of hepatic fibrosis, steatosis, and cholestasis were significantly elevated in resected C57BL/6J SBR mice as well as oxidative stress markers and macrophage recruitment in both the liver and visceral white fat in C57BL/6J mice compared with sham controls and the 129S1/SvImJ mouse line. Serum endotoxin levels were significantly elevated in C57BL/6J mice with significant elevation of hepatic TLR4 and reduction in PPARα expression levels. Despite high levels of serum lipids, 129S1/SvImJ mice did not develop liver inflammation, fibrosis, or cholestasis after SBR, unlike C57BL/6J mice. These data suggest that the accumulation of hepatic free fatty acids as well as increased endotoxin-driven inflammatory pathways through PPARα and TLR4 contribute to the liver injury seen in C57BL/6J mice with short bowel syndrome. NEW & NOTEWORTHY Unlike C57BL/6 mice, the 129S1/SvImJ strain is resistant to liver inflammation and injury after small bowel resection. These disparate outcomes are likely due to the accumulation of hepatic free fatty acids as well as increased endotoxin-driven inflammatory pathways through PPARα and TLR4 in C57BL/6 mice with short bowel syndrome.

Early atherosclerosis depends upon responses by immune cells resident in the intimal aortic wall. Specifically, the healthy intima is thought to be populated by vascular dendritic cells (DCs) that, during hypercholesterolemia, initiate atherosclerosis by being the first to accumulate cholesterol. Whether these cells remain key players in later stages of disease is unknown. Using murine lineage-tracing models and gene expression profiling, we reveal that myeloid cells present in the intima of the aortic arch are not DCs but instead specialized aortic intima resident macrophages (MacAIR) that depend upon colony-stimulating factor 1 and are sustained by local proliferation. Although MacAIR comprise the earliest foam cells in plaques, their proliferation during plaque progression is limited. After months of hypercholesterolemia, their presence in plaques is overtaken by recruited monocytes, which induce MacAIR-defining genes. These data redefine the lineage of intimal phagocytes and suggest that proliferation is insufficient to sustain generations of macrophages during plaque progression. Williams and colleagues investigate the origin, dynamics and transcriptional profiles of aortic intima macrophages during atherosclerosis disease progression.

Background The optimal regimen for enteral nutritional support in the management of children with short bowel syndrome (SBS) is not well characterized. A high fat, enteral diet is theoretically beneficial due to increased caloric density and enhanced structural adaptation. We therefore sought to determine the long-term effects of a high fat diet (HFD) on liver injury, a common complication of SBS, compared to a standard chow (SC) diet. Methods Using a parenteral nutrition-independent model of resection-associated liver injury, C57BL/6 mice underwent a sham operation or a 50% or 75% proximal small bowel resection (SBR). Mice in each group were then fed either a HFD (35% kcal fat) or SC (13% kcal fat). At post-operative week 15, markers of liver injury were quantified. Results Liver triglyceride levels were increased from 7- to 19-fold in mice on the HFD compared to mice fed SC in the sham, 50%, and 75% resection groups. Serum ALT (2.2-fold increase in 75% resected mice compared to sham controls) and AST (2.0- and 2.7-fold increases in 50% and 75% resected mice, respectively) levels as well as fibrotic liver staining were elevated only in resected mice fed a HFD. Conclusion Long-term enteral feeding of HFD in our murine SBS model is associated with hepatic steatosis and liver injury. Our observation that liver steatosis and injury occur independent of parenteral nutrition suggests that enteral feeding composition and magnitude of intestinal loss may make a significant contribution to intestinal failure-associated liver disease.

Key points Spontaneous contractions are essential for normal lymph transport and these contractions are exquisitely sensitive to the KATP channel activator pinacidil. KATP channel Kir6.1 and SUR2B subunits are expressed in mouse lymphatic smooth muscle (LSM) and form functional KATP channels as verified by electrophysiological techniques. Global deletion of Kir6.1 or SUR2 subunits results in severely impaired lymphatic contractile responses to pinacidil. Smooth muscle-specific expression of Kir6.1 gain-of-function mutant (GoF) subunits results in profound lymphatic contractile dysfunction and LSM hyperpolarization that is partially rescued by the KATP inhibitor glibenclamide. In contrast, lymphatic endothelial-specific expression of Kir6.1 GoF has essentially no effect on lymphatic contractile function. The high sensitivity of LSM to KATP channel GoF offers an explanation for the lymphoedema observed in patients with Cantu syndrome, a disorder caused by gain-of-function mutations in genes encoding Kir6.1 or SUR2, and suggests that glibenclamide may be an appropriate therapeutic agent. Abstract This study aimed to understand the functional expression of KATP channel subunits in distinct lymphatic cell types, and assess the consequences of altered KATP channel activity on lymphatic pump function. KATP channel subunits Kir6.1 and SUR2B were expressed in mouse lymphatic muscle by PCR, but only Kir6.1 was expressed in lymphatic endothelium. Spontaneous contractions of popliteal lymphatics from wild-type (WT) (C57BL/6J) mice, assessed by pressure myography, were very sensitive to inhibition by the SUR2-specific KATP channel activator pinacidil, which hyperpolarized both mouse and human lymphatic smooth muscle (LSM). In vessels from mice with deletion of Kir6.1 (Kir6.1-/- ) or SUR2 (SUR2[STOP]) subunits, contractile parameters were not significantly different from those of WT vessels, suggesting that basal KATP channel activity in LSM is not an essential component of the lymphatic pacemaker, and does not exert a strong influence over contractile strength. However, these vessels were >100-fold less sensitive than WT vessels to pinacidil. Smooth muscle-specific expression of a Kir6.1 gain-of-function (GoF) subunit resulted in severely impaired lymphatic contractions and hyperpolarized LSM. Membrane potential and contractile activity was partially restored by the KATP channel inhibitor glibenclamide. In contrast, lymphatic endothelium-specific expression of Kir6.1 GoF subunits had negligible effects on lymphatic contraction frequency or amplitude. Our results demonstrate a high sensitivity of lymphatic contractility to KATP channel activators through activation of Kir6.1/SUR2-dependent channels in LSM. In addition, they offer an explanation for the lymphoedema observed in patients with Cantu syndrome, a disorder caused by gain-of-function mutations in genes encoding Kir6.1/SUR2.

SummaryTissue-resident macrophages (TRMs) are long-lived cells that maintain locally and can be phenotypically distinct from monocyte-derived macrophages (MDMs). However, whether TRMs and MDMs have functional distinction under differing pathologies is not understood. Here, we show a significant portion of macrophages that accumulated during pancreatitis and pancreatic cancer were expanded from TRMs. We further established that pancreas TRMs have a distinct extracellular matrix remodeling phenotype that was critical for maintaining tissue homeostasis during inflammation. Loss of TRMs led to exacerbation of severe pancreatitis and animal death, due to impaired acinar cell survival and recovery. In pancreatitis, TRMs elicited protective effects by triggering the accumulation and activation of fibroblasts, which was necessary for initiating fibrosis as a wound healing response. The same TRM-driven fibrosis, however, drove pancreas cancer pathogenesis and progression. Together, these findings indicate that TRMs play divergent roles in the pathogenesis of pancreatitis and cancer through regulation of stromagenesis.

Recently, studies have emerged suggesting that the skin plays a role as major Na+ reservoir via regulation of the content of glycosaminoglycans and osmotic gradients. We investigated whether there were electrolyte gradients in skin and where Na+ could be stored to be inactivated from a fluid balance viewpoint. Na+ accumulation was induced in rats by a high salt diet (HSD) (8% NaCl and 1% saline to drink) or by implantation of a deoxycorticosterone acetate (DOCA) tablet (1% saline to drink) using rats on a low salt diet (LSD) (0.1% NaCl) on tap water as control. Na+ and K+ were assessed by ion chromatography in tissue eluates, and the extracellular volume by equilibration of 51Cr-EDTA. By tangential sectioning of the skin, we found a low Na+ content and extracellular volume in epidermis, both parameters rising by ∼30% and 100%, respectively, in LSD and even more in HSD and DOCA when entering dermis. We found evidence for an extracellular Na+ gradient from epidermis to dermis shown by an estimated concentration in epidermis ∼2 and 4–5 times that of dermis in HSD and DOCA-salt. There was intracellular storage of Na+ in skin, muscle, and myocardium without a concomitant increase in hydration. Our data suggest that there is a hydration-dependent high interstitial fluid Na+ concentration that will contribute to the skin barrier and thus be a mechanism for limiting water loss. Salt stress results in intracellular storage of Na+ in exchange with K+ in skeletal muscle and myocardium that may have electromechanical consequences. publishedVersion

Recently, studies have emerged suggesting that the skin plays a role as major Na

Barrier tissue immune responses are regulated, in part, by nociceptors. Nociceptor ablation alters local immune responses at peripheral sites and within draining lymph nodes (LNs). Nevertheless, the mechanisms and significance of nociceptor-dependent modulation of LN function are unknown. Using high-resolution imaging, viral tracing, single-cell transcriptomics, and optogenetics, we identified and functionally tested a sensory neuro-immune circuit that is responsive to lymph-borne inflammatory signals. Transcriptomic profiling revealed that multiple sensory neuron subsets – predominantly peptidergic nociceptors – innervate LNs, distinct from those innervating surrounding skin. To uncover LN-resident cells that may interact with LN-innervating sensory neurons, we generated a LN single-cell transcriptomic atlas and nominated nociceptor target populations and interaction modalities. Optogenetic stimulation of LN-innervating sensory fibers triggered rapid transcriptional changes within the predicted interacting cell types, particularly endothelium, stromal cells, and innate leukocytes. Thus, a unique population of sensory neurons monitors peripheral LNs and may locally regulate gene expression.

Two resident macrophage subsets reside in peritoneal fluid. Macrophages also reside within mesothelial membranes lining the peritoneal cavity, but they remain poorly characterized. Here, we identified two macrophage populations (LYVE1hi MHC IIlo-hi CX3CR1gfplo/− and LYVE1lo/− MHC IIhi CX3CR1gfphi subsets) in the mesenteric and parietal mesothelial linings of the peritoneum. These macrophages resembled LYVE1+ macrophages within surface membranes of numerous organs. Fate-mapping approaches and analysis of newborn mice showed that LYVE1hi macrophages predominantly originated from embryonic-derived progenitors and were controlled by CSF1 made by Wt1+ stromal cells. Their gene expression profile closely overlapped with ovarian tumor-associated macrophages previously described in the omentum. Indeed, syngeneic epithelial ovarian tumor growth was strongly reduced following in vivo ablation of LYVE1hi macrophages, including in mice that received omentectomy to dissociate the role from omental macrophages. These data reveal that the peritoneal compartment contains at least four resident macrophage populations and that LYVE1hi mesothelial macrophages drive tumor growth independently of the omentum.

Intestinal HDL is hepatoprotective High-density lipoprotein (HDL) is important for cholesterol metabolism and may have anti-inflammatory and antimicrobial properties. Although HDL is mainly produced by the liver, the intestine is also a source. Han et al. show in mice that intestinal HDL is not routed to the systemic circulation. Rather, in the form of HDL3, it is directly transported to the liver through the hepatic portal vein. There, it sequesters bacterial lipopolysaccharide from the gut that can trigger inflammation and liver damage. In various models of liver injury, loss of enteric HDL exacerbated pathology. By contrast, drugs elevating intestinal HDL improved disease outcomes. HDL3 is enriched in human portal venous blood, suggesting that enteric HDL may be targetable for the treatment of liver disease. Science , abe6729, this issue p. eabe6729

Disruption of lymphatic lipid transport is linked to obesity and type 2 diabetes (T2D), but regulation of lymphatic vessel function and its link to disease remain unclear. Here we show that intestinal lymphatic endothelial cells (LECs) have an increasing CD36 expression from lymphatic capillaries (lacteals) to collecting vessels, and that LEC CD36 regulates lymphatic integrity and optimizes lipid transport. Inducible deletion of CD36 in LECs in adult mice (Cd36ΔLEC) increases discontinuity of LEC VE-cadherin junctions in lacteals and collecting vessels. Cd36ΔLEC mice display slower transport of absorbed lipid, more permeable mesenteric lymphatics, accumulation of inflamed visceral fat and impaired glucose disposal. CD36 silencing in cultured LECs suppresses cell respiration, reduces VEGF-C-mediated VEGFR2/AKT phosphorylation and destabilizes VE-cadherin junctions. Thus, LEC CD36 optimizes lymphatic junctions and integrity of lymphatic lipid transport, and its loss in mice causes lymph leakage, visceral adiposity and glucose intolerance, phenotypes that increase risk of T2D., Genetic variants in CD36 have been associated with metabolic syndrome. Here, the authors found that lymphatic vessel integrity and lipid transport are influenced by CD36 expression, and lymphatic endothelial cell CD36 deficiency causes visceral obesity and insulin resistance, which are risk factors for metabolic syndrome and diabetes.

How the colon microenvironment confronts a breach of its epithelial border remains incompletely understood. In this issue, the laboratories of Lennon-Dumenil and Vignjevic reveal a novel role for macrophages in sustaining epithelial integrity in the face of fungal metabolites.

Significance A distinct murine model of multiple sclerosis used to examine factors involved in ectopic lymphoid tissue formation during central nervous system autoimmunity reveals that infiltration and aggregation of B cells within the leptomeninges is dependent upon B cell expression of VLA-4 and is preceded by neutrophil migration. This finding establishes the early mechanisms involved in the establishment of chronic inflammatory changes within the meninges during autoimmune inflammation that promote the formation of ectopic lymphoid tissue associated with disease progression and disability in multiple sclerosis., The success of B cell depletion therapies and identification of leptomeningeal ectopic lymphoid tissue (ELT) in patients with multiple sclerosis (MS) has renewed interest in the antibody-independent pathogenic functions of B cells during neuroinflammation. The timing and location of B cell antigen presentation during MS and its animal model experimental autoimmune encephalomyelitis (EAE) remain undefined. Using a new EAE system that incorporates temporal regulation of MHCII expression by myelin-specific B cells, we observed the rapid formation of large B cell clusters in the spinal cord subarachnoid space. Neutrophils preceded the accumulation of meningeal B cell clusters, and inhibition of CXCR2-mediated granulocyte trafficking to the central nervous system reduced pathogenic B cell clusters and disease severity. Further, B cell-restricted very late antigen-4 (VLA-4) deficiency abrogated EAE dependent on B cell antigen presentation. Together, our findings demonstrate that neutrophils coordinate VLA-4–dependent B cell accumulation within the meninges during neuroinflammation, a key early step in the formation of ELT observed in MS.

Most tissue-resident macrophage populations develop during embryogenesis, self-renew in the steady state and expand during type 2 immunity. Whether shared mechanisms regulate the proliferation of macrophages in homeostasis and disease is unclear. Here we found that the transcription factor Bhlhe40 was required in a cell-intrinsic manner for the self-renewal and maintenance of large peritoneal macrophages (LPMs), but not that of other tissue-resident macrophages. Bhlhe40 was necessary for the proliferation, but not the polarization, of LPMs in response to the cytokine IL-4. During infection with the helminth Heligmosomoides polygyrus bakeri, Bhlhe40 was required for cell cycling of LPMs. Bhlhe40 repressed the expression of genes encoding the transcription factors c-Maf and Mafb and directly promoted expression of transcripts encoding cell cycle-related proteins to enable the proliferation of LPMs. In LPMs, Bhlhe40 bound to genomic sites co-bound by the macrophage lineage-determining factor PU.1 and to unique sites, including Maf and loci encoding cell-cycle-related proteins. Our findings demonstrate a tissue-specific control mechanism that regulates the proliferation of resident macrophages in homeostasis and type 2 immunity. Edelson and colleagues show that the transcription factor Bhlhe40 is required in a cell-intrinsic manner for the self-renewal and maintenance of large peritoneal macrophages, but not that of other tissue-resident macrophages.

Clotting factors made by resident peritoneal macrophages promote microbial trapping in fluid microenvironments where microbes might otherwise escape., Macrophages resident in different organs express distinct genes, but understanding how this diversity fits into tissue-specific features is limited. Here, we show that selective expression of coagulation factor V (FV) by resident peritoneal macrophages in mice promotes bacterial clearance in the peritoneal cavity and serves to facilitate the well-known but poorly understood “macrophage disappearance reaction.” Intravital imaging revealed that resident macrophages were nonadherent in peritoneal fluid during homeostasis. Bacterial entry into the peritoneum acutely induced macrophage adherence and associated bacterial phagocytosis. However, optimal control of bacterial expansion in the peritoneum also required expression of FV by the macrophages to form local clots that effectively brought macrophages and bacteria in proximity and out of the fluid phase. Thus, acute cellular adhesion and resident macrophage–induced coagulation operate independently and cooperatively to meet the challenges of a unique, open tissue environment. These events collectively account for the macrophage disappearance reaction in the peritoneal cavity.

Arterial inflammation is a hallmark of atherosclerosis and appropriate management of this inflammation represents a major unmet therapeutic need for cardiovascular disease (CVD) patients. Here, we review the diverse contributions of immune cells to atherosclerosis, including mechanisms of activation in this context and the cytokine circuits that underlie disease progression, and the recent application of these insights in the form immunotherapy to treat cardiovascular disease. Recent studies on the cardiovascular comorbidity that arises in autoimmunity are revealing additional roles for cytokines in atherosclerosis. We discuss these findings and highlight data pointing to interleukin (IL)-1b, tumor necrosis factor, and IL-17 as cytokines that, at least in some settings, may present effective targets to reduce cardiovascular disease progression.

This cohort study investigates the association of sex hormones with disease severity and inflammatory cytokines in patients with COVID-19., Key Points Question Are circulating sex hormones associated with disease severity in patients with COVID-19? Findings In a cohort study of 152 patients with COVID-19, including 143 patients who were hospitalized, testosterone concentrations at presentation and on day 3 were inversely associated with disease severity and circulating inflammatory cytokine concentrations in men but not in women. Transcriptional profiling of circulating mononuclear cells revealed upregulation of hormone signaling pathways in patients requiring intensive care vs those with milder disease. Meaning These findings suggest that low testosterone concentrations may play a mechanistic role in worse outcomes observed in men with COVID-19, underscoring the need for clinical trials to test this hypothesis., Importance Male sex is a risk factor for developing severe COVID-19 illness. It is not known whether sex hormones contribute to this predisposition. Objective To investigate the association of concentrations of serum testosterone, estradiol, and insulinlike growth factor 1 (IGF-1, concentrations of which are regulated by sex hormone signaling) with COVID-19 severity. Design, Setting, and Participants This prospective cohort study was conducted using serum samples collected from consecutive patients who presented from March through May 2020 to the Barnes Jewish Hospital in St Louis, Missouri, with COVID-19 (diagnosed using nasopharyngeal swabs). Exposures Testosterone, estradiol, and IGF-1 concentrations were measured at the time of presentation (ie, day 0) and at days 3, 7, 14, and 28 after admission (if the patient remained hospitalized). Main Outcomes and Measures Baseline hormone concentrations were compared among patients who had severe COVID-19 vs those with milder COVID-19 illness. RNA sequencing was performed on circulating mononuclear cells to understand the mechanistic association of altered circulating hormone concentrations with cellular signaling pathways. Results Among 152 patients (90 [59.2%] men; 62 [40.8%] women; mean [SD] age, 63 [16] years), 143 patients (94.1%) were hospitalized. Among 66 men with severe COVID-19, median [interquartile range] testosterone concentrations were lower at day 0 (53 [18 to 114] ng/dL vs 151 [95 to 217] ng/dL; P = .01) and day 3 (19 [6 to 68] ng/dL vs 111 [49 to 274] ng/dL; P = .006) compared with 24 men with milder disease. Testosterone concentrations were inversely associated with concentrations of interleukin 6 (β = −0.43; 95% CI, −0.52 to −0.17; P

To coincide with JEM’s 125th anniversary, Randolph shared the story of Ralph Steinman's seminal work on dendritic cells., Ralph M. Steinman’s work on dendritic cells began in 1973 when he described and named the cells. Reminiscent of the late Justice Ginsburg’s perspective that enduring change happens not suddenly but one step at a time, the paper (1973. J. Exp. Med. https://doi.org/10.1084/jem.137.5.1142) was notably the first step in many steps of important work that revealed the nature of dendritic cells.

Tertiary lymphoid organs often arise during chronic inflammation, including in inflammatory bowel diseases like ileitis. The impact of TLOs on disease progression or immunity and how they integrate with or influence the surrounding tissue microenvironment remain unclear. In human Crohn's disease, we earlier observed that TLOs were positioned along mesenteric collecting lymphatic vessels (CLVs) that govern lymph outflow from the intestine. Here we show in the TNFΔARE mouse model of Crohn’s-like ileitis that TLOs form at valve regions of CLVs, supporting lymphangiogenic outgrowths. These TLOs compress CLVs, preventing forward lymph flow and immune cell egress to draining lymph nodes, while fostering lymph leak and backflow. Lymph transport through TLOs was restored if TNF neutralization was begun early. However, robustly developed TLOs resisted regression and restoration of flow. Thus, TLOs can profoundly remodel communication between tissues and their draining lymph nodes by strongly suppressing dissemination of cells and molecules.

Objective: vMIP-II (viral macrophage inflammatory protein 2)/vCCL2 (viral chemotactic cytokine ligand 2) binds to multiple chemokine receptors, and vMIP-II-based positron emission tomography tracer ( 64 Cu-DOTA-vMIP-II: vMIP-II tracer) accumulates at atherosclerotic lesions in mice. Given that it would be expected to react with multiple chemokine receptors on monocytes and macrophages, we wondered if its accumulation in atherosclerosis lesion-bearing mice might correlate with overall macrophage burden or, alternatively, the pace of monocyte recruitment. Approach and Results: We employed a mouse model of atherosclerosis regression involving adenoassociated virus 8 vector encoding murine Apoe (AAV-mApoE) treatment of Apoe −/− mice where the pace of monocyte recruitment slows before macrophage burden subsequently declines. Accumulation of 64 Cu-DOTA-vMIP-II at Apoe −/− plaque sites was strong but declined with AAV- mApoE -induced decline in monocyte recruitment, before macrophage burden reduced. Monocyte depletion indicated that monocytes and macrophages themselves were not the only target of the 64 Cu-DOTA-vMIP-II tracer. Using fluorescence-tagged vMIP-II tracer, competitive receptor blocking with CXCR4 antagonists, endothelial-specific Cre-mediated deletion of CXCR4, CXCR4-specific tracer 64 Cu-DOTA-FC131, and CXCR4 staining during disease progression and regression, we show endothelial cell expression of CXCR4 is a key target of 64 Cu-DOTA-vMIP-II imaging. Expression of CXCR4 was low in nonplaque areas but strongly detected on endothelium of progressing plaques, especially on proliferating endothelium, where vascular permeability was increased and monocyte recruitment was the strongest. Conclusions: Endothelial injury status of plaques is marked by CXCR4 expression and this injury correlates with the tendency of such plaques to recruit monocytes. Furthermore, our findings suggest positron emission tomography tracers that mark CXCR4 can be used translationally to monitor the state of plaque injury and monocyte recruitment.

Lymphatic vasculature is an integral part of digestive, immune and circulatory systems. The homeobox transcription factor PROX1 is necessary for the development of lymphatic vessels, lymphatic valves (LVs) and lymphovenous valves (LVVs). We and others previously reported a feedback loop between PROX1 and vascular endothelial growth factor-C (VEGF-C) signaling. PROX1 promotes the expression of the VEGF-C receptor VEGFR3 in lymphatic endothelial cells (LECs). In turn, VEGF-C signaling maintains PROX1 expression in LECs. However, the mechanisms of PROX1/VEGF-C feedback loop remain poorly understood. Whether VEGF-C signaling is necessary for LV and LVV development is also unknown. Here, we report for the first time that VEGF-C signaling is necessary for valve morphogenesis. We have also discovered that the transcriptional co-activators YAP and TAZ are required to maintain PROX1 expression in LVs and LVVs in response to VEGF-C signaling. Deletion of Yap and Taz in the lymphatic vasculature of mouse embryos did not affect the formation of LVs or LVVs, but resulted in the degeneration of these structures. Our results have identified VEGF-C, YAP and TAZ as a crucial molecular pathway in valve development., Summary: YAP and TAZ mediate the positive feedback loop between PROX1 and VEGF-C signaling in the developing lymphatic and lymphovenous valves.

Crohn’s disease [CD] is one of the two most common forms of inflammatory bowel disease, affecting over half a million Americans. Like many other diseases with chronic inflammation, some patients with CD develop tertiary lymphoid organs [TLO] in areas of the gastrointestinal tract with active disease. TLOs are organized clusters of lymphocytes, similar in structure to secondary lymphoid organs, though they develop after birth and their contribution to pathogenesis in CD, or other diseases, is unclear. We, and others, have also found B cell rich lymphoid aggregates in the mesenteric fat of CD patients along dramatically remodeled lymphatic vessels. TNFΔARE/+ is a murine model of ileal inflammation that recapitulates several key features of ileal CD, including development of mesenteric tertiary lymphoid organs. Use of this model revealed that mesenteric TLOs block cellular and molecular export from the gut, leading us to wonder if mechanisms that interfere with their development might reduce ileitis. TNFΔARE/+ mice that lack B cells revealed that B cells are required for tertiary lymphoid organ formation in this model. Without these TLOs, lymphatic outflow from the intestine was restored. Nonetheless, histological and flow cytometric approaches reveal no difference in local inflammation in the ileum. However, systemic inflammation, as assessed by metabolic cages and changes in body weight over time, increased. This suggests that TLOs may act to trap inflammatory signals locally, preventing systemic dissemination of inflammatory cells or mediators. Work supported by NIH grants DP1-DK109668-04 and T32-DK077653-27 and the Kenneth Rainin Foundation

Immunoglobulin A (IgA) secretion by plasma cells (PCs), terminally differentiated B cells residing in the intestinal lamina propria, assures microbiome homeostasis and protects the host against enteric infections. However, whether exposure to diet-derived and commensal-derived signals instruct tissue resident PCs effector function and dynamically shape IgA immune responses at the mucosal barrier remain largely uninvestigated. Here, we demonstrated that intestinal epithelial cells (IECs) integrate luminal input to produce 7α,25-dihydroxycholesterol (7α,25-HC), a cholesterol metabolite (oxysterol) with immunomodulatory functions. In IECs, both cholesterol uptake via NPC1L1 and commensal recognition via MyD88 controlled oxysterol production. Mice lacking the oxysterol enzyme CH25H specifically in IECs abolished 7α,25-HC production and allowed to study oxysterol generation and activity in the small intestine. Inability of IECs to generate 7α,25-HC enhanced IgA secretion by PCs in the gut, suggesting that oxysterol negatively regulate humoral response at the mucosal barriers. Mechanistically, we showed that intestinal PCs sensed 7α,25-HC via the chemoattractant receptor GPR183 to position in the lamina propria tissue. This IEC-PC axis was rapidly modulated by cholesterol dietary content and tuned Salmonella-specific IgA response. Our finding revealed a new mechanism linking dietary cholesterol and humoral immune responses centered around PC localization for efficient mucosal protection. Supported by grants from Kenneth Rainin Foundation, Innovator Award, Charles H. Hood Foundation Child Health Research Awards Program, The Leukemia and Lymphoma Society New Idea Award and the Multiple Myeloma Research Fellowship, NIH ( AI40098 ) and The American Association of Immunologists Careers in Immunology Fellowship Program.

Lymphatic collecting vessels and lymph nodes are inevitably embedded in adipose tissue. The physiological significance of this observation remains still not elucidated. However, obesity is characterized by impaired lymphatic function and increased vessel permeability. Inversely, lymphatic dysfunction induces obesity in mice, suggesting a significant interplay between lymphatic vessels and the adipose tissue. Therefore, understanding factors leading to lymphatic dysfunction might open new therapeutic windows to prevent obesity and associated comorbidities. The first step in this process requires a precise and detailed visualization of the lymphatic network in healthy and inflamed adipose tissue. Here, we describe a rapid, inexpensive, and efficient method that allows to label and analyze lymphatic and blood vessels. This approach takes advantage of the skin-draining brachial lymph node localization within the subcutaneous adipose tissue. The lymphatic arborization of this tissue can be revealed by injecting fluorochrome-conjugated lectins subcutaneously. Moreover, the in vivo labeling approach provides a way to evaluate lymphatic vessel density and functions. Coupled to blood vessel, adipocyte and immune cell staining, the protocol allows for high-resolution mapping of the subcutaneous adipose tissue by 3D imaging.

SummaryAssembly of high density lipoprotein (HDL) requires apoA1 and the cholesterol transporter ABCA1. Although the liver generates most HDL in blood, HDL synthesis also occurs in the small intestine. However, distinct functions for intestinal HDL are unknown. Here we show that HDL in the portal vein, which connects intestine to liver, derivesd mainly from intestine and potently neutralizes lipopolysaccharide (LPS). In a mouse model of short bowel syndrome where liver inflammation and fibrosis was driven by the LPS receptor TLR4, loss of intestine-derived HDL worsened liver injury, whereas liver status was improved by therapeutics that elevated and depended upon intestinal HDL production. Thus, protection of the liver from injury in response to gut-derived signals like LPS is a major function of intestinally synthesized HDL.

Cardiac myocytes have multiple cell autonomous mechanisms that facilitate stabilization and repair of damaged sarcolemmal membranes following myocardial injury. Dysferlin is a protein which facilitates membrane repair by promoting membrane resealing. Although prior studies have shown that dysferlin-deficient (Dysf−/−) mouse hearts have an impaired recovery from acute ischemia/reperfusion (I/R) injury ex vivo, the role of dysferlin in mediating the recovery from myocardial injury in vivo is unknown. Here we show that Dysf−/− mice develop adverse LV remodeling following I/R injury secondary to the collateral damage from sustained myocardial inflammation within the infarct zone. Backcrossing Dysf−/− mice with mice lacking signaling through the Toll-Interleukin 1 Receptor Domain-Containing Adaptor Protein (Tirap−/−), attenuated inflammation and abrogated adverse LV remodeling following I/R injury. Subsequent studies using Poloxamer 188 (P188), a membrane resealing reagent, demonstrated that P188 did not attenuate inflammation nor prevent adverse LV remodeling in Dysf−/− mice following I/R injury. Viewed together these studies reveal a previously unappreciated role for the importance of membrane sealing and the resolution of inflammation following myocardial injury.

We dissect metabolic variability of mononuclear phagocyte (MNP) subpopulations across different tissues through integrative analysis of three large scale datasets. Specifically, we introduce ImmGen MNP Open Source dataset that profiled 337 samples and extended previous ImmGen effort which included 202 samples of mononuclear phagocytes and their progenitors. Next, we analysed Tabula Muris Senis dataset to extract data for 51,364 myeloid cells from 18 tissues. Taken together, a compendium of data assembled in this work covers phagocytic populations found across 38 different tissues. To analyse common metabolic features, we developed novel network-based computational approach for unbiased identification of key metabolic subnetworks based on cellular transcriptional profiles in large-scale datasets. Using ImmGen MNP Open Source dataset as baseline, we define 9 metabolic subnetworks that encapsulate the metabolic differences within mononuclear phagocytes, and demonstrate that these features are robustly found across all three datasets, including lipid metabolism, cholesterol biosynthesis, glycolysis, and a set of fatty acid related metabolic pathways, as well as nucleotide and folate metabolism. We systematically define major features specific to macrophage and dendritic cell subpopulations. Among other things, we find that cholesterol synthesis appears particularly active within the migratory dendritic cells. We demonstrate that interference with this pathway through statins administration diminishes migratory capacity of the dendritic cells in vivo. This result demonstrates the power of our approach and highlights importance of metabolic diversity among mononuclear phagocytes.

Mammals have two specialized vascular circulatory systems, the blood vasculature and the lymphatic vasculature. The lymphatic vasculature provides a unidirectional conduit that returns filtered interstitial arterial fluid and tissue metabolites to the blood circulation. It also plays major roles in immune cell trafficking and lipid absorption. As we discuss in this review, the molecular characterization of lymphatic vascular development and our understanding of this vasculature’s role in pathophysiological conditions has greatly improved in recent years, changing conventional views about the roles of the lymphatic vasculature in health and disease. Morphological or functional defects in the lymphatic vasculature have now been uncovered in several pathological conditions. We propose that subtle, asymptomatic alterations in lymphatic vascular function could underlie the variability seen in the body’s response to a wide range of human diseases.

Viral macrophage inflammatory protein 2 (vMIP-II/vCCL2) binds to multiple chemokine receptors, and vMIP-II based PET tracer (64Cu-DOTA-vMIP-II: vMIP-II tracer) accumulates at atherosclerotic lesions in mice. The magnitude of 64Cu-DOTA-vMIP-II accumulation correlated with monocyte recruitment, as Apoe-/- mice treated with AAV-mApoE showed PET signal declining as monocyte recruitment subsided. Unexpectedly, monocytes themselves were not the major target of the 64Cu-DOTA-vMIP-II tracer. Using fluorescence-tagged vMIP-II tracer, competitive receptor blocking with CXCR4 antagonists, CXCR4-specific tracer 64Cu-DOTA-FC131, or CXCR4 staining during disease progression and regression, endothelial cell expression of CXCR4 proved to be the main target of 64Cu-DOTA-vMIP-II imaging. Expression of CXCR4 was low in non-plaque areas, but strongly detected on endothelium at the edges of progressing plaques, corresponding to a population of proliferating endothelium and to the location in plaques where monocyte recruitment occurred. Thus, endothelial injury status of plaques is marked by CXCR4 expression and that this injury correlates with the tendency of such plaques to recruit monocytes. Furthermore, our findings suggest PET tracers that, through binding CXCR4, may be useful to monitor plaque injury status.