The stunning clodronate

C-reactive protein orchestrates acute allograft rejection in vascularized composite allotransplantation via selective activation of monocyte subsets

INTRODUCTION

Despite advancements in transplant immunology and vascularized composite allotransplantation (VCA), the longevity of allografts remains hindered by the challenge of allograft rejection. The acute-phase response, an immune-inflammatory reaction to ischemia/reperfusion that occurs directly after allogeneic transplantation, serves as a catalyst for graft rejection. This immune response is orchestrated by acute-phase reactants through intricate crosstalk with the mononuclear phagocyte system.

OBJECTIVE

C-reactive protein (CRP), a well-known marker of inflammation, possesses pro-inflammatory properties and exacerbates ischemia/reperfusion injury. Thus, we investigated how CRP impacts acute allograft rejection.

METHODS

Prompted by clinical observations in facial VCAs, we employed a complex hindlimb transplantation model in rats to investigate the direct impact of CRP on transplant rejection.

RESULTS

Our findings demonstrate that CRP expedites allograft rejection and diminishes allograft survival by selectively activating non-classical monocytes. Therapeutic stabilization of CRP abrogates this activating effect on monocytes, thereby attenuating acute allograft rejection. Intravital imagining of graft-infiltrating, recipient-derived monocytes during the early phase of acute rejection corroborated their differential regulation by CRP and their pivotal role in driving the initial stages of graft rejection.

CONCLUSION

The differential activation of recipient-derived monocytes by CRP exacerbates the innate immune response and accelerates clinical allograft rejection. Thus, therapeutic targeting of CRP represents a novel and promising strategy for preventing acute allograft rejection and potentially mitigating chronic allograft rejection.

Rev-erb-α antagonism in alveolar macrophages protects against pneumococcal infection in elderly mice

Circadian rhythms control the diurnal nature of many physiological, metabolic, and immune processes. We hypothesized that age-related impairments in circadian rhythms are associated with high susceptibility to bacterial respiratory tract infections. Our data show that the time-of-day difference in the control of Streptococcus pneumoniae infection is altered in elderly mice. A lung circadian transcriptome analysis revealed that aging alters the daily oscillations in the expression of a specific set of genes and that some pathways that are rhythmic in young-adult mice are non-rhythmic or time shifted in elderly mice. In particular, the circadian expression of the clock component Rev-erb-α and apelin/apelin receptor was altered in elderly mice. In young-adult mice, we discovered an interaction between Rev-erb-α and the apelinergic axis that controls host defenses against S. pneumoniae via alveolar macrophages. Pharmacological repression of Rev-erb-α in elderly mice resulted in greater resistance to pneumococcal infection. These data suggest the causative role of age-associated impairments in circadian rhythms on respiratory infections and have clinical relevance.

Clodronate liposome-mediated macrophage depletion ameliorates iron overload-induced dry eye disease

Dry eye disease (DED) is a prevalent ophthalmic disease that affects millions of people worldwide. Iron overload and macrophage inflammation have been implicated in the development of murine DED, though the specific role of macrophages under iron overload conditions remains unclear. This study aimed to establish a novel iron overload-induced mouse model of DED and investigate macrophage involvement. The model was induced via intraperitoneal injection of D-glucoside iron. Results showed that macrophage depletion via clodronate liposomes (CL) significantly mitigated iron deposit, decreased ocular surface inflammation, improved tear production and restored the structure of ocular surface tissues. Furthermore, CL specifically targeted pro-inflammatory M1 macrophages and reduced levels of the inflammatory cytokines IL-1β, IL-6, and TNF-α, effectively alleviating symptoms of DED. In conclusion, this study characterized a novel iron overload-induced DED mouse model and demenstrated that macrophage depletion mitigated the pathological changes in ocular surface and lacrimal gland tissues caused by iron overload, suggesting potential therapeutic strategies for further investigation in the treatment of DED.

Diverse Functions of Macrophages in Obesity and Metabolic Dysfunction-Associated Steatotic Liver Disease: Bridging Inflammation and Metabolism

Macrophages play crucial roles in immune response and tissue homeostasis, with their functions becoming increasingly complex in obesity-mediated metabolic disorders. This review explores the extensive range of macrophage activities within adipose and liver tissues, emphasizing their contribution to the pathogenesis and progression of obesity and its related metabolic dysfunction-associated steatotic liver disease (MASLD). In the context of obesity, macrophages respond adaptively to lipid overloads and inflammatory cues in adipose tissue, profoundly influencing insulin resistance and metabolic homeostasis. Concurrently, their role in the liver extends to moderating inflammation and orchestrating fibrotic responses, integral to the development of MASLD. Highlighting the spectrum of macrophage phenotypes across these metabolic landscapes, we summarize their diverse roles in linking inflammatory processes with metabolic functions. This review advocates for a deeper understanding of macrophage subsets in metabolic tissues, proposing targeted research to harness their therapeutic potential in mitigating MASLD and other metabolic disorders.

Formononetin ameliorates dextran sulfate sodium-induced colitis via enhancing antioxidant capacity, promoting tight junction protein expression and reshaping M1/M2 macrophage polarization balance

Ulcerative colitis (UC) is a complex, refractory inflammatory bowel disease characterized impared intestinal mucosal barrier and imbalanced M1/M2 macrophage polarization mediating its progression. Formononetin (FN), a bioactive isoflavone with established anti-inflammatory and immunomodulatory properties, shows promise in mitigating UC, yet its therapeutic and underlying mechanisms remain unclear. In this study, colitis was induced in mice by administering 2.5% (w/v) dextran sulfate sodium (DSS) solution for 7 days. Oral (25, 50, and 100 mg/kg) FN for 10 days significantly ameliorated colitis symptoms in a dose-dependent manner, by mitigating body weight loss, reducing disease activity index (DAI), colonic weight, and colonic weight index, while enhancing survival rates and colonic length. Histological analysis revealed FN remarkably suppressed inflammatory damage in colonic tissues. Furthermore, FN modulated the expression of pro- and anti-inflammatory cytokines and enhanced antioxidant capacity. Notably, FN treatment significantly enhanced the expression of tight junction (TJ) proteins (claudin-1, ZO-1, occludin) at both protein and mRNA levels in the colon tissues, suggesting improved intestinal barrier function. Crucially, FN inhibited macrophage infiltration in colonic tissues and rebalanced M1/M2 macrophage polarization. While, macrophage depletion largely abrogated FN's protective effects against colitis, indicating a crucial role for macrophages in mediating FN's therapeutic response. Overall, FN effectively alleviated colitis primarily via modulating inflammatory cytokine expression, enhancing antioxidant capacity, upregulating TJs proteins expression, and remodeling M1/M2 macrophage polarization equilibrium. These findings suggest that FN could be the next candidate to unlocking UC's treatment challenge.

CAMs in command: aging brain macrophages fine-tune stroke immune responses

Central nervous system-associated macrophages (CAMs) are a unique subset of immune cells located at the interface between the blood and the brain parenchyma. In a recent study in mice, Levard and colleagues found that CAMs regulate immune cell trafficking, endothelial activation, and antigen presentation following stroke exclusively in aged animals, underscoring the importance of using translationally relevant models for studying age-related diseases.

Progesterone promotes CXCl2-dependent vaginal neutrophil killing by activating cervical resident macrophage-neutrophil crosstalk

Vaginal infections in women of reproductive age represent a clinical dilemma with significant socioeconomic implications. The current understanding of mucosal immunity failure during early pathogenic invasions that allows the pathogen to grow and thrive is far from complete. Neutrophils infiltrate most tissues following circadian patterns as part of normal repair, regulation of microbiota, or immune surveillance and become more numerous after infection. Neutrophils are responsible for maintaining vaginal immunity. Specific to the vagina, neutrophils continuously infiltrate at high levels, although during ovulation, they retreat to avoid sperm damage and permit reproduction. Here we show that, after ovulation, progesterone promotes resident vaginal macrophage-neutrophil crosstalk by upregulating Yolk sac early fetal organs (FOLR2+) macrophage CXCl2 expression, in a TNFA-patrolling monocyte-derived macrophage-mediated (CX3CR1hiMHCIIhi-mediated) manner, to activate the neutrophils' capacity to eliminate sex-transmitted and opportunistic microorganisms. Indeed, progesterone plays an essential role in conciliating the balance between the commensal microbiota, sperm, and the threat of pathogens because progesterone not only promotes a flurry of neutrophils but also increases neutrophilic fury to restore immunity after ovulation to thwart pathogenic invasion after intercourse. Therefore, modest progesterone dysregulations could lead to a suboptimal neutrophilic response, resulting in insufficient mucosal defense and recurrent unresolved infections.

Cardiac resident macrophages: Spatiotemporal distribution, development, physiological functions, and their translational potential on cardiac diseases

Cardiac resident macrophages (CRMs) are the main population of cardiac immune cells. The role of these cells in regeneration, functional remodeling, and repair after cardiac injury is always the focus of research. However, in recent years, their dynamic changes and contributions in physiological states have a significant attention. CRMs have specific phenotypes and functions in different cardiac chambers or locations of the heart and at different stages. They further show specific differentiation and development processes. The present review will summarize the new progress about the spatiotemporal distribution, potential developmental regulation, and their roles in cardiac development and aging as well as the translational potential of CRMs on cardiac diseases. Of course, the research tools for CRMs, their respective advantages and disadvantages, and key issues on CRMs will further be discussed.

Macrophage and monocyte subsets in response to ischemic stroke

Ischemic stroke is a leading cause of disability and mortality. Despite extensive efforts in stroke research, the only pharmacological treatment currently available is arterial recanalization, which has limited efficacy only in the acute phase of stroke. The neuroinflammatory response to stroke is believed to provide a wider time window than recanalization and has therefore been proposed as an attractive therapeutic target. In this review, we provide an overview of recent advances in the understanding of cellular and molecular responses of distinct macrophage populations following stroke, which may offer potential targets for therapeutic interventions. Specifically, we discuss the role of local responders in neuroinflammation, including the well-studied microglia as well as the emerging players, border-associated macrophages, and macrophages originating from the skull bone marrow. Additionally, we focus on the behavior of monocytes stemming from distant tissues such as the bone marrow and spleen. Finally, we highlight aging as a crucial factor modulating the immune response, which is often neglected in animal studies.