Rôle des monocytes dans la régulation de la réponse inflammatoire au cours du sepsis

Sepsis is a common and life-threatening pathology. It is defined as an organic dysfunction caused by a dysregulated host response to infection. An initial hyper-inflammatory phase follows recognition of the pathogen and is progressively replaced by long-term immunosuppression leading to prolonged sensitivity to superinfections. Monocytes (Mo) are one of the first lines of phagocytic cells in the lung. Understanding how these cells participate in pulmonary supervision during sepsis would allow the development or improvement of treatments for enhancing resistance to secondary nosocomial infections. We showed that monocytes are strongly involved in the control of inflammation during the early and late phases of murine polymicrobial sepsis. Indeed, during the acute phase of sepsis, inflammatory monocyte mobilization participates to the monitoring of renal tissues and has a protective effect via a CX3CR1-dependent adhesion mechanism. The second phase of sepsis is most often described as “immunosuppressive”. We demonstrated a systemic accumulation of myeloid cells during this last phase. Characterization of their localization showed that these cells accumulated specifically in the vascular network of the organs without infiltrating the tissues. Ly6Chigh monocytes and their chemokine receptors CCR2 and CX3CR1 have been identified as essential for pulmonary supervision during first and second infection. However, the ability of these cells to stimulate and regulate immune responses appears to be impaired. Thus, the activation state of inflammatory Mo would not protect against a second pulmonary infections post sepsis.Le sepsis est une pathologie fréquente et grave. Il est défini comme un dysfonctionnement organique causé par une réponse dérégulée de l’hôte envers une infection. Une phase hyperinflammatoire précoce fait suite à la reconnaissance de l’agent pathogène et est progressivement remplacée par une immunosuppression à long terme entrainant une sensibilité prolongée des patients aux infections nosocomiales. Nos travaux ont montré que les Mo inflammatoires étaient fortement impliqués dans le contrôle de l’inflammation durant les phases précoces et tardives au cours d’un sepsis polymicrobien murin. En effet, lors de la phase « hyper-aiguë » la mobilisation des Mo participe à la surveillance et à la protection des tissus rénaux grâce à des mécanismes d’adhésion cellulaire dépendant du récepteur CX3CR1. La seconde phase du sepsis est le plus souvent décrite comme « immunosuppressive ». Nous avons mis en évidence une accumulation systémique des Mo et des PMN durant cette dernière phase. La caractérisation de leur localisation a montré que ces cellules s’accumulaient spécifiquement dans le réseau vasculaire des organes sans infiltrer les tissus. Les Mo Ly6Chigh et leurs récepteurs aux chimiokines CCR2 et CX3CR1 ont été identifiés comme essentiels à la surveillance pulmonaire lors d’une infection secondaire au sepsis. Cependant, la capacité de ces cellules à stimuler et à réguler les réponses immunitaires semble être altérée. Ainsi, l’état d’activation des Mo inflammatoires ne permettrait pas une protection efficace contre les infections opportunistes pulmonaires secondaires au sepsis

Role of monocytes in the regulation of inflammatory response during sepsis

Le sepsis est une pathologie fréquente et grave. Il est défini comme un dysfonctionnement organique causé par une réponse dérégulée de l’hôte envers une infection. Une phase hyperinflammatoire précoce fait suite à la reconnaissance de l’agent pathogène et est progressivement remplacée par une immunosuppression à long terme entrainant une sensibilité prolongée des patients aux infections nosocomiales. Nos travaux ont montré que les Mo inflammatoires étaient fortement impliqués dans le contrôle de l’inflammation durant les phases précoces et tardives au cours d’un sepsis polymicrobien murin. En effet, lors de la phase « hyper-aiguë » la mobilisation des Mo participe à la surveillance et à la protection des tissus rénaux grâce à des mécanismes d’adhésion cellulaire dépendant du récepteur CX3CR1. La seconde phase du sepsis est le plus souvent décrite comme « immunosuppressive ». Nous avons mis en évidence une accumulation systémique des Mo et des PMN durant cette dernière phase. La caractérisation de leur localisation a montré que ces cellules s’accumulaient spécifiquement dans le réseau vasculaire des organes sans infiltrer les tissus. Les Mo Ly6Chigh et leurs récepteurs aux chimiokines CCR2 et CX3CR1 ont été identifiés comme essentiels à la surveillance pulmonaire lors d’une infection secondaire au sepsis. Cependant, la capacité de ces cellules à stimuler et à réguler les réponses immunitaires semble être altérée. Ainsi, l’état d’activation des Mo inflammatoires ne permettrait pas une protection efficace contre les infections opportunistes pulmonaires secondaires au sepsis.Sepsis is a common and life-threatening pathology. It is defined as an organic dysfunction caused by a dysregulated host response to infection. An initial hyper-inflammatory phase follows recognition of the pathogen and is progressively replaced by long-term immunosuppression leading to prolonged sensitivity to superinfections. Monocytes (Mo) are one of the first lines of phagocytic cells in the lung. Understanding how these cells participate in pulmonary supervision during sepsis would allow the development or improvement of treatments for enhancing resistance to secondary nosocomial infections. We showed that monocytes are strongly involved in the control of inflammation during the early and late phases of murine polymicrobial sepsis. Indeed, during the acute phase of sepsis, inflammatory monocyte mobilization participates to the monitoring of renal tissues and has a protective effect via a CX3CR1-dependent adhesion mechanism. The second phase of sepsis is most often described as “immunosuppressive”. We demonstrated a systemic accumulation of myeloid cells during this last phase. Characterization of their localization showed that these cells accumulated specifically in the vascular network of the organs without infiltrating the tissues. Ly6Chigh monocytes and their chemokine receptors CCR2 and CX3CR1 have been identified as essential for pulmonary supervision during first and second infection. However, the ability of these cells to stimulate and regulate immune responses appears to be impaired. Thus, the activation state of inflammatory Mo would not protect against a second pulmonary infections post sepsis

CX3CR1-dependent endothelial margination modulates Ly6Chigh monocyte systemic deployment upon inflammation in mice

International audienceTwo subsets of blood monocytes are commonly described in mice and humans: the classical inflammatory monocytes, which are rapidly mobilized upon inflammation in a CC-chemokine receptor 2-dependent manner, and the nonclassical blood resident monocyte subset that patrols the intraluminal side of the endothelium. Old reports suggest that blood monocytes are distributed into circulating and marginating pools, but no direct evidence of the latter has been obtained so far. Using a combination of in vivo real-time imaging and blood/tissue partitioning by intravascular staining of leukocytes, we showed that both inflammatory and resident monocytes are retained in the bone marrow vasculature, representing an important reservoir of marginated monocytes. Upon lipopolysaccharide or cecal ligation and puncture-induced peritonitis, these marginated cells are rapidly released and recruited to the peritoneum membrane lumen vasculature where they reside through CX3C-chemokine receptor 1 (CX3CR1)-dependent adherence. At a later time point, inflammatory monocytes infiltrate the spleen parenchyma but remain mainly intravascular in the vicinity of the lungs and the peritoneum. Our results show that this monocyte deployment is controlled by a CX3CR1-dependent balance between marginating and circulating monocytes and highlight that tissue infiltration is not a mandatory fate for inflammatory monocytes

Analysis of monocyte infiltration in MPTP mice reveals that microglial CX3CR1 protects against neurotoxic over-induction of monocyte-attracting CCL2 by astrocytes

International audienceAbstractBackgroundEvidence from mice suggests that brain infiltrating immune cells contribute to neurodegeneration, and we previously identified a deleterious lymphocyte infiltration in Parkinson’s disease mice. However, this remains controversial for monocytes, due to artifact-prone techniques used to distinguish them from microglia. Our aim was to reassess this open question, by taking advantage of the recent recognition that chemokine receptors CCR2 and CX3CR1 can differentiate between inflammatory monocytes and microglia, enabling to test whether CCR2+ monocytes infiltrate the brain during dopaminergic (DA) neurodegeneration and whether they contribute to neuronal death. This revealed unexpected insights into possible regulation of monocyte-attracting CCL2 induction.MethodsWe used acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mice and assessed monocyte infiltration by combining laser microdissection-guided chemokine RNA profiling of the substantia nigra (SN) with immunohistochemistry and CCR2-GFP reporter mice. To determine contribution to neuronal loss, we used CCR2-deletion and CCL2-overexpression, to reduce and increase CCR2+ monocyte infiltration, and CX3CR1-deletion to assess a potential implication in CCL2 regulation.ResultsNigral chemokine profiling revealed early CCL2/7/12-CCR2 axis induction, suggesting monocyte infiltration in MPTP mice. CCL2 protein showed early peak induction in nigral astrocytes, while CCR2-GFP mice revealed early but limited nigral monocyte infiltration. However, blocking infiltration by CCR2 deletion did not influence DA neuronal loss. In contrast, transgenic astrocytic CCL2 over-induction increased CCR2+ monocyte infiltration and DA neuronal loss in MPTP mice. Surprisingly, CCL2 over-induction was also detected in MPTP intoxicated CX3CR1-deleted mice, which are known to present increased DA neuronal loss. Importantly, CX3CR1/CCL2 double-deletion suggested that increased neurotoxicity was driven by astrocytic CCL2 over-induction.ConclusionsWe show that CCR2+ monocytes infiltrate the affected CNS, but at the level observed in acute MPTP mice, this does not contribute to DA neuronal loss. In contrast, the underlying astrocytic CCL2 induction seemed to be tightly controled, as already moderate CCL2 over-induction led to increased neurotoxicity in MPTP mice, likely due to the increased CCR2+ monocyte infiltration. Importantly, we found evidence suggesting that during DA neurodegeneration, this control was mediated by microglial CX3CR1 signaling, which protects against such neurotoxic CCL2 over-induction by astrocytes, thus hinting at an endogenous mechanism to limit neurotoxic effects of the CCL2-CCR2 axis

Sepsis Triggers a Late Expansion of Functionally Impaired Tissue-Vascular Inflammatory Monocytes During Clinical Recovery

International audienceSepsis is characterized by a systemic inflammation that can cause an immune dysfunction, for which the underlying mechanisms are unclear. We investigated the impact of cecal ligature and puncture (CLP)-mediated polymicrobial sepsis on monocyte (Mo) mobilization and functions. Our results show that CLP led to two consecutive phases of Mo deployment. The first one occurred within the first 3 days after the induction of the peritonitis, while the second phase was of a larger amplitude and extended up to a month after apparent clinical recovery. The latter was associated with the expansion of Mo in the tissue reservoirs (bone marrow and spleen), their release in the blood and their accumulation in the vasculature of peripheral non-lymphoid tissues. It occurred even after antibiotic treatment but relied on inflammatory-dependent pathways and inversely correlated with increased susceptibility and severity to a secondary infection. The intravascular lung Mo displayed limited activation capacity, impaired phagocytic functions and failed to transfer efficient protection against a secondary infection into monocytopenic CCR2-deficient mice. In conclusion, our work unveiled key dysfunctions of intravascular inflammatory Mo during the recovery phase of sepsis and provided new insights to improve patient protection against secondary infections

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

International audienceThe 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

Smoking and Diet: Impact on Disease Course?

International audienceThe impact of current smoking on inflammatory bowel disease (IBD) course has been studied extensively; smoking is deleterious in Crohn's disease (CD), and beneficial in ulcerative colitis (UC). Except for enteral nutrition, there are only limited data regarding the impact of diet on disease course. Key Messages: Current smoking worsens the course of CD, increasing the incidence of flares, the need for steroids, immunosuppressants and re-operations. Conversely, smoking cessation has a rapid beneficial effect on disease course, decreasing the risk of flares and of post-operative recurrences. From 3 months after the quit date, quitters have a disease course similar to that of never smokers. Achieving smoking cessation in CD is thus an important goal of therapy. On the contrary, smoking improves the course of UC and in particular, is associated with a decreased need for colectomy. Smoking cessation increases the risk of flare and the need for steroids or immunosuppressants. However, patients with UC should not be discouraged to quit, because the beneficial effect of smoking for their disease is counterbalanced by the deleterious systemic effects of tobacco. Among dietary interventions, only exclusive enteral nutrition was shown to induce remission and achieve mucosal healing in some patients with CD. The beneficial effect of liquid-defined diet is observed whatever be the type of administration (orally or by tube), the type of diet regarding protein and fat content and resulting alterations in the gut microbiota. In UC, enteral nutrition has no effect. Finally, popularized restrictive diets in IBD as the specific-carbohydrate diet and the gluten-free diet have not been rigorously tested. In a small trial, a semi-vegetarian diet was shown to be effective in maintaining remission over 2 years in CD. Patients with IBD should not smoke and avoid passive smoking. Aside from the defined liquid diets, there is no rationale for advising particular diets

Macrophages of distinct origins contribute to tumor development in the lung

International audienceTissue-resident macrophages can self-maintain without contribution of adult hematopoiesis. Herein we show that tissue-resident interstitial macrophages (Res-TAMs) in mouse lungs contribute to the pool of tumor-associated macrophages (TAMs) together with CCR2-dependent recruited macrophages (MoD-TAMs). Res-TAMs largely correlated with tumor cell growth in vivo, while MoD-TAMs accumulation was associated with enhanced tumor spreading. Both cell subsets were depleted after chemotherapy, but MoD-TAMs rapidly recovered and performed phagocytosis-mediated tumor clearance. Interestingly, anti-VEGF treatment combined with chemotherapy inhibited both Res and Mod-TAM reconstitution without affecting monocyte infiltration and improved its efficacy. Our results reveal that the developmental origin of TAMs dictates their relative distribution, function, and response to cancer therapies in lung tumors

CX3CR1 deficiency promotes muscle repair and regeneration by enhancing macrophage ApoE production

International audienceMuscle injury triggers inflammation in which infiltrating mononuclear phagocytes are crucial for tissue regeneration. The interaction of the CCL2/CCR2 and CX3CL1/CX3CR1 chemokine axis that guides phagocyte infiltration is incompletely understood. Here, we show that CX3CR1 deficiency promotes muscle repair and rescues Ccl2 (-/-) mice from impaired muscle regeneration as a result of altered macrophage function, not infiltration. Transcriptomic analysis of muscle mononuclear phagocytes reveals that Apolipoprotein E (ApoE) is upregulated in mice with efficient regeneration. ApoE treatment enhances phagocytosis by mononuclear phagocytes in vitro, and restores phagocytic activity and muscle regeneration in Ccl2 (-/-) mice. Because CX3CR1 deficiency may compensate for defective CCL2-dependant monocyte recruitment by modulating ApoE-dependent macrophage phagocytic activity, targeting CX3CR1 expressed by macrophages might be a powerful therapeutic approach to improve muscle regeneration