Characterization of conventional and atypical receptors for the chemokine CCL2 on mouse leukocytes

Hypertrophic heart failure promotes gut dysbiosis and gut leakage in interleukin 10-deficient mice

Heart failure (HF) is a leading cause of death worldwide. We have shown that pressure overload (PO)-induced inflammatory cell recruitment leads to heart failure in IL-10 knockout (KO) mice. However, it is unclear whether PO-induced inflammatory cells also target the gut mucosa, causing gut dysbiosis and leakage. We hypothesized that transverse aortic constriction (TAC) exacerbates immune cell homing to the gut (small intestine and colon), promoting dysbiosis and gut leakage in IL-10 KO mice. HF was induced in 8- to 10-wk-old C57BL/6J wild-type (WT) and B6.129P2-Il10tm1Cgn/J mutant (IL-10 KO) male and female mice by TAC and cardiac function was measured using visual sonics VEVO 3100. Fourteen days post-TAC, levels of monocytes, macrophages, neutrophils, and proinflammatory cytokines were measured in blood and gut. Gut dysbiosis was assessed via 16S rRNA sequencing in feces at 56 days post-TAC. IL-10 KO mice showed worsened cardiac dysfunction post-TAC. TAC worsened monocytes, and neutrophils infiltration in systemic circulation and facilitated their homing to the gut in IL-10 KO mice. Intriguingly, proinflammatory cytokines level was increased in blood, and gut of IL-10 KO mice following TAC. Furthermore, IL-10 expression was reduced in the colon of WT mice post-TAC. Moreover, TAC exacerbated gut dysbiosis in IL-10 KO mice. Finally, an impaired intestinal permeability was noted in IL-10 KO mice post-TAC. In conclusion, TAC-induced systemic inflammation leads to gut dysbiosis and impaired gut permeability in IL-10 KO mice, indicating IL-10's potential role in regulating intestinal integrity and microbiota balance during heart failure.NEW & NOTEWORTHY IL-10, crucial for systemic inflammation regulation and gut mucosal homeostasis, was investigated using IL-10 knockout (KO) mice. Exacerbated gut inflammation was observed post-transverse aortic constriction (TAC) in IL-10-depleted mice, whereas wild-type (WT) mice showed reduced IL-10 gene expression in colon and ileum. TAC induced gut dysbiosis and leakage in IL-10 KO mice, suggesting a link between enhanced inflammatory signaling in heart failure and multi-organ damage via gut dysbiosis and leakage.

Atypical chemokine receptors in the immune system

Leukocyte migration is a fundamental component of innate and adaptive immune responses as it governs the recruitment and localization of these motile cells, which is crucial for immune cell priming, effector functions, memory responses and immune regulation. This complex cellular trafficking system is controlled to a large extent via highly regulated production of secreted chemokines and the restricted expression of their membrane-tethered G-protein-coupled receptors. The activity of chemokines and their receptors is also regulated by a subfamily of molecules known as atypical chemokine receptors (ACKRs), which are chemokine receptor-like molecules that do not couple to the classical signalling pathways that promote cell migration in response to chemokine ligation. There has been a great deal of progress in understanding the biology of these receptors and their functions in the immune system in the past decade. Here, we describe the contribution of the various ACKRs to innate and adaptive immune responses, focussing specifically on recent progress. This includes recent findings that have defined the role for ACKRs in sculpting extracellular chemokine gradients, findings that broaden the spectrum of chemokine ligands recognized by these receptors, candidate new additions to ACKR family, and our increasing understanding of the role of these receptors in shaping the migration of innate and adaptive immune cells.

The atypical chemokine receptor 2 reduces T cell expansion and tertiary lymphoid tissue but does not limit autoimmune organ injury in lupus-prone B6lpr mice

Introduction

The atypical chemokine receptor 2 (ACKR2) is a chemokine scavenger receptor, which limits inflammation and organ damage in several experimental disease models including kidney diseases. However, potential roles of ACKR2 in reducing inflammation and tissue injury in autoimmune disorders like systemic lupus erythematosus (SLE) and lupus nephritis are unknown, as well as its effects on systemic autoimmunity.

Methods

To characterize functional roles of ACKR2 in SLE, genetic Ackr2 deficiency was introduced into lupus-prone C57BL/6lpr (Ackr2-/- B6lpr) mice.

Results

Upon inflammatory stimulation in vitro, secreted chemokine levels increased in Ackr2 deficient tubulointerstitial tissue but not glomeruli. Moreover, Ackr2 expression was induced in kidneys and lungs of female C57BL/6lpr mice developing SLE. However, female Ackr2-/- B6lpr mice at 28 weeks of age showed similar renal functional parameters as wildtype (WT)-B6lpr mice. Consistently, assessment of activity and chronicity indices for lupus nephritis revealed comparable renal injury. Interestingly, Ackr2-/- B6lpr mice showed significantly increased renal infiltrates of CD3+ T and B cells, but not neutrophils, macrophages or dendritic cells, with T cells predominantly accumulating in the tubulointerstitial compartment of Ackr2-/- B6lpr mice. In addition, histology demonstrated significantly increased peribronchial lung infiltrates of CD3+ T cells in Ackr2-/- B6lpr mice. Despite this, protein levels of pro-inflammatory chemokines and mRNA expression of inflammatory mediators were not different in kidneys and lungs of WT- and Ackr2-/- B6lpr mice. This data suggests compensatory mechanisms for sufficient chemokine clearance in Ackr2-deficient B6lpr mice in vivo. Analysis of systemic autoimmune responses revealed comparable levels of circulating lupus-associated autoantibodies and glomerular immunoglobulin deposition in the two genotypes. Interestingly, similar to kidney and lung CD4+ T cell numbers and activation were significantly increased in spleens of Ackr2-deficient B6lpr mice. In lymph nodes of Ackr2-/- B6lpr mice abundance of activated dendritic cells decreased, but CD4+ T cell numbers were comparable to WT. Moreover, increased plasma levels of CCL2 were present in Ackr2-/- B6lpr mice, which may facilitate T cell mobilization into spleens and peripheral organs.

Discussion

In summary, we show that ACKR2 prevents expansion of T cells and formation of tertiary lymphoid tissue, but is not essential to limit autoimmune tissue injury in lupus-prone B6lpr mice.

CCL2-CCR2 signaling axis in obesity and metabolic diseases

Obesity and metabolic diseases, such as insulin resistance, type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular ailments, represent formidable global health challenges, bearing considerable implications for both morbidity and mortality rates. It has become increasingly evident that chronic, low-grade inflammation plays a pivotal role in the genesis and advancement of these conditions. The involvement of C-C chemokine ligand 2 (CCL2) and its corresponding receptor, C-C chemokine receptor 2 (CCR2), has been extensively documented in numerous inflammatory maladies. Recent evidence indicates that the CCL2/CCR2 pathway extends beyond immune cell recruitment and inflammation, exerting a notable influence on the genesis and progression of metabolic syndrome. The present review seeks to furnish a comprehensive exposition of the CCL2-CCR2 signaling axis within the context of obesity and metabolic disorders, elucidating its molecular mechanisms, functional roles, and therapeutic implications.

Cytomegalovirus and Cardiovascular Disease: A Hypothetical Role for Viral G-Protein-Coupled Receptors in Hypertension

Cytomegalovirus (CMV) is a member of the β-herpesviruses and is ubiquitous, infecting 50%-99% of the human population depending on ethnic and socioeconomic conditions. CMV establishes lifelong, latent infections in their host. Spontaneous reactivation of CMV is usually asymptomatic, but reactivation events in immunocompromised or immunosuppressed individuals can lead to severe morbidity and mortality. Moreover, herpesvirus infections have been associated with several cardiovascular and post-transplant diseases (stroke, atherosclerosis, post-transplant vasculopathy, and hypertension). Herpesviruses, including CMV, encode viral G-protein-coupled receptors (vGPCRs) that alter the host cell by hijacking signaling pathways that play important roles in the viral life cycle and these cardiovascular diseases. In this brief review, we discuss the pharmacology and signaling properties of these vGPCRs, and their contribution to hypertension. Overall, these vGPCRs can be considered attractive targets moving forward in the development of novel hypertensive therapies.

The dual-function chemokine receptor CCR2 drives migration and chemokine scavenging through distinct mechanisms

C-C chemokine receptor 2 (CCR2) is a dual-function receptor. Similar to other G protein-coupled chemokine receptors, it promotes monocyte infiltration into tissues in response to the chemokine CCL2, and, like atypical chemokine receptors (ACKRs), it scavenges chemokine from the extracellular environment. CCR2 therefore mediates CCL2-dependent signaling as a G protein-coupled receptor (GPCR) and also limits CCL2 signaling as a scavenger receptor. We investigated the mechanisms underlying CCR2 scavenging, including the involvement of intracellular proteins typically associated with GPCR signaling and internalization. Using CRISPR knockout cell lines, we showed that CCR2 scavenged by constitutively internalizing to remove CCL2 from the extracellular space and recycling back to the cell surface for further rounds of ligand sequestration. This process occurred independently of G proteins, GPCR kinases (GRKs), β-arrestins, and clathrin, which is distinct from other "professional" chemokine scavenger receptors that couple to GRKs, β-arrestins, or both. These findings set the stage for understanding the molecular regulators that determine CCR2 scavenging and may have implications for drug development targeting this therapeutically important receptor.

Role of the CCL2-CCR2 axis in cardiovascular disease: Pathogenesis and clinical implications

The CCL2-CCR2 axis is one of the major chemokine signaling pathways that has received special attention because of its function in the development and progression of cardiovascular disease. Numerous investigations have been performed over the past decades to explore the function of the CCL2-CCR2 signaling axis in cardiovascular disease. Laboratory data on the CCL2-CCR2 axis for cardiovascular disease have shown satisfactory outcomes, yet its clinical translation remains challenging. In this article, we describe the mechanisms of action of the CCL2-CCR2 axis in the development and evolution of cardiovascular diseases including heart failure, atherosclerosis and coronary atherosclerotic heart disease, hypertension and myocardial disease. Laboratory and clinical data on the use of the CCL2-CCR2 pathway as a targeted therapy for cardiovascular diseases are summarized. The potential of the CCL2-CCR2 axis in the treatment of cardiovascular diseases is explored.

Recruitment of dendritic cell progenitors to foci of influenza A virus infection sustains immunity

Protection from infection with respiratory viruses such as influenza A virus (IAV) requires T cell–mediated immune responses initiated by conventional dendritic cells (cDCs) that reside in the respiratory tract. Here, we show that effective induction of T cell responses against IAV in mice requires reinforcement of the resident lung cDC network by cDC progenitors. We found that CCR2-binding chemokines produced during IAV infection recruit pre-cDCs from blood and direct them to foci of infection, increasing the number of progeny cDCs next to sites of viral replication. Ablation of CCR2 in the cDC lineage prevented this increase and resulted in a deficit in IAV-specific T cell responses and diminished resistance to reinfection. These data suggest that the homeostatic network of cDCs in tissues is insufficient for immunity and reveal a chemokine-driven mechanism of expansion of lung cDC numbers that amplifies T cell responses against respiratory viruses.

Marginal Zone Formation Requires ACKR3 Expression on B Cells

The marginal zone (MZ) contributes to the highly organized spleen microarchitecture. We show that expression of atypical chemokine receptor 3 (ACKR3) defines two equal-sized populations of mouse MZ B cells (MZBs). ACKR3 is required for development of a functional MZ and for positioning of MZBs. Deletion of ACKR3 on B cells distorts the MZ, and MZBs fail to deliver antigens to follicles, reducing humoral responses. Reconstitution of MZ-deficient CD19^ko mice shows that ACKR3^- MZBs can differentiate into ACKR3⁺ MZBs, but not vice versa. The lack of a MZ is rescued by adoptive transfer of ACKR3-sufficient, and less by ACKR3-deficient, follicular B cells (FoBs); hence, ACKR3 expression is crucial for establishment of the MZ. The inability of CD19^ko mice to respond to T-independent antigen is rescued when ACKR3-proficient, but not ACKR3-deficient, FoBs are transferred. Accordingly, ACKR3-deficient FoBs are able to reconstitute the MZ if the niche is pre-established by ACKR3-proficient MZBs.

A Versatile Toolkit for Semi-Automated Production of Fluorescent Chemokines to Study CCR7 Expression and Functions

Chemokines guide leukocyte migration in different contexts, including homeostasis, immune surveillance and immunity. The chemokines CCL19 and CCL21 control lymphocyte and dendritic cell migration and homing to lymphoid organs. Thereby they orchestrate adaptive immunity in a chemokine receptor CCR7-dependent manner. Likewise, cancer cells that upregulate CCR7 expression are attracted by these chemokines and metastasize to lymphoid organs. In-depth investigation of CCR7 expression and chemokine-mediated signaling is pivotal to understand their role in health and disease. Appropriate fluorescent probes to track these events are increasingly in demand. Here, we present an approach to cost-effectively produce and fluorescently label CCL19 and CCL21 in a semi-automated process. We established a versatile protocol for the production of recombinant chemokines harboring a small C-terminal S6-tag for efficient and site-specific enzymatic labelling with an inorganic fluorescent dye of choice. We demonstrate that the fluorescently labeled chemokines CCL19-S6^Dy649P1 and CCL21-S6^Dy649P1 retain their full biological function as assessed by their abilities to mobilize intracellular calcium, to recruit β-arrestin to engaged receptors and to attract CCR7-expressing leukocytes. Moreover, we show that CCL19-S6^Dy649P1 serves as powerful reagent to monitor CCR7 internalization by time-lapse confocal video microscopy and to stain CCR7-positive primary human and mouse T cell sub-populations.

Does C-C Motif Chemokine Ligand 2 (CCL2) Link Obesity to a Pro-Inflammatory State?

The mechanisms of how obesity contributes to the development of cardio-metabolic diseases are not entirely understood. Obesity is frequently associated with adipose tissue dysfunction, characterized by, e.g., adipocyte hypertrophy, ectopic fat accumulation, immune cell infiltration, and the altered secretion of adipokines. Factors secreted from adipose tissue may induce and/or maintain a local and systemic low-grade activation of the innate immune system. Attraction of macrophages into adipose tissue and altered crosstalk between macrophages, adipocytes, and other cells of adipose tissue are symptoms of metabolic inflammation. Among several secreted factors attracting immune cells to adipose tissue, chemotactic C-C motif chemokine ligand 2 (CCL2) (also described as monocyte chemoattractant protein-1 (MCP-1)) has been shown to play a crucial role in adipose tissue macrophage infiltration. In this review, we aimed to summarize and discuss the current knowledge on CCL2 with a focus on its role in linking obesity to cardio-metabolic diseases.

Inhibition of CCL2 by bindarit alleviates diabetes-associated periodontitis by suppressing inflammatory monocyte infiltration and altering macrophage properties

Diabetes-associated periodontitis (DP) aggravates diabetic complications and increases mortality from diabetes. DP is caused by diabetes-enhanced host immune-inflammatory responses to bacterial insult. In this study, we found that persistently elevated CCL2 levels in combination with proinflammatory monocyte infiltration of periodontal tissues were closely related to DP. Moreover, inhibition of CCL2 by oral administration of bindarit reduced alveolar bone loss and increased periodontal epithelial thickness by suppressing periodontal inflammation. Furthermore, bindarit suppressed the infiltration of proinflammatory monocytes and altered the inflammatory properties of macrophages in the diabetic periodontium. This finding provides a basis for the development of an effective therapeutic approach for treating DP.

Analysis of lung stromal expression of the atypical chemokine receptor ACKR2 reveals unanticipated expression in murine blood endothelial cells

Analysis of chemokine receptor, and atypical chemokine receptor, expression is frequently hampered by the lack of availability of high‐quality antibodies and the species specificity of those that are available. We have previously described methodology utilizing Alexa‐Fluor‐labeled chemokine ligands as versatile reagents to detect receptor expression. Previously this has been limited to hematopoietic cells and methodology for assessing expression of receptors on stromal cells has been lacking. Among chemokine receptors, the ones most frequently expressed on stromal cells belong to the atypical chemokine receptor subfamily. These receptors do not signal in the classic sense in response to ligand but scavenge their ligands and degrade them and thus sculpt in vivo chemokine gradients. Here, we demonstrate the ability to use either intratracheal or intravenous, Alexa‐Fluor‐labeled chemokine administration to detect stromal cell populations expressing the atypical chemokine receptor ACKR2. Using this methodology, we demonstrate, for the first time, expression of ACKR2 on blood endothelial cells. This observation sets the lung aside from other tissues in which ACKR2 is exclusively expressed on lymphatic endothelial cells and suggest unique roles for ACKR2 in the pulmonary environment.

Self-Generated Gradients Yield Exceptionally Robust Steering Cues

Chemotaxis is a widespread mechanism that allows migrating cells to steer to where they are needed. Attractant gradients may be imposed by external sources, or self-generated, when cells create their own steep local gradients by breaking down a prevalent, broadly distributed attractant. Here we show that chemotaxis works far more robustly toward self-generated gradients. Cells can only respond efficiently to a restricted range of attractant concentrations; if attractants are too dilute, their gradients are too shallow for cells to sense, but if they are too high, all receptors become saturated and cells cannot perceive spatial differences. Self-generated gradients are robust because cells maintain the attractant at optimal concentrations. A wave can recruit varying numbers of steered cells, and cells can take time to break down attractant before starting to migrate. Self-generated gradients can therefore operate over a greater range of attractant concentrations, larger distances, and longer times than imposed gradients. The robustness is further enhanced at low cell numbers if attractants also act as mitogens, and at high attractant concentrations if the enzymes that break down attractants are themselves induced by constant attractant levels.

A Fluorescent Activatable AND-Gate Chemokine CCL2 Enables In Vivo Detection of Metastasis-Associated Macrophages

We report the novel chemical design of fluorescent activatable chemokines as highly specific functional probes for imaging subpopulations of immune cells in live tumours. Activatable chemokines behave as AND-gates since they emit only after receptor binding and intracellular activation, showing enhanced selectivity over existing agents. We have applied this strategy to produce mCCL2-MAF as the first probe for in vivo detection of metastasis-associated macrophages in a preclinical model of lung metastasis. This strategy will accelerate the preparation of new chemokine-based probes for imaging immune cell function in tumours.

Chemokine (C-C motif) ligand 2 and coronary artery disease: Tissue expression of functional and atypical receptors

Chemokines, particularly chemokine (C-C- motif) ligand 2 (CCL2), control leukocyte migration into the wall of the artery and regulate the traffic of inflammatory cells. CCL2 is bound to functional receptors (CCR2), but also to atypical chemokine receptors (ACKRs), which do not induce cell migration but can modify chemokine gradients. Whether atherosclerosis alters CCL2 function by influencing the expression of these receptors remains unknown. In a necropsy study, we used immunohistochemistry to explore where and to what extent CCL2 and related receptors are present in diseased arteries that caused the death of men with coronary artery disease compared with unaffected arteries. CCL2 was marginally detected in normal arteries but was more frequently found in the intima. The expression of CCL2 and related receptors was significantly increased in diseased arteries with relative differences among the artery layers. The highest relative increases were those of CCL2 and ACKR1. CCL2 expression was associated with a significant predictive value of atherosclerosis. Findings suggest the need for further insight into receptor specificity or activity and the interplay among chemokines. CCL2-associated conventional and atypical receptors are overexpressed in atherosclerotic arteries, and these may suggest new potential therapeutic targets to locally modify the overall anti-inflammatory response.

Nonmotile Single-Cell Migration as a Random Walk in Nonuniformity: The "Extreme Dumping Limit" for Cell-to-Cell Communications

In the present work, we model single-cell movement as a random walk in an external potential observed within the extreme dumping limit, which we define herein as the extreme nonuniform behavior observed for cell responses and cell-to-cell communications. Starting from the Newton–Langevin equation of motion, we solve the corresponding Fokker–Planck equation to compute higher moments of the displacement of the cell, and then we build certain quantities that can be measurable experimentally. We show that, each time, the dynamics depend on the external force applied, leading to predictions distinct from the standard results of a free Brownian particle. Our findings demonstrate that cell migration viewed as a stochastic process is still compatible with biological and experimental observations without the need to rely on more complicated or sophisticated models proposed previously in the literature.

The Atypical Chemokine Receptor Ackr2 Constrains NK Cell Migratory Activity and Promotes Metastasis

Chemokines have been shown to be essential players in a range of cancer contexts. In this study, we demonstrate that mice deficient in the atypical chemokine receptor Ackr2 display impaired development of metastasis in vivo in both cell line and spontaneous models. Further analysis reveals that this relates to increased expression of the chemokine receptor CCR2, specifically by KLRG1⁺ NK cells from the Ackr2^−/− mice. This leads to increased recruitment of KLRG1⁺ NK cells to CCL2-expressing tumors and enhanced tumor killing. Together, these data indicate that Ackr2 limits the expression of CCR2 on NK cells and restricts their tumoricidal activity. Our data have important implications for our understanding of the roles for chemokines in the metastatic process and highlight Ackr2 and CCR2 as potentially manipulable therapeutic targets in metastasis.

Expression of the Atypical Chemokine Receptor ACKR4 Identifies a Novel Population of Intestinal Submucosal Fibroblasts That Preferentially Expresses Endothelial Cell Regulators

Atypical chemokine receptors (ACKRs) are expressed by discrete populations of stromal cells at specific anatomical locations where they control leukocyte migration by scavenging or transporting chemokines. ACKR4 is an atypical receptor for CCL19, CCL21, and CCL25. In skin, ACKR4 plays indispensable roles in regulating CCR7-dependent APC migration, and there is a paucity of migratory APCs in the skin-draining lymph nodes of Ackr4-deficient mice under steady-state and inflammatory conditions. This is caused by loss of ACKR4-mediated CCL19/21 scavenging by keratinocytes and lymphatic endothelial cells. In contrast, we show in this study that Ackr4 deficiency does not affect dendritic cell abundance in the small intestine and mesenteric lymph nodes, at steady state or after R848-induced mobilization. Moreover, Ackr4 expression is largely restricted to mesenchymal cells in the intestine, where it identifies a previously uncharacterized population of fibroblasts residing exclusively in the submucosa. Compared with related Ackr4^- mesenchymal cells, these Ackr4⁺ fibroblasts have elevated expression of genes encoding endothelial cell regulators and lie in close proximity to submucosal blood and lymphatic vessels. We also provide evidence that Ackr4⁺ fibroblasts form physical interactions with lymphatic endothelial cells, and engage in molecular interactions with these cells via the VEGFD/VEGFR3 and CCL21/ACKR4 pathways. Thus, intestinal submucosal fibroblasts in mice are a distinct population of intestinal mesenchymal cells that can be identified by their expression of Ackr4 and have transcriptional and anatomical properties that strongly suggest roles in endothelial cell regulation.

Chemokine Transport Dynamics and Emerging Recognition of Their Role in Immune Function

Leukocyte migration is critically important during all protective and pathological immune and inflammatory responses. Chemokines play fundamental roles in this process, and chemokine concentration gradients stimulate the directional migration of leukocytes. The formation and regulation of these gradients is poorly understood. These are complex processes that depend on the specific properties of each chemokine and interactions between physical, biological and biochemical processes, including production, diffusion, advection, scavenging, post-translational modification, and extracellular matrix (ECM) binding. While some of these mechanisms have been investigated in isolation or limited combinations, more integrative research is required to provide a quantitative knowledge base that explains how chemokine gradients are established and maintained, and how cells respond to, and modify, these gradients.

Role of Gut Inflammation in Altering the Monocyte Compartment and Its Osteoclastogenic Potential in HLA-B27-Transgenic Rats

OBJECTIVE

To investigate the relationship between intestinal inflammation and the central and peripheral innate immune system in the pathogenesis of HLA-B27-associated spondyloarthritis using an HLA-B27-transgenic (B27-Tg) rat model.

METHODS

The myeloid compartment of the blood and bone marrow (BM) of B27-Tg rats, as well as HLA-B7-Tg and non-Tg rats as controls, was evaluated by flow cytometry. Plasma from rats was assessed by enzyme-linked immunosorbent assay for levels of CCL2 and interleukin-1α (IL-1α). Rats were treated with antibiotics for 4 weeks, and the myeloid compartment of the blood and BM was evaluated by flow cytometry. The osteoclastogenic potential of BM-derived cells from antibiotic-treated rats, in the presence or absence of tumor necrosis factor (TNF), was evaluated in vitro.

RESULTS

B27-Tg rats had substantially higher numbers of circulating Lin-CD172a+CD43^low monocytes as compared to control animals, and this was significantly correlated with higher levels of plasma CCL2. Antibiotic treatment of B27-Tg rats markedly reduced the severity of ileitis, plasma levels of CCL2 and IL-1α, and number of BM and blood Lin-CD172a+CD43^low monocytes, a cell subset shown in the present study to have the greatest in vitro osteoclastogenic potential. Antibiotic treatment also prevented the TNF-dependent enhancement of osteoclastogenesis in B27-Tg rats.

CONCLUSION

Microbiota-dependent intestinal inflammation in B27-Tg rats directly drives the systemic inflammatory and bone-erosive potential of the monocyte compartment.

Modulation of Host Immunity by the Human Metapneumovirus

Globally, as a leading agent of acute respiratory tract infections in children <5 years of age and the elderly, the human metapneumovirus (HMPV) has gained considerable attention. As inferred from studies comparing vaccinated and experimentally infected mice, the acquired immune response elicited by this pathogen fails to efficiently clear the virus from the airways, which leads to an exaggerated inflammatory response and lung damage. Furthermore, after disease resolution, there is a poor development of T and B cell immunological memory, which is believed to promote reinfections and viral spread in the community. In this article, we discuss the molecular mechanisms that shape the interactions of HMPV with host tissues that lead to pulmonary pathology and to the development of adaptive immunity that fails to protect against natural infections by this virus.

Self-generated chemotactic gradients-cells steering themselves

Chemotaxis is a fundamentally important part of biology, but we know very little about how gradients of chemoattractant are formed. One answer is self-generated gradients, in which the moving cells break down the attractant to provide their own gradient as they migrate. Here we discuss where self-generated gradients are known, how they can be recognized, and where they are likely to be found in the future.

CCR2 Influences T Regulatory Cell Migration to Tumors and Serves as a Biomarker of Cyclophosphamide Sensitivity

The CCL2 chemokine receptor CCR2 drives cancer by mediating the recruitment of monocytes and myeloid-derived suppressor cells to the tumor microenvironment. In this study, we extend the significance of CCR2 in this setting by identifying a new role for it in mediating recruitment of CD4⁺ T regulatory cells (Treg). Following tumor initiation, an expanded population of CCR2⁺ Tregs required CCR2 expression to traffic between draining lymph nodes (dLN) and the tumor. This Treg subset was enriched in the fraction of tumor antigen-specific cells in the dLN, where they displayed an activated immunosuppressive phenotype. Notably, in mouse models, low-dose cyclophosphamide treatment preferentially depleted CCR2⁺ Treg, enhancing priming of tumor-specific CD8⁺ T cells. In the MMTV-PyMT transgenic mouse model of breast cancer and in oral squamous cell carcinoma patients, tumor development was associated with decreased blood frequency and inversely increased tumor frequency of CCR2⁺ Tregs. Our results define a novel subset of CCR2⁺ Treg involved in tumoral immune escape, and they offer evidence that this Treg subset may be preferentially eradicated by low-dose cyclophosphamide treatment. Cancer Res; 76(22); 6483-94. ©2016 AACR.

Carcinoembryonic Antigen Cell Adhesion Molecule 1 long isoform modulates malignancy of poorly differentiated colon cancer cells

OBJECTIVE

Nearly 20%-29% of patients with colorectal cancer (CRC) succumb to liver or lung metastasis and there is a dire need for novel targets to improve the survival of patients with metastasis. The long isoform of the Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1-L or CC1-L) is a key regulator of immune surveillance in primary CRC, but its role in metastasis remains largely unexplored. We have examined how CC1-L expression impacts on colon cancer liver metastasis.

DESIGN

Murine MC38 transfected with CC1-L were evaluated in vitro for proliferation, migration and invasion, and for in vivo experimental liver metastasis. Using shRNA silencing or pharmacological inhibition, we delineated the role in liver metastasis of Chemokine (C-C motif) Ligand 2 (CCL2) and Signal Transducer and Activator of Transcription 3 (STAT3) downstream of CC1-L. We further assessed the clinical relevance of these findings in a cohort of patients with CRC.

RESULTS

MC38-CC1-L-expressing cells exhibited significantly reduced in vivo liver metastasis and displayed decreased CCL2 chemokine secretion and reduced STAT3 activity. Down-modulation of CCL2 expression and pharmacological inhibition of STAT3 activity in MC38 cells led to reduced cell invasion capacity and decreased liver metastasis. The clinical relevance of our findings is illustrated by the fact that high CC1 expression in patients with CRC combined with some inflammation-regulated and STAT3-regulated genes correlate with improved 10-year survival.

CONCLUSIONS

CC1-L regulates inflammation and STAT3 signalling and contributes to the maintenance of a less-invasive CRC metastatic phenotype of poorly differentiated carcinomas.

ACKR4 on Stromal Cells Scavenges CCL19 To Enable CCR7-Dependent Trafficking of APCs from Inflamed Skin to Lymph Nodes

Dermal dendritic cells and epidermal Langerhans cells are APCs that migrate from skin to draining lymph nodes (LN) to drive peripheral tolerance and adaptive immunity. Their migration requires the chemokine receptor CCR7, which directs egress from the skin via dermal lymphatic vessels and extravasation into the LN parenchyma from lymph in the subcapsular sinus. CCR7 is activated by two chemokines: CCL19 and CCL21. CCL21 alone is sufficient for the migration of APCs from skin to LN. CCL19 and CCL21 also bind atypical chemokine receptor (ACKR) 4. ACKR4-mediated CCL21 scavenging by lymphatic endothelial cells lining the subcapsular sinus ceiling stabilizes interfollicular CCL21 gradients that direct lymph-borne CCR7(+)APCs into the parenchyma of mouse LN. In this study, we show that ACKR4 also aids APC egress from mouse skin under steady-state and inflammatory conditions. ACKR4 plays a particularly prominent role during cutaneous inflammation when it facilitates Langerhans cell egress from skin and enables the accumulation of dermal dendritic cells in skin-draining LN. Stromal cells in mouse skin, predominantly keratinocytes and a subset of dermal lymphatic endothelial cells, express ACKR4 and are capable of ACKR4-dependent chemokine scavenging in situ. ACKR4-mediated scavenging of dermal-derived CCL19, rather than CCL21, is critical during inflammation, because the aberrant trafficking of skin-derived APCs inAckr4-deficient mice is completely rescued by genetic deletion ofCcl19 Thus, ACKR4 on stromal cells aids the egress of APCs from mouse skin, and, during inflammation, facilitates CCR7-dependent cell trafficking by scavenging CCL19.

Spinal Cord T-Cell Infiltration in the Rat Spared Nerve Injury Model: A Time Course Study

The immune system is involved in the development of neuropathic pain. In particular, the infiltration of T-lymphocytes into the spinal cord following peripheral nerve injury has been described as a contributor to sensory hypersensitivity. We used the spared nerve injury (SNI) model of neuropathic pain in Sprague Dawley adult male rats to assess proliferation, and/or protein/gene expression levels for microglia (Iba1), T-lymphocytes (CD2) and cytotoxic T-lymphocytes (CD8). In the dorsal horn ipsilateral to SNI, Iba1 and BrdU stainings revealed microglial reactivity and proliferation, respectively, with different durations. Iba1 expression peaked at D4 and D7 at the mRNA and protein level, respectively, and was long-lasting. Proliferation occurred almost exclusively in Iba1 positive cells and peaked at D2. Gene expression observation by RT-qPCR array suggested that T-lymphocytes attracting chemokines were upregulated after SNI in rat spinal cord but only a few CD2/CD8 positive cells were found. A pronounced infiltration of CD2/CD8 positive T-cells was seen in the spinal cord injury (SCI) model used as a positive control for lymphocyte infiltration. Under these experimental conditions, we show early and long-lasting microglia reactivity in the spinal cord after SNI, but no lymphocyte infiltration was found.

A genome-wide association study of fetal response to type 2 porcine reproductive and respiratory syndrome virus challenge

Control of porcine reproductive and respiratory syndrome (PRRS) is economically important for the swine industry worldwide. As current PRRS vaccines do not completely protect against heterologous challenge, alternative means of control, including enhanced genetic resilience, are needed. For reproductive PRRS, the genetic basis of fetal response to PRRS virus (PRRSV) infection is poorly understood. Genome-wide association studies (GWAS) were done here using data from 928 fetuses from pregnant gilts experimentally challenged with type 2 PRRSV. Fetuses were assessed for viral load in thymus (VLT), viral load in endometrium (VLE), fetal death (FD) and fetal viability (FV), and genotyped at a medium density. Collectively, 21 candidate genomic regions were found associated with these traits, seven of which overlap with previously reported QTLs for pig health and reproduction. A comparison with ongoing and related transcriptomic analyses of fetal response to PRRSV infection found differentially expressed genes within 18 candidate regions. Some of these genes have immune system functions, and have been reported to contribute to host response to PRRSV infection. The results provide new evidence about the genetic basis of fetal response to PRRSV challenge, and may ultimately lead to alternative control strategies to reduce the impact of reproductive PRRS.

Overview and potential unifying themes of the atypical chemokine receptor family

Chemokines modulate immune responses through their ability to orchestrate the migration of target cells. Chemokines directly induce cell migration through a distinct set of 7 transmembrane domain G protein-coupled receptors but are also recognized by a small subfamily of atypical chemokine receptors, characterized by their inability to support chemotactic activity. Atypical chemokine receptors are now emerging as crucial regulatory components of chemokine networks in a wide range of physiologic and pathologic contexts. Although a new nomenclature has been approved recently to reflect their functional distinction from their conventional counterparts, a systematic view of this subfamily is still missing. This review discusses their biochemical and immunologic properties to identify potential unifying themes in this emerging family.

Monitoring Scavenging Activity of Chemokine Receptors

Migration and positioning of cells is fundamental for complex functioning of multicellular organisms. During an immune response, cells are recruited from remote distances to a distinct location. Cells that are passively transported leave the circulation stimulated by locally produced signals and follow chemotactic cues to reach specific destinations. Such gradients are short (<150 μm) and require a source of production where the concentration is the highest and a sink in apposition where the attractant dissipates and the concentration is the lowest. Several straight forward methods exist to identify in vitro and in vivo cells producing chemoattractants. This can be achieved at the transcriptional level and by measuring secreted proteins. However, to demonstrate the activity of sinks in vitro and in vivo is more challenging. Cell-mediated dissipation of an attractant must be revealed by measuring its uptake and subsequent destruction. Elimination of chemoattractants such as chemokines can be monitored in vitro using radiolabeled ligands or more elegantly with fluorescent-labeled chemoattractants. The latter method can also be used in vivo and enables to monitor the process in real time using time-lapse video microscopy. In this chapter, we describe methods to produce fluorescently labeled chemokines either as fusion proteins secreted from insect cells or as recombinant bacterial proteins that can enzymatically be labeled. We discuss methods that were successfully used to demonstrate sink activities of scavenger receptors. Moreover, fluorescent chemokines can be used to noninvasively analyze receptor expression and activity in living cells.

CCR2 inhibition sequesters multiple subsets of leukocytes in the bone marrow

Chemokine receptor CCR2 mediates monocyte mobilization from the bone marrow (BM) and subsequent migration into target tissues. The degree to which CCR2 is differentially expressed in leukocyte subsets, and the contribution of CCR2 to these leukocyte mobilization from the BM are poorly understood. Using red fluorescence protein CCR2 reporter mice, we found heterogeneity in CCR2 expression among leukocyte subsets in varying tissues. CCR2 was highly expressed by inflammatory monocytes, dendritic cells, plasmacytoid dendritic cells and NK cells in all tissues. Unexpectedly, more than 60% of neutrophils expressed CCR2, albeit at low levels. CCR2 expression in T cells, B cells and NK T cells was greatest in the BM compared to other tissues. Genetic CCR2 deficiency markedly sequestered all leukocyte subsets in the BM, with reciprocal reduction noted in the peripheral blood and spleen. CCR2 inhibition via treatment with CCR2 signaling inhibitor propagermanium produced similar effects. Propagermanium also mitigated lipopolysaccharide-induced BM leukocyte egress. Consistent with its functional significance, CCR2 antibody staining revealed surface CCR2 expression within a subset of BM neutrophils. These results demonstrate the central role CCR2 plays in mediating leukocyte mobilization from the BM, and suggest a role for CCR2 inhibition in managing monocytes/macrophages-mediated chronic inflammatory conditions.

Thymic CCL2 influences induction of T-cell tolerance

Thymic epithelial cells (TEC) and dendritic cells (DC) play a role in T cell development by controlling the selection of the T cell receptor repertoire. DC have been described to take up antigens in the periphery and migrate into the thymus where they mediate tolerance via deletion of autoreactive T cells, or by induction of natural regulatory T cells. Migration of DC to thymus is driven by chemokine receptors. CCL2, a major ligand for the chemokine receptor CCR2, is an inflammation-associated chemokine that induces the recruitment of immune cells in tissues. CCL2 and CCR2 are implicated in promoting experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis. We here show that CCL2 is constitutively expressed by endothelial cells and TEC in the thymus. Transgenic mice overexpressing CCL2 in the thymus showed an increased number of thymic plasmacytoid DC and pronounced impairment of T cell development. Consequently, CCL2 transgenic mice were resistant to EAE. These findings demonstrate that expression of CCL2 in thymus regulates DC homeostasis and controls development of autoreactive T cells, thus preventing development of autoimmune diseases.