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Objective: Aortic macrophage accumulation is characteristic of the pathogenesis of abdominal aortic aneurysm (AAA) but the mechanisms of macrophage accumulation and their phenotype are poorly understood. Lymphatic vessel endothelial receptor-1 (Lyve-1+) resident aortic macrophages independently self-renew and are functionally distinct from monocyte-derived macrophages recruited during inflammation. We hypothesized that Lyve-1+ and Lyve-1− macrophages differentially contribute to aortic aneurysm. Approach and results: Angiotensin-2 and β-aminopropionitrile (AT2/BAPN) were administered to induce AAA in C57BL/6J mice. Using immunohistochemistry (IHC), we demonstrated primarily adventitial accumulation of aortic macrophages, and in association with areas of elastin fragmentation and aortic dissection. Compared with controls, AAA was associated with a relative percent depletion of Lyve-1+ resident aortic macrophages and accumulation of Lyve-1− macrophages. Using CD45.1/CD45.2 parabiosis, we demonstrated aortic macrophage recruitment in AAA. Depletion of aortic macrophages in CCR2−/− mice was associated with reduced aortic dilatation indicating the functional role of recruitment from the bone marrow. Depletion of aortic macrophages using anti-macrophage colony-stimulating factor 1 receptor (MCSF1R)-neutralizing antibody (Ab) reduced the incidence of AAA. Conditional depletion of Lyve-1+ aortic macrophages was achieved by generating Lyve-1wt/cre Csf1rfl/fl mice. Selective depletion of Lyve-1+ aortic macrophages had no protective effects following AT2/BAPN administration and resulted in increased aortic dilatation in the suprarenal aorta. Conclusions: Aortic macrophage accumulation in AAA derives from adventitial recruitment of Lyve-1− macrophages, with relative percent depletion of Lyve-1+ macrophages. Selective targeting of macrophage subtypes represents a potential novel therapeutic avenue for the medical treatment of AAA.

The proto-oncogene c-myb (and corresponding nuclear transcription factor, c-Myb) regulates the proliferation and differentiation of hematologic and vascular smooth muscle cells; however, the role of c-Myb in blood pressure regulation is unknown. Here, we show that mice homozygous for a hypomorphic c-myb allele ( c-myb h/h ) conferring reduced c-Myb activity manifest reduced peripheral blood and kidney B220 + B-cells and have decreased systolic (104±2 versus 120±1 mm Hg; P P WT (wild type) mice. Additionally, c-myb h/h mice had lower susceptibility to deoxycorticosterone acetate-salt experimental hypertension. Although cardiac (echocardiography) and resistance artery (perfusion myography) functions were normal, metabolic cage studies revealed that c-myb h/h mice had increased 24-hour urine output and sodium excretion versus WT . Reconstitution of WT mice with c-myb h/h bone marrow transplant and chimeric bone marrow transplant using mice lacking B-cells ( J H T ; h/h>WT and h/h:J H T>WT , respectively) decreased blood pressure and increased 24-hour urine output compared with controls ( WT>WT ; WT:J H T>WT ). J H T mice also had decreased systolic (103±2 versus 115±1 mm Hg; P P WT . Real-time quantitative reverse transcription polymerase chain reaction of kidney medulla revealed reduced V 2 R (vasopressin receptor 2) expression in c-myb h/h and J H T mice. These data implicate B-cells in the regulation of V 2 R and its associated effects on salt and water handling and blood pressure homeostasis.

Inflammation is a key contributor to atherosclerosis with macrophages playing a pivotal role through the induction of oxidative stress and cytokine/chemokine secretion. DJ1, an anti-oxidant protein, has shown to paradoxically protect against chronic and acute inflammation. However, the role of DJ1 in atherosclerosis remains elusive. To assess the role of Dj1 in atherogenesis, we generated whole-body Dj1-deficient atherosclerosis-prone Apoe null mice (Dj1−/−Apoe−/−). After 21 weeks of atherogenic diet, Dj1−/− Apoe−/−mice were protected against atherosclerosis with significantly reduced plaque macrophage content. To assess whether haematopoietic or parenchymal Dj1 contributed to atheroprotection in Dj1-deficient mice, we performed bone-marrow (BM) transplantation and show that Dj1-deficient BM contributed to their attenuation in atherosclerosis. To assess cell-autonomous role of macrophage Dj1 in atheroprotection, BM-derived macrophages from Dj1-deficient mice and Dj1-silenced macrophages were assessed in response to oxidized low-density lipoprotein (oxLDL). In both cases, there was an enhanced anti-inflammatory response which may have contributed to atheroprotection in Dj1-deficient mice. There was also an increased trend of plasma DJ-1 levels from individuals with ischemic heart disease compared to those without. Our findings indicate an atheropromoting role of Dj1 and suggests that targeting Dj1 may provide a novel therapeutic avenue for atherosclerosis treatment or prevention.

Macrophages promote both injury and repair after myocardial infarction, but discriminating functions within mixed populations remains challenging. Here we used fate mapping, parabiosis and single-cell transcriptomics to demonstrate that at steady state, TIMD4+LYVE1+MHC-IIloCCR2− resident cardiac macrophages self-renew with negligible blood monocyte input. Monocytes partially replaced resident TIMD4–LYVE1–MHC-IIhiCCR2− macrophages and fully replaced TIMD4−LYVE1−MHC-IIhiCCR2+ macrophages, revealing a hierarchy of monocyte contribution to functionally distinct macrophage subsets. Ischemic injury reduced TIMD4+ and TIMD4– resident macrophage abundance, whereas CCR2+ monocyte-derived macrophages adopted multiple cell fates within infarcted tissue, including those nearly indistinguishable from resident macrophages. Recruited macrophages did not express TIMD4, highlighting the ability of TIMD4 to track a subset of resident macrophages in the absence of fate mapping. Despite this similarity, inducible depletion of resident macrophages using a Cx3cr1-based system led to impaired cardiac function and promoted adverse remodeling primarily within the peri-infarct zone, revealing a nonredundant, cardioprotective role of resident cardiac macrophages. Epelman and colleagues use fate mapping and single-cell transcriptomics to describe the dynamics of resident and recruited cardiac macrophages during ischemic injury.

Sca-1+ progenitor cells in the adult mouse aorta are known to generate vascular smooth muscle cells (VSMCs), but their embryological origins and temporal abundance are not known. Using tamoxifen-inducible Myf5-CreER mice, we demonstrate that Sca-1+ adult aortic cells arise from the somitic mesoderm beginning at E8.5 and continue throughout somitogenesis. Myf5 lineage-derived Sca-1+ cells greatly expand in situ, starting at 4 weeks of age, and become a major source of aortic Sca-1+ cells by 6 weeks of age. Myf5-derived adult aortic cells are capable of forming multicellular sphere-like structures in vitro and express the pluripotency marker Sox2. Exposure to transforming growth factor-β3 induces these spheres to differentiate into calponin-expressing VSMCs. Pulse-chase experiments using tamoxifen-inducible Sox2-CreERT2 mice at 8 weeks of age demonstrate that ∼35% of all adult aortic Sca-1+ cells are derived from Sox2+ cells. The present study demonstrates that aortic Sca-1+ progenitor cells are derived from the somitic mesoderm formed at the earliest stages of somitogenesis and from Sox2-expressing progenitors in adult mice.

Rationale: Inflammation is a key contributor to atherosclerosis. MicroRNA-146a (miR-146a) has been identified as a critical brake on proinflammatory nuclear factor κ light chain enhancer of activated B cells signaling in several cell types, including endothelial cells and bone marrow (BM)–derived cells. Importantly, miR-146a expression is elevated in human atherosclerotic plaques, and polymorphisms in the miR-146a precursor have been associated with risk of coronary artery disease. Objective: To define the role of endogenous miR-146a during atherogenesis. Methods and Results: Paradoxically, Ldlr −/− (low-density lipoprotein receptor null) mice deficient in miR-146a develop less atherosclerosis, despite having highly elevated levels of circulating proinflammatory cytokines. In contrast, cytokine levels are normalized in Ldlr −/− ;miR-146a −/− mice receiving wild-type BM transplantation, and these mice have enhanced endothelial cell activation and elevated atherosclerotic plaque burden compared with Ldlr −/− mice receiving wild-type BM, demonstrating the atheroprotective role of miR-146a in the endothelium. We find that deficiency of miR-146a in BM-derived cells precipitates defects in hematopoietic stem cell function, contributing to extramedullary hematopoiesis, splenomegaly, BM failure, and decreased levels of circulating proatherogenic cells in mice fed an atherogenic diet. These hematopoietic phenotypes seem to be driven by unrestrained inflammatory signaling that leads to the expansion and eventual exhaustion of hematopoietic cells, and this occurs in the face of lower levels of circulating low-density lipoprotein cholesterol in mice lacking miR-146a in BM-derived cells. Furthermore, we identify sortilin-1( Sort1 ), a known regulator of circulating low-density lipoprotein levels in humans, as a novel target of miR-146a. Conclusions: Our study reveals that miR-146a regulates cholesterol metabolism and tempers chronic inflammatory responses to atherogenic diet by restraining proinflammatory signaling in endothelial cells and BM-derived cells.

During obesity, macrophages can infiltrate metabolic tissues, and contribute to chronic low-grade inflammation, and mediate insulin resistance and diabetes. Recent studies have elucidated the metabolic role of JAK2, a key mediator downstream of various cytokines and growth factors. Our study addresses the essential role of macrophage JAK2 in the pathogenesis to obesity-associated inflammation and insulin resistance. During high-fat diet (HFD) feeding, macrophage-specific JAK2 knockout (M-JAK2−/−) mice gained less body weight compared to wildtype littermate control (M-JAK2+/+) mice and were protected from HFD-induced systemic insulin resistance. Histological analysis revealed smaller adipocytes and qPCR analysis showed upregulated expression of some adipogenesis markers in visceral adipose tissue (VAT) of HFD-fed M-JAK2−/− mice. There were decreased crown-like structures in VAT along with reduced mRNA expression of some macrophage markers and chemokines in liver and VAT of HFD-fed M-JAK2−/− mice. Peritoneal macrophages from M-JAK2−/− mice and Jak2 knockdown in macrophage cell line RAW 264.7 also showed lower levels of chemokine expression and reduced phosphorylated STAT3. However, leptin-dependent effects on augmenting chemokine expression in RAW 264.7 cells did not require JAK2. Collectively, our findings show that macrophage JAK2 deficiency improves systemic insulin sensitivity and reduces inflammation in VAT and liver in response to metabolic stress.

Immediate graft performance after lung transplantation is associated with short- and long-term clinical outcomes. However, the biologic mechanism that determines outcomes is not fully understood.To investigate the impact of cell death signals at 24 and 48 hours after lung transplantation on short- and long-term clinical outcomes.Plasma samples were collected pretransplantation and at 24 and 48 hours after transplant from 60 bilateral lung transplant recipients. Ten patients had primary graft dysfunction (PGD) grade 3 (PaO2/FiO2 ratio200 or on extracorporeal membrane oxygenation support) at 72 hours after transplant (PGD group). The remaining 50 patients were defined as the control group. Levels of plasma M30 (signifying epithelial apoptosis), M65 (signifying epithelial apoptosis plus necrosis), and high-mobility group box 1 protein (HMGB-1; signifying necrosis of all cell types) were measured by ELISA and correlated with clinical outcomes. Survival analyses were performed using Kaplan-Meier curves and Cox proportional hazards regression. Prediction accuracy of markers was assessed by calculated area under the curve of receiver operating characteristic graph.The PGD group had significantly higher M30 and M65 levels at 24 and 48 hours after transplant compared with the control group. There was no significant difference in HMGB-1. Area under the curve for 1-year survival was 0.86, 0.93, and 0.51 for M30, M65, and HMGB-1 at 48 hours, respectively. Survival analysis showed that higher M30 and M65 levels at 24 and 48 hours were significantly associated with worse survival. M65 at 48 hours remained significant even after adjustment for PGD. HMGB-1 was not significantly associated with survival.Recipient plasma concentration of epithelial cell death markers (M30, M65) after lung transplantation is negatively correlated with early graft performance and long-term survival.

Objective— Vascular smooth muscle cells (VSMCs) are believed to dedifferentiate and proliferate in response to vessel injury. Recently, adventitial progenitor cells were implicated as a source of VSMCs involved in vessel remodeling. c-Myb is a transcription factor known to regulate VSMC proliferation in vivo and differentiation of VSMCs from mouse embryonic stem cell–derived progenitors in vitro. However, the role of c-Myb in regulating specific adult vascular progenitor cell populations was not known. Our objective was to examine the role of c-Myb in the proliferation and differentiation of Sca1 + adventitial VSMC progenitor cells. Approach and Results— Using mice with wild-type or hypomorphic c-myb ( c-myb h/h ), BrdU (bromodeoxyuridine) uptake and flow cytometry revealed defective proliferation of Sca1 + adventitial VSMC progenitor cells at 8, 14, and 28 days post carotid artery denudation injury in c-myb h/h arteries. c-myb h/h cKit + CD34 − Flk1 − Sca1 + CD45 − Lin − cells failed to proliferate, suggesting that c-myb regulates the activation of specific Sca1 + progenitor cells in vivo and in vitro. Although expression levels of transforming growth factor-β1 did not vary between wild-type and c-myb h/h carotid arteries, in vitro differentiation of c-myb h/h Sca1 + cells manifested defective transforming growth factor-β1–induced VSMC differentiation. This is mediated by reduced transcriptional activation of myocardin because chromatin immunoprecipitation revealed c-Myb binding to the myocardin promoter only during differentiation of Sca1 + cells, myocardin promoter mutagenesis identified 2 specific c-Myb–responsive binding sites, and adenovirus-mediated expression of myocardin rescued the phenotype of c-myb h/h progenitors. Conclusions— These data support a role for c-Myb in the regulation of VSMC progenitor cells and provide novel insight into how c-myb regulates VSMC differentiation through myocardin.

Sca-1

Resident macrophages densely populate the normal arterial wall, yet their origins and the mechanisms that sustain them are poorly understood. Here we use gene-expression profiling to show that arterial macrophages constitute a distinct population among macrophages. Using multiple fate-mapping approaches, we show that arterial macrophages arise embryonically from CX3CR1(+) precursors and postnatally from bone marrow-derived monocytes that colonize the tissue immediately after birth. In adulthood, proliferation (rather than monocyte recruitment) sustains arterial macrophages in the steady state and after severe depletion following sepsis. After infection, arterial macrophages return rapidly to functional homeostasis. Finally, survival of resident arterial macrophages depends on a CX3CR1-CX3CL1 axis within the vascular niche.

Systemic inflammation perturbs the bone marrow environment by evicting resident B cells and favoring granulopoiesis over lymphopoiesis. Despite these conditions, a subset of marrow B cell remains to become activated and produce potent acute immunoglobulin M (IgM) responses. This discrepancy is currently unresolved and a complete characterization of early perturbations in the B-cell niche has not been undertaken. Here, we show that within a few hours of challenging mice with adjuvant or cecal puncture, B cells accumulate in the bone marrow redistributed away from sinusoid vessels. This response correlates with enhanced sensitivity to CXC chemokine ligand 12 (CXCL12) but not CXCL13 or CC chemokine ligand 21. Concurrently, a number of B-cell survival and differentiation factors are elevated to produce a transiently supportive milieu. Disrupting homing dynamics with a CXC chemokine receptor 4 inhibitor reduced the formation of IgM-secreting cells. These data highlight the rapidity with which peripheral inflammation modifies the marrow compartment, and demonstrate that such modifications regulate acute IgM production within this organ. Furthermore, our study indicates that conversion to a state of emergency granulopoiesis is temporally delayed, allowing B cells opportunity to respond to antigen.

A recent metaanalysis shows that 0.7% of nanoparticles are delivered to solid tumors. This low delivery efficiency has major implications in the translation of cancer nanomedicines, as most of the nanomedicines are sequestered by nontumor cells. To improve the delivery efficiency, there is a need to investigate the quantitative contribution of each organ in blocking the transport of nanoparticles to solid tumors. Here, we hypothesize that the removal of the liver macrophages, cells that have been reported to take up the largest amount of circulating nanoparticles, would lead to a significant increase in the nanoparticle delivery efficiency to solid tumors. We were surprised to discover that the maximum achievable delivery efficiency was only 2%. In our analysis, there was a clear correlation between particle design, chemical composition, macrophage depletion, tumor pathophysiology, and tumor delivery efficiency. In many cases, we observed an 18-150 times greater delivery efficiency, but we were not able to achieve a delivery efficiency higher than 2%. The results suggest the need to look deeper at other organs such as the spleen, lymph nodes, and tumor in mediating the delivery process. Systematically mapping the contribution of each organ quantitatively will allow us to pinpoint the cause of the low tumor delivery efficiency. This, in effect, enables the generation of a rational strategy to improve the delivery efficiency of nanoparticles to solid tumors either through the engineering of multifunctional nanosystems or through manipulation of biological barriers.

Artesunate remains the mainstay of treatment for cerebral malaria, but it is less effective in later stages of disease when the host inflammatory response and blood-brain barrier integrity dictate clinical outcomes. Nitric oxide (NO) is an important regulator of inflammation and microvascular integrity, and impaired NO bioactivity is associated with fatal outcomes in malaria. Endogenous NO bioactivity in mammals is largely mediated by S -nitrosothiols (SNOs). Based on these observations, we hypothesized that animals deficient in the SNO-metabolizing enzyme, S -nitrosoglutathione reductase (GSNOR), which exhibit enhanced S -nitrosylation, would have improved outcomes in a preclinical model of cerebral malaria. GSNOR knockout (KO) mice infected with Plasmodium berghei ANKA had significantly delayed mortality compared to WT animals ( P < 0.0001), despite higher parasite burdens ( P < 0.01), and displayed markedly enhanced survival versus the wild type (WT) when treated with the antimalarial drug artesunate (77% versus 38%; P < 0.001). Improved survival was associated with higher levels of protein-bound NO, decreased levels of CD4 + and CD8 + T cells in the brain, improved blood-brain barrier integrity, and improved coma scores, as well as higher levels of gamma interferon. GSNOR KO animals receiving WT bone marrow had significantly reduced survival following P. berghei ANKA infection compared to those receiving KO bone barrow ( P < 0.001). Reciprocal transplants established that survival benefits of GSNOR deletion were attributable primarily to the T cell compartment. These data indicate a role for GSNOR in the host response to malaria infection and suggest that strategies to disrupt its activity will improve clinical outcomes by enhancing microvascular integrity and modulating T cell tissue tropism.

Atherosclerosis is considered both a metabolic and inflammatory disease; however, the specific tissue and signaling molecules that instigate and propagate this disease remain unclear. The liver is a central site of inflammation and lipid metabolism that is critical for atherosclerosis, and JAK2 is a key mediator of inflammation and, more recently, of hepatic lipid metabolism. However, precise effects of hepatic Jak2 on atherosclerosis remain unknown. We show here that hepatic Jak2 deficiency in atherosclerosis-prone mouse models exhibited accelerated atherosclerosis with increased plaque macrophages and decreased plaque smooth muscle cell content. JAK2's essential role in growth hormone signalling in liver that resulted in reduced IGF-1 with hepatic Jak2 deficiency played a causal role in exacerbating atherosclerosis. As such, restoring IGF-1 either pharmacologically or genetically attenuated atherosclerotic burden. Together, our data show hepatic Jak2 to play a protective role in atherogenesis through actions mediated by circulating IGF-1 and, to our knowledge, provide a novel liver-centric mechanism in atheroprotection.

Summary: Mechanisms that govern transcriptional regulation of inflammation in atherosclerosis remain largely unknown. Here, we identify the nuclear transcription factor c-Myb as an important mediator of atherosclerotic disease in mice. Atherosclerosis-prone animals fed a diet high in cholesterol exhibit increased levels of c-Myb in the bone marrow. Use of mice that either harbor a c-Myb hypomorphic allele or where c-Myb has been preferentially deleted in B cell lineages revealed that c-Myb potentiates atherosclerosis directly through its effects on B lymphocytes. Reduced c-Myb activity prevents the expansion of atherogenic B2 cells yet associates with increased numbers of IgM-producing antibody-secreting cells (IgM-ASCs) and elevated levels of atheroprotective oxidized low-density lipoprotein (OxLDL)-specific IgM antibodies. Transcriptional profiling revealed that c-Myb has a limited effect on B cell function but is integral in maintaining B cell progenitor populations in the bone marrow. Thus, targeted disruption of c-Myb beneficially modulates the complex biology of B cells in cardiovascular disease. : Shikatani et al. demonstrate that the nuclear transcription factor c-Myb exacerbates experimental atherosclerosis directly through its effects on B lymphocytes. Paradoxically, c-Myb promotes B2 cell development yet limits numbers of IgM-producing antibody-secreting cells and levels of atheroprotective OxLDL-specific IgM antibodies.

In the version of this article initially published, the equal contribution of the third author was omitted. The footnote links for that author should be "Sara Nejat1,11" and the correct statement is as follows: "11These authors contributed equally: Sarah A. Dick, Jillian A. Macklin, Sara Nejat." The error has been corrected in the HTML and PDF versions of the article.

Prostate cancer (PCa) is the second most prevalent cancer in men after lung cancer. Prostate cancer develop- ment and progression is associated with the dysregulation of a number of molecular pathways; hence, therapeutic strate- gies targeting such pathways bring great promise. Recently we have shown that metformin, the anti-diabetic drug, can in- hibit tumor progression when combined with dutasteride, a 5-alpha-reductase inhibitor (5ARI). Interestingly, both met- formin and dutasteride have been reported to alter the Sterol Regulatory Element Binding Proteins (SREBP) Fatty Acid Synthase (FASN) pathway. The SREBP pathway is involved with lipid and energy homeostasis. In our present study, we investigated if dutasteride in combination with metformin can reduce the proliferation of LNCaP PCa cells, and whether this is mediated through the SREBP-1/FASN pathway. Human PCa cells were treated with either dutasteride (0-100 µM) or metformin (0-50 mM) alone or in combination. The treated cells were then incubated for up to 24 hours, and prolifera- tion assessed using the MTS 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazo- lium) assay. Western blot analysis was performed on cell lysates to assess alterations in key signaling molecules including cleaved SREBP-1, FASN, AR, PSA, pAMPK and apoptotic markers. Results revealed that there was a significant (p

Macrophages populate most tissues of the body. They perform many important functions that are required to maintain tissue homeostasis and fight infection, including the uptake and degradation of dead cells, debris, and foreign invaders. Macrophage ontogeny has been debated since the late 1960s when van Furth and Cohn1 postulated that macrophages are derived exclusively from bone marrow monocytes. However, the use of sophisticated in vivo fate-mapping approaches has recently shown that many tissue macrophages arise during embryogenesis in the yolk sac and fetal liver before the onset of definitive hematopoiesis.2–5 Two distinct developmental programs have been identified: early yolk sac–derived erythromyeloid progenitors that give rise to macrophages without monocyte intermediates and fetal liver monocytes that are derived from late c-Myb+ erythromyeloid progenitors generated in the yolk sac. In some circumstances, bone marrow–derived monocytes are also capable of colonizing developing tissues, especially during the perinatal period.6–9 The contributions of early and late erythromyeloid progenitors and hematopoietic stem cells to macrophage development vary considerably across different tissues.10 Article, see p 1498 In this issue of Circulation Research , Leid et al11 define macrophage ontogeny in the developing heart. At least 2 distinct populations of embryonic heart macrophages are identified based on the cell surface expression of the C-C chemokine receptor type 2 (CCR2), which encodes the receptor for monocyte chemoattractant protein-1. The authors previously demonstrated that CCR2 expression distinguished cardiac macrophages of adult monocyte versus embryonic origin.12 In the current study, genetic lineage tagging experiments using Csf1r MeriCreMer× Rosa26 Tomato mice administered tamoxifen at E7.5 (the approximate timing of yolk sac hematopoiesis) confirmed that primitive embryonic CCR2− heart macrophages are derived from the yolk sac. Complementary approaches using Rag1 Cre and Flt3 Cre mice further demonstrated that embryonic CCR2 …

Plasma cells (PC) are found in the CNS of multiple sclerosis (MS) patients, yet their source and role in MS remains unclear. We find that some PC in the CNS of mice with experimental autoimmune encephalomyelitis (EAE) originate in the gut and produce immunoglobulin A (IgA). Moreover, we show that IgA(+) PC are dramatically reduced in the gut during EAE, and likewise, a reduction in IgA-bound fecal bacteria is seen in MS patients during disease relapse. Removal of plasmablast (PB) and/or PC resulted in exacerbated EAE that was normalized by the introduction of gut-derived IgA(+) PC. Furthermore, mice with an over-abundance of IgA(+) PB and/or PC were specifically resistant to the effector stage of EAE, and expression of interleukin (IL)-10 by PB and/or PC was necessary and sufficient to confer resistance. Our data show that IgA(+) PB and/ or PC mobilized from the gut play an unexpected role in suppressing neuroinflammation.

Regions of the normal arterial intima predisposed to atherosclerosis are sites of ongoing monocyte trafficking and also contain resident myeloid cells with features of dendritic cells. However, the pathophysiological roles of these cells are poorly understood. Here we found that intimal myeloid cells underwent reverse transendothelial migration (RTM) into the arterial circulation after systemic stimulation of pattern-recognition receptors (PRRs). This process was dependent on expression of the chemokine receptor CCR7 and its ligand CCL19 by intimal myeloid cells. In mice infected with the intracellular pathogen Chlamydia muridarum, blood monocytes disseminated infection to the intima. Subsequent CCL19-CCR7-dependent RTM was critical for the clearance of intimal C. muridarum. This process was inhibited by hypercholesterolemia. Thus, RTM protects the normal arterial intima, and compromised RTM during atherogenesis might contribute to the intracellular retention of pathogens in atherosclerotic lesions.

Our understanding of vascular pathology relies on inducible animal models of disease that remain poorly described, and concern exists regarding indirect effects of the inducing agents. We sought to perform a detailed characterization of the immune response to a commonly used murine aneurysm model. Aneurysms were generated in 10 adult C57/Bl6 mice using 2 weeks of oral beta-amino propriono-nitrile (BAPN) administration and 4 weeks of angiotensin-2 (AT2) delivered via osmotic pump. FACS analysis was used to characterize progenitor and hematopoietic cell lines in bone marrow, blood and aorta. 3 mice died of aortic rupture between days 8 and 9. The remaining 7 were compared to age-matched controls. BAPN/AT2 treatment caused aortic dilatation at all aortic regions from the root to the descending thoracic aorta (P BAPN/AT2 induces aortic disease with aneurysmal degeneration of the suprarenal aorta. We observed a significant decrease in aortic macrophage proliferation suggestive of a mechanism of expansion independent of local macrophage proliferation. We did not observe a significant change in the bone marrow stem or progenitor cell compartment suggesting aortic injury is driving inflammation rather than direct stimulus of the marrow compartment by BAPN/AT2.

Summary The dogma that adaptive immunity is the only arm of the immune response with memory capacity has been recently challenged by several studies demonstrating evidence for memory-like innate immune training. However, the underlying mechanisms and location for generating such innate memory responses in vivo remain unknown. Here, we show that access of Bacillus Calmette–Guerin (BCG) to the bone marrow (BM) changes the transcriptional landscape of hematopoietic stem cells (HSCs) and multipotent progenitors (MPPs), leading to local cell expansion and enhanced myelopoiesis at the expense of lymphopoiesis. Importantly, BCG-educated HSCs generate epigenetically modified macrophages that provide significantly better protection against virulent M. tuberculosis infection than naive macrophages. By using parabiotic and chimeric mice, as well as adoptive transfer approaches, we demonstrate that training of the monocyte/macrophage lineage via BCG-induced HSC reprogramming is sustainable in vivo . Our results indicate that targeting the HSC compartment provides a novel approach for vaccine development.