New Insights Into Tissue Macrophages: From Their Origin to the Development of Memory

The role of infection in signalling root resorption: A narrative review

BACKGROUND

Root resorption consists of complex, multistep processes that involve cell signalling caused by inflammation and stromal cells, which promotes the secretion of receptor activator of nuclear factor κB ligand/ macrophage-colony stimulating factor (RANKL/M-CSF) resulting in a resorptive process.

OBJECTIVE

The aim of this narrative review was to analyse the literature related to root resorption resulting from microbial infection and to comparing it with non-microbial infection.

METHODS

An electronic literature search was performed using the PubMed database and applying keywords of articles published in English. Eligible papers were reviewed to reveal the descriptions of bone and root resorption processes. The abstracts were searched manually to identify articles about infection-stimulating bone and root resorption.

RESULTS

Three main types of root resorption were identified, two associated with primary bacterial infection and one secondary to bacterial infection. These include external inflammatory resorption, internal inflammatory resorption and external cervical (invasive) resorption.

DISCUSSION

The magnitude of cytokine involvement that promotes resorption and M-CSF/RANKL production depends on multiple factors, including pathogen virulence, site of infection and host genetic factors that activate the inflammation at the infection site. Two mechanisms activate the resorption mechanisms-the canonical and non-canonical pathways that can activate clastic cells independently of the RANKL/RANK canonical pathways.

CONCLUSIONS

Two pathways of root resorption co-exist in the body. When resorption is caused by infection, chronic inflammation due to bacterial infection prolongs the secretions of pro-inflammatory cytokines that intensify root and bone resorption. The second pathway is bacterial independent of the non-infection root resorption that is part of the wound healing process, which is limited in time due to its innate ability.

Macrophage variants in laboratory research: most are well done, but some are RAW

Macrophages play a pivotal role in the innate immune response. While their most characteristic function is phagocytosis, it is important not to solely characterize macrophages by this activity. Their crucial roles in body development, homeostasis, repair, and immune responses against pathogens necessitate a broader understanding. Macrophages exhibit remarkable plasticity, allowing them to modify their functional characteristics in response to the tissue microenvironment (tissue type, presence of pathogens or inflammation, and specific signals from neighboring cells) swiftly. While there is no single defined "macrophage" entity, there is a diverse array of macrophage types because macrophage ontogeny involves the differentiation of progenitor cells into tissue-resident macrophages, as well as the recruitment and differentiation of circulating monocytes in response to tissue-specific cues. In addition, macrophages continuously sense and respond to environmental cues and tissue conditions, adjusting their functional and metabolic states accordingly. Consequently, it is of paramount importance to comprehend the heterogeneous origins and functions of macrophages employed in in vitro studies, as each available in vitro macrophage model is associated with specific sets of strengths and limitations. This review centers its attention on a comprehensive comparison between immortalized mouse macrophage cell lines and primary mouse macrophages. It provides a detailed analysis of the strengths and weaknesses inherent in these in vitro models. Finally, it explores the subtle distinctions between diverse macrophage cell lines, offering insights into numerous factors beyond the model type that can profoundly influence macrophage function.

Toward Systemic Lipofuscin Removal

Lipofuscin is indigestible garbage that accumulates in the autophagic vesicles and cytosol of postmitotic cells with age. Drs. Brunk and Terman postulated that lipofuscin accumulation is the main or at least a major driving factor in aging. They even posited that the evolution of memory is the reason why we get lipofuscin at all, as stable synaptic connections must be maintained over time, meaning that the somas of neurons must also remain in the same locale. In other words, they cannot dilute out their garbage over time through cell division. Mechanistically, their position certainly makes sense given that rendering a large percentage of a postmitotic cell's lysosomes useless must almost certainly negatively affect that cell and the surrounding microenvironment. It may be the case that lipofuscin accumulation is the main issue with regard to current age-related disease. Degradation in situ may be an insurmountable task currently. However, a method of systemic lipofuscin removal is discussed herein.

Monocytes and macrophages: Origin, homing, differentiation, and functionality during inflammation

Monocytes and macrophages are essential components of innate immune system and have versatile roles in homeostasis and immunity. These phenotypically distinguishable mononuclear phagocytes play distinct roles in different stages, contributing to the pathophysiology in various forms making them a potentially attractive therapeutic target in inflammatory conditions. Several pieces of evidence have supported the role of different cell surface receptors expressed on these cells and their downstream signaling molecules in initiating and perpetuating the inflammatory response. In this review, we discuss the current understanding of the monocyte and macrophage biology in inflammation, highlighting the role of chemoattractants, inflammasomes, and integrins in the function of monocytes and macrophages during events of inflammation. This review also covers the recent therapeutic interventions targeting these mononuclear phagocytes at the cellular and molecular levels.

Enhancement of Macrophage Immunity against Chlamydial Infection by Natural Killer T Cells

Lung macrophage (LM) is vital in host defence against bacterial infections. However, the influence of other innate immune cells on its function, including the polarisation of different subpopulations, remains poorly understood. This study examined the polarisation of LM subpopulations (monocytes/undifferentiated macrophages (Mo/Mφ), interstitial macrophages (IM), and alveolar macrophages (AM)). We further assessed the effect of invariant natural killer T cells (iNKT) on LM polarisation in a protective function against Chlamydia muridarum, an obligate intracellular bacterium, and respiratory tract infection. We found a preferentially increased local Mo/Mφ and IMs with a significant shift to a type-1 macrophage (M1) phenotype and higher expression of iNOS and TNF-α. Interestingly, during the same infection, the alteration of macrophage subpopulations and the shift towards M1 was much less in iNKT KO mice. More importantly, functional testing by adoptively transferring LMs isolated from iNKT KO mice (iNKT KO-Mφ) conferred less protection than those isolated from wild-type mice (WT-Mφ). Further analyses showed significantly reduced gene expression of the JAK/STAT signalling pathway molecules in iNKT KO-Mφ. The data show an important role of iNKT in promoting LM polarisation to the M1 direction, which is functionally relevant to host defence against a human intracellular bacterial infection. The alteration of JAK/STAT signalling molecule gene expression in iNKT KO-Mφ suggests the modulating effect of iNKT is likely through the JAK/STAT pathway.

Characterization of Hofbauer cell polarization and VEGF localization in human term placenta from active and inactive pregnant individuals

Physical activity (PA) during pregnancy is associated with parental and fetal health benefits; however, the mechanisms through which these benefits arise are yet to be fully understood. In healthy pregnancies Hofbauer cells (HBCs) comprise a heterogenous population containing CD206+ and CD206- phenotypes. In healthy pregnancies, CD206+ represent the majority, while dysregulations have been associated with pathological conditions. HBCs have also been identified as potential drivers of angiogenesis. As PA induces changes in macrophage polarization in non-pregnant populations, this novel study examined the relationship between PA and HBC polarization and to identify which HBC phenotypes express VEGF. Participants were classified as active or inactive, and immunofluorescence cell-labelling was used to quantify total HBCs, CD206+ HBCs, and the proportion of total HBCs expressing CD206. Immunofluorescent colocalization assessed which phenotypes expressed VEGF. Protein and mRNA expression of CD68 and CD206 were measured in term placenta tissue using Western blot and RT-qPCR, respectively. Both CD206+ and CD206- HBCs expressed VEGF. The proportion of CD206+ HBCs was elevated in active individuals; however, CD206 protein expression was observed to be lower in active participants. Combined with a lack of significant differences in CD206 mRNA levels, these findings suggest potential PA-mediated responses in HBC polarization and CD206 translational regulation.

Molecular Imaging of Innate Immunity and Immunotherapy

The innate immune system plays a key role as the first line of defense in various human diseases including cancer, cardiovascular and inflammatory diseases. In contrast to tissue biopsies and blood biopsies, in vivo imaging of the innate immune system can provide whole body measurements of immune cell location and function and changes in response to disease progression and therapy. Rationally developed molecular imaging strategies can be used in evaluating the status and spatio-temporal distributions of the innate immune cells in near real-time, mapping the biodistribution of novel innate immunotherapies, monitoring their efficacy and potential toxicities, and eventually for stratifying patients that are likely to benefit from these immunotherapies. In this review, we will highlight the current state-of-the-art in noninvasive imaging techniques for preclinical imaging of the innate immune system particularly focusing on cell trafficking, biodistribution, as well as pharmacokinetics and dynamics of promising immunotherapies in cancer and other diseases; discuss the unmet needs and current challenges in integrating imaging modalities and immunology and suggest potential solutions to overcome these barriers.

Optimal low-intensity pulsed ultrasound stimulation for promoting anti-inflammatory effects in macrophages

In this paper, we stimulated M1-like macrophages (obtained from U937 cells) with low-intensity pulsed ultrasound (LIPUS) to lower pro-inflammatory cytokine production. A systematic screening of different frequencies, intensities, duty cycles, and exposure times was performed. The optimal stimulation conditions leading to a marked decrease in the release of inflammatory cytokines were determined to be 38 kHz, 250 mW/cm², 20%, and 90 min, respectively. Using these parameters, we verified that up to 72 h LIPUS did not affect cell viability, resulting in an increase in metabolic activity and in a reduction of reactive oxygen species (ROS) production. Moreover, we found that two mechanosensitive ion channels (PIEZO1 and TRPV1) were involved in the LIPUS-mediated cytokine release modulation. We also assessed the role of the nuclear factor κB (NF-κB) signaling pathway and observed an enhancement of actin polymerization. Finally, transcriptomic data suggested that the bioeffects of LIPUS treatment occur through the modulation of p38 MAPK signaling pathway.

Specialized pro-resolving lipid mediators regulate inflammatory macrophages: A paradigm shift from antibiotics to immunotherapy for mitigating COVID-19 pandemic

The most severe clinical manifestations of the horrifying COVID-19 disease, that claimed millions of lives during the pandemic time, were Acute respiratory distress syndrome (ARDS), Coagulopathies, septic shock leading eventually to death. ARDS was a consequence of Cytokine storm. The viral SARS-COV2infection lead to avalanche of cytokines and eicosanoids causing "cytokine storm" and "eicosanoid storm." Cytokine storm is one of the macrophage-derived inflammatory responses triggered by binding of virus particles to ACE2 receptors of alveolar macrophages, arise mainly due to over production of various pro-inflammatory mediators like cytokines, e.g., interleukin (IL)-1, IL-2, and tumor necrosis factor (TNF)- α, causing pulmonary edema, acute respiratory distress, and multi-organ failure. Cytokine storm was regarded as the predictor of severity of the disease and was deemed one of the causes of the high mortality rates due to the COVID-19. The basis of cytokine storm is imbalanced switching between an inflammation increasing - pro-inflammatory (M1) and an inflammation regulating-anti-inflammatory (M2) forms of alveolar macrophages which further deteriorates if opportunistic secondary bacterial infections prevail in the lungs. Lack of sufficient knowledge regarding the virus and its influence on co-morbidities, clinical treatment of the diseases included exorbitant use of antibiotics to mitigate secondary bacterial infections, which led to the unwarranted development of multidrug resistance (MDR) among the population across the globe. Antimicrobial resistance (AMR) needs to be addressed from various perspectives as it may deprive future generations of the basic health immunity. Specialized pro-resolving mediators (SPMs) are generated from the stereoselective enzymatic conversions of essential fatty acids that serve as immune resolvents in controlling acute inflammatory responses. SPMs facilitate the clearance of injured tissue and cell debris, the removal of pathogens, and augment the concentration of anti-inflammatory lipid mediators. The SPMs, e.g., lipoxins, protectins, and resolvins have been implicated in exerting inhibitory influence on with cytokine storm. Experimental evidence suggests that SPMS lower antibiotic requirement. Therefore, in this review potential roles of SPMs in enhancing macrophage polarization, triggering immunological functions, hastening inflammation resolution, subsiding cytokine storm and decreasing antibiotic requirement that can reduce AMR load are discussed.

Superoxide Anion Chemistry-Its Role at the Core of the Innate Immunity

Classically, superoxide anion O2•- and reactive oxygen species ROS play a dual role. At the physiological balance level, they are a by-product of O2 reduction, necessary for cell signalling, and at the pathological level they are considered harmful, as they can induce disease and apoptosis, necrosis, ferroptosis, pyroptosis and autophagic cell death. This revision focuses on understanding the main characteristics of the superoxide O2•-, its generation pathways, the biomolecules it oxidizes and how it may contribute to their modification and toxicity. The role of superoxide dismutase, the enzyme responsible for the removal of most of the superoxide produced in living organisms, is studied. At the same time, the toxicity induced by superoxide and derived radicals is beneficial in the oxidative death of microbial pathogens, which are subsequently engulfed by specialized immune cells, such as neutrophils or macrophages, during the activation of innate immunity. Ultimately, this review describes in some depth the chemistry related to O2•- and how it is harnessed by the innate immune system to produce lysis of microbial agents.

Receptors of immune cells mediates recognition for tumors

Over the last few decades, the immune system has been steered toward eradication of cancer cells with the help of cancer immunotherapy. T cells, B cells, monocytes/macrophages, dendritic cells, T-reg cells, and natural killer (NK) cells are some of the numerous immune cell types that play a significant part in cancer cell detection and reduction of inflammation, and the antitumor response. Briefly stated, chimeric antigen receptors, adoptive transfer and immune checkpoint modulators are currently the subjects of research focus for successful immunotherapy-based treatments for a variety of cancers. This chapter discusses ongoing investigations on the mechanisms and recent developments by which receptors of immune cells especially that of lymphocytes and monocytes/macrophages regulate the detection of immune system leading to malignancies. We will also be looking into the treatment strategies based on these mechanisms.

Innate Immune Memory in Macrophages

Macrophages have been recognized as the primary mediators of innate immunity starting from embryonic/fetal development. Macrophage-mediated defenses may not be as antigen-specific as adaptive immunity, but increasing information suggests that these responses do strengthen with repeated immunological triggers. The concept of innate memory in macrophages has been described as "trained immunity" or "innate immune memory (IIM)." As currently understood, this cellular memory is rooted in epigenetic and metabolic reprogramming. The recognition of IIM may be particularly important in the fetus and the young neonate who are yet to develop protective levels of adaptive immunity, and could even be of preventive/therapeutic importance in many disorders. There may also be a possibility of therapeutic enhancement with targeted vaccination. This article presents a review of the properties, mechanisms, and possible clinical significance of macrophage-mediated IIM.

Extract of Pinus densiflora needles suppresses acute inflammation by regulating inflammatory mediators in RAW264.7 macrophages and mice

CONTEXT

Pinus densiflora Siebold & Zucc. (Pinaceae) needle extracts ameliorate oxidative stress, but research into their anti-inflammatory effects is limited.

OBJECTIVE

To investigate antioxidant and anti-inflammatory effects of a Pinus densiflora needles (PINE) ethanol extract in vitro and in vivo.

MATERIALS AND METHODS

We measured levels of reactive oxygen species (ROS), superoxide dismutase (SOD) and inflammatory mediators in lipopolysaccharide (LPS)-stimulated RAW264.7 cells at various PINE concentrations (25, 50 and 100 μg/mL; but 6.25, 12.5 and 25 μg/mL for interleukin-1β and prostaglandin E₂ (PGE₂)). Thirty ICR mice were randomized to six groups: vehicle, control, PINE pre-treatment (0.1, 0.3 and 1 mg/left ear for 10 min followed by arachidonic acid treatment for 30 min) and dexamethasone. The posttreatment ear thickness and myeloperoxidase (MPO) activity were measured.

RESULTS

PINE 100 μg/mL significantly decreased ROS (IC₅₀, 70.93 μg/mL, p < 0.01), SOD (IC₅₀, 30.99 μg/mL, p < 0.05), malondialdehyde (p < 0.01), nitric oxide (NO) (IC₅₀, 27.44 μg/mL, p < 0.01) and tumour necrosis factor-alpha (p < 0.05) levels. Interleukin-1β (p < 0.05) and PGE₂ (p < 0.01) release decreased significantly with 25 μg/mL PINE. PINE 1 mg/ear inhibited LPS-stimulated expression of cyclooxygenase-2 and inducible NO synthase in RAW264.7 macrophages and significantly inhibited ear oedema (36.73-15.04% compared to the control, p < 0.01) and MPO activity (167.94-105.59%, p < 0.05).

DISCUSSION AND CONCLUSIONS

PINE exerts antioxidant and anti-inflammatory effects by inhibiting the production of inflammatory mediators. Identified flavonoids such as taxifolin and quercetin glucoside can be attributed to effect of PINE.

New Iron Metabolic Pathways and Chelation Targeting Strategies Affecting the Treatment of All Types and Stages of Cancer

There is new and increasing evidence from in vitro, in vivo and clinical studies implicating the pivotal role of iron and associated metabolic pathways in the initiation, progression and development of cancer and in cancer metastasis. New metabolic and toxicity mechanisms and pathways, as well as genomic, transcription and other factors, have been linked to cancer and many are related to iron. Accordingly, a number of new targets for iron chelators have been identified and characterized in new anticancer strategies, in addition to the classical restriction of/reduction in iron supply, the inhibition of transferrin iron delivery, the inhibition of ribonucleotide reductase in DNA synthesis and high antioxidant potential. The new targets include the removal of excess iron from iron-laden macrophages, which affects anticancer activity; the modulation of ferroptosis; ferritin iron removal and the control of hyperferritinemia; the inhibition of hypoxia related to the role of hypoxia-inducible factor (HIF); modulation of the function of new molecular species such as STEAP4 metalloreductase and the metastasis suppressor N-MYC downstream-regulated gene-1 (NDRG1); modulation of the metabolic pathways of oxidative stress damage affecting mitochondrial function, etc. Many of these new, but also previously known associated iron metabolic pathways appear to affect all stages of cancer, as well as metastasis and drug resistance. Iron-chelating drugs and especially deferiprone (L1), has been shown in many recent studies to fulfill the role of multi-target anticancer drug linked to the above and also other iron targets, and has been proposed for phase II trials in cancer patients. In contrast, lipophilic chelators and their iron complexes are proposed for the induction of ferroptosis in some refractory or recurring tumors in drug resistance and metastasis where effective treatments are absent. There is a need to readdress cancer therapy and include therapeutic strategies targeting multifactorial processes, including the application of multi-targeting drugs involving iron chelators and iron-chelator complexes. New therapeutic protocols including drug combinations with L1 and other chelating drugs could increase anticancer activity, decrease drug resistance and metastasis, improve treatments, reduce toxicity and increase overall survival in cancer patients.

Roles of Altered Macrophages and Cytokines: Implications for Pathological Mechanisms of Postmenopausal Osteoporosis, Rheumatoid Arthritis, and Alzheimer's Disease

Postmenopausal osteoporosis (PMOP) is characterized by the uncoupling of bone resorption and bone formation induced by estrogen deficiency, which is a complex outcome related to estrogen and the immune system. The interaction between bone and immune cells is regarded as the context of PMOP. Macrophages act differently on bone cells, depending on their polarization profile and secreted paracrine factors, which may have implications for the development of PMOP. PMOP, rheumatoid arthritis (RA), and Alzheimer's disease (AD) might have pathophysiological links, and the similarity of their pathological mechanisms is partially visible in altered macrophages and cytokines in the immune system. This review focuses on exploring the pathological mechanisms of PMOP, RA, and AD through the roles of altered macrophages and cytokines secretion. First, the multiple effects on cytokines secretion by bone-bone marrow (BM) macrophages in the pathological mechanism of PMOP are reviewed. Then, based on the thought of "different tissue-same cell type-common pathological molecules-disease pathological links-drug targets" and the methodologies of "molecular network" in bioinformatics, highlight that multiple cytokines overlap in the pathological molecules associated with PMOP vs. RA and PMOP vs. AD, and propose that these overlaps may lead to a pathological synergy in PMOP, RA, and AD. It provides a novel strategy for understanding the pathogenesis of PMOP and potential drug targets for the treatment of PMOP.

Resolving macrophage polarization through distinct Ca2+ entry channel that maintains intracellular signaling and mitochondrial bioenergetics

Transformation of naive macrophages into classically (M1) or alternatively (M2) activated macrophages regulates the inflammatory response. Here, we identified that distinct Ca2+ entry channels determine the IFNγ-induced M1 or IL-4-induced M2 transition. Naive or M2 macrophages exhibit a robust Ca2+ entry that was dependent on Orai1 channels, whereas the M1 phenotype showed a non-selective TRPC1 current. Blockade of Ca2+ entry suppresses pNF-κB/pJNK/STAT1 or STAT6 signaling events and consequently lowers cytokine production that is essential for M1 or M2 functions. Of importance, LPS stimulation shifted M2 cells from Orai1 toward TRPC1-mediated Ca2+ entry and TRPC1-/- mice exhibited transcriptional changes that suppress pro-inflammatory cytokines. In contrast, Orai1-/- macrophages showed a decrease in anti-inflammatory cytokines and exhibited a suppression of mitochondrial oxygen consumption rate and inhibited mitochondrial shape transition specifically in the M2 cells. Finally, alterations in TRPC1 or Orai1 expression determine macrophage polarization suggesting a distinct role of Ca2+ channels in modulating macrophage transformation.

The Gut-Liver Axis in Chronic Liver Disease: A Macrophage Perspective

Chronic liver disease (CLD) is a growing health concern which accounts for two million deaths per year. Obesity, alcohol overconsumption, and progressive cholestasis are commonly characterized by persistent low-grade inflammation and advancing fibrosis, which form the basis for development of end-stage liver disease complications, including hepatocellular carcinoma. CLD pathophysiology extends to the intestinal tract and is characterized by intestinal dysbiosis, bile acid dysregulation, and gut barrier disruption. In addition, macrophages are key players in CLD progression and intestinal barrier breakdown. Emerging studies are unveiling macrophage heterogeneity and driving factors of their plasticity in health and disease. To date, in-depth investigation of how gut-liver axis disruption impacts the hepatic and intestinal macrophage pool in CLD pathogenesis is scarce. In this review, we give an overview of the role of intestinal and hepatic macrophages in homeostasis and gut-liver axis disruption in progressive stages of CLD.

Functionalized Nanoparticles Targeting Tumor-Associated Macrophages as Cancer Therapy

The tumor microenvironment (TME) plays a central role in regulating antitumor immune responses. As an important part of the TME, alternatively activated type 2 (M2) macrophages drive the development of primary and secondary tumors by promoting tumor cell proliferation, tumor angiogenesis, extracellular matrix remodeling and overall immunosuppression. Immunotherapy approaches targeting tumor-associated macrophages (TAMs) in order to reduce the immunosuppressive state in the TME have received great attention. Although these methods hold great potential for the treatment of several cancers, they also face some limitations, such as the fast degradation rate of drugs and drug-induced cytotoxicity of organs and tissues. Nanomedicine formulations that prevent TAM signaling and recruitment to the TME or deplete M2 TAMs to reduce tumor growth and metastasis represent encouraging novel strategies in cancer therapy. They allow the specific delivery of antitumor drugs to the tumor area, thereby reducing side effects associated with systemic application. In this review, we give an overview of TAM biology and the current state of nanomedicines that target M2 macrophages in the course of cancer immunotherapy, with a specific focus on nanoparticles (NPs). We summarize how different types of NPs target M2 TAMs, and how the physicochemical properties of NPs (size, shape, charge and targeting ligands) influence NP uptake by TAMs in vitro and in vivo in the TME. Furthermore, we provide a comparative analysis of passive and active NP-based TAM-targeting strategies and discuss their therapeutic potential.

Hypertrophic Scarring: Current Knowledge of Predisposing Factors, Cellular and Molecular Mechanisms

Hypertrophic scarring (HSc) is an age-old problem that still affects millions of people physically, psychologically, and economically. Despite advances in surgical techniques and wound care, prevention and treatment of HSc remains a challenge. Elucidation of factors involved in the development of this common fibroproliferative disorder is crucial for further progress in preventive and/or therapeutic measures. Our knowledge about pathophysiology of HSc at the cellular and molecular level has grown considerably in recent decades. In this article, current knowledge of predisposing factors and the cellular and molecular mechanisms of HSc has been reviewed.

Glucose Metabolism: The Metabolic Signature of Tumor Associated Macrophage

Macrophages exist in most tissues of the body, where they perform various functions at the same time equilibrating with other cells to maintain immune responses in numerous diseases including cancer. Recently, emerging investigations revealed that metabolism profiles control macrophage phenotypes and functions, and in turn, polarization can trigger metabolic shifts in macrophages. Those findings implicate a special role of metabolism in tumor-associated macrophages (TAMs) because of the sophisticated microenvironment in cancer. Glucose is the major energy source of cells, especially for TAMs. However, the complicated association between TAMs and their glucose metabolism is still unclearly illustrated. Here, we review the recent advances in macrophage and glucose metabolism within the tumor microenvironment, and the significant transformations that occur in TAMs during the tumor progression. Additionally, we have also outlined the potential implications for macrophage-based therapies in cancer targeting TAMs.

Cord-Blood-Derived Professional Antigen-Presenting Cells: Functions and Applications in Current and Prospective Cell Therapies

Human umbilical cord blood (UCB) represents a valuable source of hematopoietic stem cells, particularly for patients lacking a matching donor. UCB provides practical advantages, including a lower risk of graft-versus-host-disease and permissive human leukocyte antigen mismatching. These advantageous properties have so far been applied for stem cell, mesenchymal stromal cell, and chimeric antigen receptor T cell therapies. However, UCB-derived professional antigen-presenting cells are increasingly being utilized in the context of immune tolerance and regenerative therapy. Here, we review the cell-specific characteristics as well as recent advancements in UCB-based cell therapies focusing on dendritic cells, monocytes, B lymphocytes, innate lymphoid cells, and macrophages.

Phenotypic Switch of Human Peritoneal Macrophages during Childhood

INTRODUCTION

 Human peritoneal macrophages are resident in the abdominal cavity where they support the specific microenvironmental regulation. We have previously observed a phenotypic switch of murine macrophages during infancy that was associated with a functional development. To investigate the age related changes in human peritoneal macrophages, we analyzed peritoneal macrophages of children undergoing laparoscopic procedures.

MATERIALS AND METHODS

 Immunologically healthy children who received minimally invasive surgery in our department were included in this study. In all cases, the written consent was obtained. At the beginning of laparoscopy, physiologic NaCl-solution was instilled and manually removed through the umbilical trocar to gain macrophages. Lavage cells were processed for flow cytometry analysis. CD14+ myeloid cells were monitored for specific lineage marker expression.

RESULTS

 A total of 21 donors (age: 7 days-18 years) were included and divided into three groups. In all age groups, 97% of myeloid cells expressed CD11b. 70% of these expressed CD14. Three subsets of CD14 cells were detected on the basis of CD14/CD16 expression (CD14 + CD16dim, CD14 + CD16inter, and CD14 + CD16high). In neonates, >80% belonged to the CD14 + CD16high subset, reducing to 30% in adolescents. In none of the cases, the M2 markers CD23 and CD25 were expressed.

CONCLUSION

 This is the first study showing that lineage marker expression of peritoneal macrophages in neonates differs from that in adults. The knowledge about neonatal tissue resident macrophages might help to understand their complex interaction and to use specific macrophage properties for therapeutic approaches.

Importance of Deubiquitination in Macrophage-Mediated Viral Response and Inflammation

Ubiquitination and deubiquitination play a fundamental role in the signaling pathways associated with innate and adaptive immune responses. Macrophages are key sentinels for the host defense, triggering antiviral and inflammatory responses against various invading pathogens. Macrophages recognize the genetic material of these pathogens as pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) through the activation of its pattern recognition receptors (PRRs), initiating the cascade of immune signaling, which leads to the production of pro- and anti-inflammatory cytokines that initiates the appropriate immune response. Macrophage-mediated immune response is highly regulated and tightly controlled by the ubiquitin system since its abnormal activation or dysregulation may result in the severe pathogenesis of numerous inflammatory and autoimmune diseases. Deubiquitinating enzymes (DUBs) play a crucial role in reversing the ubiquitination and controlling the magnitude of the immune response. During infection, pathogens manipulate the host defense system by regulating DUBs to obtain nutrients and increase proliferation. Indeed, the regulation of DUBs by small molecule inhibitors has been proposed as an excellent way to control aberrant activation of immune signaling molecules. This review is focused on the complex role of DUBs in macrophage-mediated immune response, exploring the potential use of DUBs as therapeutic targets in autoimmune and inflammatory diseases by virtue of small molecule DUB inhibitors.

Gold Nanoparticles Modulate BCG-Induced Innate Immune Memory in Human Monocytes by Shifting the Memory Response towards Tolerance

Innate immune memory is characterized by a modulation in the magnitude with which innate immune cells such as monocytes and macrophages respond to potential dangers, subsequent to previous exposure to the same or unrelated agents. In this study, we have examined the capacity of gold nanoparticles (AuNP), which are already in use for therapeutic and diagnostic purposes, to modulate the innate memory induced by bacterial agents. The induction of innate memory was achieved in vitro by exposing human primary monocytes to bacterial agents (lipopolysaccharide -LPS-, or live Bacille Calmette-Guérin -BCG) in the absence or presence of AuNP. After the primary activation, cells were allowed to return to a resting condition, and eventually re-challenged with LPS. The induction of memory was assessed by comparing the response to the LPS challenge of unprimed cells with that of cells primed with bacterial agents and AuNP. The response to LPS was measured as the production of inflammatory (TNFα, IL-6) and anti-inflammatory cytokines (IL-10, IL-1Ra). While ineffective in directly inducing innate memory per se, and unable to influence LPS-induced tolerance memory, AuNP significantly affected the memory response of BCG-primed cells, by inhibiting the secondary response in terms of both inflammatory and anti-inflammatory factor production. The reprogramming of BCG-induced memory towards a tolerance type of reactivity may open promising perspectives for the use of AuNP in immunomodulatory approaches to autoimmune and chronic inflammatory diseases.

Serum levels of the chemokine CCL2 are elevated in malignant pleural mesothelioma patients

BACKGROUND

Malignant pleural mesothelioma (MPM) is a debilitating disease of the pleural cavity. It is primarily associated with previous inhalation of asbestos fibers. These fibers initiate an oxidant coupled inflammatory response. Repeated exposure to asbestos fibers results in a prolonged inflammatory response and cycles of tissue damage and repair. The inflammation-associated cycles of tissue damage and repair are intimately involved in the development of asbestos-associated cancers. Macrophages are a key component of asbestos-associated inflammation and play essential roles in the etiology of a variety of cancers. Macrophages are also a source of C-C motif chemokine ligand 2 (CCL2), and a variety of tumor-types express CCL2. High levels of CCL2 are present in the pleural effusions of mesothelioma patients, however, CCL2 has not been examined in the serum of mesothelioma patients.

METHODS

The present study was carried out with 50 MPM patients and 356 subjects who were possibly exposed to asbestos but did not have disease symptoms and 41 healthy volunteers without a history of exposure to asbestos. The levels of CCL2 in the serum of the study participants was determined using ELISA.

RESULTS

Levels of CCL2 were significantly elevated in the serum of patients with advanced MPM.

CONCLUSIONS

Our findings are consistent with the premise that the CCL2/CCR2 axis and myeloid-derived cells play an important role in MPM and disease progression. Therapies are being developed that target CCL2/CCR2 and tumor resident myeloid cells, and clinical trials are being pursued that use these therapies as part of the treatment regimen. The results of trials with patients with a similar serum CCL2 pattern as MPM patients will have important implications for the treatment of MPM.

Macrophage PPAR-γ suppresses long-term lung fibrotic sequelae following acute influenza infection

Influenza virus causes a heterogeneous respiratory infectious disease ranging from self-limiting symptoms to non-resolving pathology in the lungs. Worldwide, seasonal influenza infections claim ~500,000 lives annually. Recent reports describe pathologic pulmonary sequelae that result in remodeling the architecture of lung parenchyma following respiratory infections. These dysfunctional recovery processes that disproportionately impact the elderly have been understudied. Macrophages are involved in tissue remodeling and are critical for survival of severe influenza infection. Here, we found intrinsic deficiency of the nuclear receptor PPAR-γ in myeloid cells delayed the resolution of pulmonary inflammation following influenza infection. Mice with myeloid cell-specific PPAR-γ deficiency subsequently presented with increased influenza-induced deposition of pulmonary collagen compared to control mice. This dysfunctional lung remodeling was progressive and sustained for at least 3 months following infection of mice with myeloid PPAR-γ deficiency. These progressive changes were accompanied by a pro-fibrotic gene signature from lung macrophages and preceded by deficiencies in activation of genes involved with damage repair. Importantly similar aberrant gene expression patterns were also found in a secondary analysis of a study where macrophages were isolated from patients with fibrotic interstitial lung disease. Quite unexpectedly, mice with PPAR-γ deficient macrophages were more resistant to bleomycin-induced weight loss whereas extracellular matrix deposition was unaffected compared to controls. Therefore PPAR-γ expression in macrophages may be a pathogen-specific limiter of organ recovery rather than a ubiquitous effector pathway in response to generic damage.

The role of macrophages during acute kidney injury: destruction and repair

Acute kidney injury (AKI) is defined by a rapid decline in renal function. Regardless of the initial cause of injury, the influx of immune cells is a common theme during AKI. While an inflammatory response is critical for the initial control of injury, a prolonged response can negatively affect tissue repair. In this review, we focus on the role of macrophages, from early inflammation to resolution, during AKI. These cells serve as the innate defense system by phagocytosing cellular debris and pathogenic molecules and bridge communication with the adaptive immune system by acting as antigen-presenting cells and secreting cytokines. While many immune cells function to initiate inflammation, macrophages play a complex role throughout AKI. This complexity is driven by their functional plasticity: the ability to polarize from a "pro-inflammatory" phenotype to a "pro-reparative" phenotype. Importantly, experimental and translational studies indicate that macrophage polarization opens the possibility to generate novel therapeutics to promote repair during AKI. A thorough understanding of the biological roles these phagocytes play during both injury and repair is necessary to understand the limitations while furthering the therapeutic application.

Roles of Ceramides and Other Sphingolipids in Immune Cell Function and Inflammation

Ceramides are bioactive sphingolipids that support the structure of the plasma membrane and mediate numerous cell-signaling events in eukaryotic cells. The finding that ceramides act as second messengers transducing cellular signals has attracted substantial attention in several fields of Biology. Since all cells contain lipid plasma membranes, the impact of various ceramides, ceramide synthases, ceramide metabolites, and other sphingolipids has been implicated in a vast range of cellular functions including, migration, proliferation, response to external stimuli, and death. The roles of lipids in these functions widely differ among the diverse cell types. Herein, we discuss the roles of ceramides and other sphingolipids in mediating the function of various immune cells; particularly dendritic cells, neutrophils, and macrophages. In addition, we highlight the main studies describing effects of ceramides in inflammation, specifically in various inflammatory settings including insulin resistance, graft-versus-host disease, immune suppression in cancer, multiple sclerosis, and inflammatory bowel disease.

Beneficial or Harmful Role of Macrophages in Guillain-Barré Syndrome and Experimental Autoimmune Neuritis

Guillain-Barré syndrome (GBS), an immune-mediated demyelinating peripheral neuropathy, is characterized by acute weakness of the extremities and areflexia or hyporeflexia. Experimental autoimmune neuritis (EAN) is a common animal model for GBS, which represents a CD4+ T cell-mediated inflammatory autoimmune demyelination of the peripheral nervous system (PNS), and is used to investigate the pathogenic mechanism of GBS. It has been found that macrophages play a critical role in the pathogenesis of both GBS and EAN. Macrophages have been primarily classified into two major phenotypes: proinflammatory macrophages (M1) and anti-inflammatory macrophages (M2). The two different macrophage subsets M1 and M2 may play a decisive role in initiation and development of GBS and EAN. However, recently, it has been indicated that the roles of macrophages in immune regulation and autoimmune diseases are more complex than those suggested by a simple M1-M2 dichotomy. Macrophages might exert either inflammatory or anti-inflammatory effect by secreting pro- or anti-inflammatory cytokines, and either inducing the activation of T cells to mediate immune response, resulting in inflammation and demyelination in the PNS, or promoting disease recovery. In this review, we summarize the dual roles of macrophages in GBS and EAN and explore the mechanism of macrophage polarization to provide a potential therapeutic approach for GBS in the future.

Beneficial or Harmful Role of Macrophages in Guillain-Barré Syndrome and Experimental Autoimmune Neuritis

Guillain-Barré syndrome (GBS), an immune-mediated demyelinating peripheral neuropathy, is characterized by acute weakness of the extremities and areflexia or hyporeflexia. Experimental autoimmune neuritis (EAN) is a common animal model for GBS, which represents a CD4⁺ T cell-mediated inflammatory autoimmune demyelination of the peripheral nervous system (PNS), and is used to investigate the pathogenic mechanism of GBS. It has been found that macrophages play a critical role in the pathogenesis of both GBS and EAN. Macrophages have been primarily classified into two major phenotypes: proinflammatory macrophages (M1) and anti-inflammatory macrophages (M2). The two different macrophage subsets M1 and M2 may play a decisive role in initiation and development of GBS and EAN. However, recently, it has been indicated that the roles of macrophages in immune regulation and autoimmune diseases are more complex than those suggested by a simple M1-M2 dichotomy. Macrophages might exert either inflammatory or anti-inflammatory effect by secreting pro- or anti-inflammatory cytokines, and either inducing the activation of T cells to mediate immune response, resulting in inflammation and demyelination in the PNS, or promoting disease recovery. In this review, we summarize the dual roles of macrophages in GBS and EAN and explore the mechanism of macrophage polarization to provide a potential therapeutic approach for GBS in the future.

Beneficial or Harmful Role of Macrophages in Guillain-Barré Syndrome and Experimental Autoimmune Neuritis

Guillain-Barré syndrome (GBS), an immune-mediated demyelinating peripheral neuropathy, is characterized by acute weakness of the extremities and areflexia or hyporeflexia. Experimental autoimmune neuritis (EAN) is a common animal model for GBS, which represents a CD4⁺ T cell-mediated inflammatory autoimmune demyelination of the peripheral nervous system (PNS), and is used to investigate the pathogenic mechanism of GBS. It has been found that macrophages play a critical role in the pathogenesis of both GBS and EAN. Macrophages have been primarily classified into two major phenotypes: proinflammatory macrophages (M1) and anti-inflammatory macrophages (M2). The two different macrophage subsets M1 and M2 may play a decisive role in initiation and development of GBS and EAN. However, recently, it has been indicated that the roles of macrophages in immune regulation and autoimmune diseases are more complex than those suggested by a simple M1-M2 dichotomy. Macrophages might exert either inflammatory or anti-inflammatory effect by secreting pro- or anti-inflammatory cytokines, and either inducing the activation of T cells to mediate immune response, resulting in inflammation and demyelination in the PNS, or promoting disease recovery. In this review, we summarize the dual roles of macrophages in GBS and EAN and explore the mechanism of macrophage polarization to provide a potential therapeutic approach for GBS in the future.

Investigation of tumor-tumor interactions in a double human cervical carcinoma xenograft model in nude mice

Tumor-tumor distant interactions within one organism are of major clinical relevance determining clinical outcome. To investigate this poorly understood phenomenon, a double human cervical xenograft model in nude mice was developed. A first tumor was induced subcutaneously by injection of human papillomavirus positive cervical carcinoma cells into the mouse lower right flank and 3 weeks later, animals were challenged with the same tumor cell line injected subcutaneously into the upper left flank. These tumors had no direct physical contact and we found no systemic changes induced by the primary tumor affecting the growth of a secondary tumor. However, ablation of the primary tumor by local treatment with cidofovir, a nucleotide analogue with known antiviral and antiproliferative properties, resulted not only in a local antitumor effect but also in a temporary far-reaching effect leading to retarded growth of the challenged tumor. Cidofovir far-reaching effects were linked to a reduced tumor-driven inflammation, to increased anti-tumor immune responses, and could not be enhanced by co-administration with immune stimulating adjuvants. Our findings point to the potential use of cidofovir in novel therapeutic strategies aiming to kill tumor cells as well as to influence the immune system to fight cancer.

The influence of vitamin D on M1 and M2 macrophages in patients with Crohn's disease

Defective bacterial clearance by macrophages plays an important role in Crohn's disease (CD). Phenotypes and functions of inflammatory M1 and anti-inflammatory M2 have not been studied in CD. Vitamin D supplementation reduces the severity of CD by unclear mechanisms. We studied macrophage characteristics in CD and controls and the effects of 1,25 vitamin D (1,25D). PBMC were isolated from CD patients and controls. M1 and M2 were generated by culturing of monocytes with GM-CSF and M-CSF, respectively. CD M1 and M2 showed normal phagocytosis and chemotaxis to CCL2 and fMLP. LPS-induced production of TNF-α, IL-12p40 and IL-10 was comparable between groups. Phagocytosis was unaltered with 1,25D; migration only increased marginally. M1 produced more IL-12p40 and TNF-α; IL-10 was greater in M2. 1,25D markedly decreased IL-12p40 by M1 and M2. 1,25D decreased TNF-α in CD M1; IL-10 levels were unaffected. M2 express F13A1, PTGS2, CD163, CXCL10, CD14 and MMP2, whereas TGF-β, CCL1 and CYP27B1 expression was higher in M1. Marker expression was similar between CD and controls. M1 and M2 markers were not differentially modulated by 1,25D. CD macrophages are not functionally or phenotypically different vs.

CONTROLS

1,25D markedly decreased pro-inflammatory M1 cytokines but did not modulate polarization to anti-inflammatory M2 phenotype.

Pinus densiflora needle supercritical fluid extract suppresses the expression of pro-inflammatory mediators iNOS, IL-6 and IL-1β, and activation of inflammatory STAT1 and STAT3 signaling proteins in bacterial lipopolysaccharide-challenged murine macrophages

Background

Regulation of a persistently-activated inflammatory response in macrophages is an important target for treatment of various chronic diseases. Pine needle extracts are well known to have potent immunomodulatory effects. The current study was designed to evaluate the effects of Pinus densiflora needle supercritical fluid extract (PDN-SCFE) on bacterial lipopolysaccharide (LPS)-induced inflammatory response in RAW 264.7 murine macrophages.

Methods

Cytotoxic effect of PDN-SCFE was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The levels of nitric oxide (NO) and the corresponding enzyme, inducible nitric oxide synthase (iNOS), were quantified by Griess and immunoblotting methods, respectively. The levels of cytokines were quantified using commercial ELISA kits. Quantitative real-time PCR (qRT-PCR) analysis was performed to assess the mRNA expression of iNOS and cytokines. To elucidate the mechanism of action, the involvement of nuclear transcription factor-kappa B (NFκB), mitogen activated protein kinases (MAPKs) and Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathways were examined by an immunoblotting method. In addition, the cellular localization of NFκB was analyzed by immunofluorescence staining.

Results

MTT assay results indicated that PDN-SCFE is non-toxic to RAW 264.7 cells up to a maximum assayed concentration of 40 μg/mL. The PDN-SCFE exhibited a concentration-dependent inhibitory effect on LPS-induced NO production by down regulating the expression of iNOS. In addition, the extract suppressed the LPS-induced expression of interleukin-6 (IL-6) and interleukin-1β (IL-1β) but not tumour necrosis factor-α (TNFα). Mechanistic studies revealed that PDN-SCFE does not influence the NFκB and MAPK pathways. However, it showed a significant inhibitory effect on LPS-induced activation of STAT1 and STAT3 proteins in macrophages.

Conclusion

The present findings revealed that the anti-inflammatory activity of PDN-SCFE in LPS-challenged RAW 264.7 macrophages is probably caused by the suppression of the JAK-STAT signaling pathway.

Graphical Abstract

Localized Sympathectomy Reduces Mechanical Hypersensitivity by Restoring Normal Immune Homeostasis in Rat Models of Inflammatory Pain

Some forms of chronic pain are maintained or enhanced by activity in the sympathetic nervous system (SNS), but attempts to model this have yielded conflicting findings. The SNS has both pro- and anti-inflammatory effects on immunity, confounding the interpretation of experiments using global sympathectomy methods. We performed a "microsympathectomy" by cutting the ipsilateral gray rami where they entered the spinal nerves near the L4 and L5 DRG. This led to profound sustained reductions in pain behaviors induced by local DRG inflammation (a rat model of low back pain) and by a peripheral paw inflammation model. Effects of microsympathectomy were evident within one day, making it unlikely that blocking sympathetic sprouting in the local DRGs or hindpaw was the sole mechanism. Prior microsympathectomy greatly reduced hyperexcitability of sensory neurons induced by local DRG inflammation observed 4 d later. Microsympathectomy reduced local inflammation and macrophage density in the affected tissues (as indicated by paw swelling and histochemical staining). Cytokine profiling in locally inflamed DRG showed increases in pro-inflammatory Type 1 cytokines and decreases in the Type 2 cytokines present at baseline, changes that were mitigated by microsympathectomy. Microsympathectomy was also effective in reducing established pain behaviors in the local DRG inflammation model. We conclude that the effect of sympathetic fibers in the L4/L5 gray rami in these models is pro-inflammatory. This raises the possibility that therapeutic interventions targeting gray rami might be useful in some chronic inflammatory pain conditions.

SIGNIFICANCE STATEMENT

Sympathetic blockade is used for many pain conditions, but preclinical studies show both pro- and anti-nociceptive effects. The sympathetic nervous system also has both pro- and anti-inflammatory effects on immune tissues and cells. We examined effects of a very localized sympathectomy. By cutting the gray rami to the spinal nerves near the lumbar sensory ganglia, we avoided widespread sympathetic denervation. This procedure profoundly reduced mechanical pain behaviors induced by a back pain model and a model of peripheral inflammatory pain. One possible mechanism was reduction of inflammation in the sympathetically denervated regions. This raises the possibility that therapeutic interventions targeting gray rami might be useful in some inflammatory conditions.

Short-Term Alcohol Abstinence Improves Antibacterial Defenses of Chronic Alcohol-Consuming Mice against Gut Bacteria-Associated Sepsis Caused by Enterococcus faecalis Oral Infection

The effects of short-term alcohol abstinence on host antibacterial resistance against Enterococcus faecalis oral infection was investigated in chronic alcohol-consuming mice [mice with 0.1 g/day of 20% ethanol consumption for 12 or 16 weeks (CAC-mice)]. These mice were highly susceptible to the infection; however, after 7 days of alcohol abstinence (aaCAC-mice), their antibacterial resistances were completely restored to the normal mouse level. Normal mice inoculated with CAC-mouse hepatic macrophages were shown to be susceptible to the infection, whereas the same macrophage preparation from aaCAC-mice did not impair the antibacterial resistance of normal mice. aaCAC-mouse liver macrophages protected nonobese diabetic-severe combined immunodeficiency IL-2Rγ^null mice exposed to E. faecalis, whereas those from CAC-mice did not. Monocyte-derived (MD) M2b macrophages were predominantly isolated from CAC-mouse livers, but these cells were not significantly isolated from aaCAC-mouse livers. Hepatic MD macrophages from aaCAC-mice switched to M1 macrophages in response to bacterial antigen, whereas the same macrophage preparation from CAC-mice did not. M1 Kupffer cells, M2a Kupffer cells, and MD M2b macrophages were shown to be not bactericidal, whereas E. faecalis was killed effectively by M1 macrophages derived from aaCAC-mouse hepatic MD macrophages. These results indicate that MD M2b macrophages predominantly distributed in the liver are responsible for the impaired resistance of CAC-mice to E. faecalis oral infection, and aaCAC-mice without MD M2b macrophages in the livers are resistant to the infection.

Syk Plays a Critical Role in the Expression and Activation of IRAK1 in LPS-Treated Macrophages

To address how interleukin-1 receptor-associated kinase 1 (IRAK1) is controlled by other enzymes activated by toll-like receptor (TLR) 4, we investigated the possibility that spleen tyrosine kinase (Syk), a protein tyrosine kinase that is activated at an earlier stage during TLR4 activation, plays a central role in regulating the functional activation of IRAK1. Indeed, we found that overexpression of myeloid differentiation primary response gene 88 (MyD88), an adaptor molecule that drives TLR signaling, induced IRAK1 expression and that piceatannol, a Syk inhibitor, successfully suppressed the MyD88-dependent upregulation of IRAK1 under LPS treatment conditions. Interestingly, in Syk-knockout RAW264.7 cells, IRAK1 activity was almost completely blocked after LPS treatment, while providing a Syk-recovery gene to the knockout cells successfully restored IRAK1 expression. According to our measurements of IRAK1 mRNA levels, the transcriptional upregulation of IRAK1 was induced by LPS treatment between 4 and 60 min, and this can be suppressed in Syk knockout cells, providing an effect similar that that seen under piceatannol treatment. The overexpression of Syk reverses this effect and leads to a significantly higher IRAK1 mRNA level. Collectively, our results strongly suggest that Syk plays a critical role in regulating both the activity and transcriptional level of IRAK1.

Folate Receptor-Targeted Diagnostics and Therapeutics for Inflammatory Diseases

Inflammation, an innate immune response mediated by macrophages, forms the first line of defence to protect our body from the invasion of various pathogens. Although inflammation is a defensive response, chronic inflammation has been regarded as the major cause of many types of human diseases such as inflammatory/autoimmune diseases, cancers, neurological diseases, and cardiovascular diseases. Folate receptor (FR) is a cell surface glycosylphosphatidylinositol (GPI)-anchored glycoprotein, and its three isoforms, FR-α, FR-β, and FR-γ, are found in humans. Interestingly, FRs are highly expressed on a variety of cells, including cancer cells and activated macrophages, whereas their expression on normal cells is undetectable, indicating that FR-targeting could be a good selective strategy for the diagnosis and therapeutic treatment of cancers and activated macrophage-mediated inflammatory diseases. Previous studies successfully showed FR-targeted imaging of many types of cancers in animal models as well as human patients. Recently, a number of emerging studies have found that activated macrophages, which are critical players for a variety of inflammatory diseases, highly express FRs, and selective targeting of these FR-positive activated macrophages is a good approach to diagnose and treat inflammatory diseases. In this review, we describe the characteristics and structure of FRs, and further discuss FR-targeted diagnostics and therapeutics of human diseases, in particular, activated macrophage-mediated inflammatory diseases.

Ionizing Radiation Induces Innate Immune Responses in Macrophages by Generation of Mitochondrial Reactive Oxygen Species

During radiotherapy for tumors, the innate immune system also responds to ionizing radiation and induces immune modulation. However, little is known about the molecular mechanisms by which radiation modulates innate immune responses. In this study, we observed that radiation triggered the generation of mitochondrial reactive oxygen species (mROS), leading to innate immune responses in murine bone marrow-derived macrophages (BMDM). Radiation-induced mROS was essential for robust induction of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-12p40 mRNA and protein in BMDM. Exposure to radiation also led to rapid activation of the mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB pathways in BMDM. Notably, radiation-induced MAPK activation and NF-κB signaling were regulated by mROS in macrophages. Additionally, radiation-induced expression of TNF-α, IL-6 and IL-12p40 was dependent on JNK, p38 and NF-κB activation in BMDM. These data suggest a key role for radiation-induced pro-inflammatory responses and activation of the MAPK and NF-κB pathways through a triggering mechanism involving mROS generation.

Regulation of Chemokine Activity - A Focus on the Role of Dipeptidyl Peptidase IV/CD26

Chemokines are small, chemotactic proteins that play a crucial role in leukocyte migration and are, therefore, essential for proper functioning of the immune system. Chemokines exert their chemotactic effect by activation of chemokine receptors, which are G protein-coupled receptors (GPCRs), and interaction with glycosaminoglycans (GAGs). Furthermore, the exact chemokine function is modulated at the level of posttranslational modifications. Among the different types of posttranslational modifications that were found to occur in vitro and in vivo, i.e., proteolysis, citrullination, glycosylation, and nitration, NH₂-terminal proteolysis of chemokines has been described most intensively. Since the NH₂-terminal chemokine domain mediates receptor interaction, NH₂-terminal modification by limited proteolysis or amino acid side chain modification can drastically affect their biological activity. An enzyme that has been shown to provoke NH₂-terminal proteolysis of various chemokines is dipeptidyl peptidase IV or CD26. This multifunctional protein is a serine protease that preferably cleaves dipeptides from the NH₂-terminal region of peptides and proteins with a proline or alanine residue in the penultimate position. Various chemokines possess such a proline or alanine residue, and CD26-truncated forms of these chemokines have been identified in cell culture supernatant as well as in body fluids. The effects of CD26-mediated proteolysis in the context of chemokines turned out to be highly complex. Depending on the chemokine ligand, loss of these two NH₂-terminal amino acids can result in either an increased or a decreased biological activity, enhanced receptor specificity, inactivation of the chemokine ligand, or generation of receptor antagonists. Since chemokines direct leukocyte migration in homeostatic as well as pathophysiologic conditions, CD26-mediated proteolytic processing of these chemotactic proteins may have significant consequences for appropriate functioning of the immune system. After introducing the chemokine family together with the GPCRs and GAGs, as main interaction partners of chemokines, and discussing the different forms of posttranslational modifications, this review will focus on the intriguing relationship of chemokines with the serine protease CD26.

Molecular association of CD98, CD29, and CD147 critically mediates monocytic U937 cell adhesion

Adhesion events of monocytes represent an important step in inflammatory responses induced by chemokines. The β1-integrin CD29 is a major adhesion molecule regulating leukocyte migration and extravasation. Although several adhesion molecules have been known as regulators of CD29, the molecular interactions between CD29 and its regulatory adhesion molecules (such as CD98 and CD147) have not been fully elucidated. Therefore, in this study, we examined whether these molecules are functionally, biochemically, and cell-biologically associated using monocytic U937 cells treated with aggregation-stimulating and blocking antibodies, as well as enzyme inhibitors. The surface levels of CD29, CD98, and CD147 (but not CD43, CD44, and CD82) were increased. The activation of CD29, CD98, and CD147 by ligation of them with aggregation-activating antibodies triggered the induction of cell-cell adhesion, and sensitivity to various enzyme inhibitors and aggregation-blocking antibodies was similar for CD29-, CD98-, and CD147-induced U937 cell aggregation. Molecular association between these molecules and the actin cytoskeleton was confirmed by confocal microscopy and immunoprecipitation. These results strongly suggest that CD29 might be modulated by its biochemical and cellular regulators, including CD98 and CD147, via the actin cytoskeleton.

Macrophage polarization in response to epigenetic modifiers during infection and inflammation

Macrophages are a heterogeneous population of phagocytic cells present in all tissues. Recently, several drugs that target the epigenetic machinery have emerged as attractive molecules for treating infection and inflammation by modulating macrophages. Treatment of lipopolysaccharide (LPS)-challenged macrophages with epigenetic modifiers leads to phenotype switching. This could provide stimulatory/destructive (M1) or suppressive/protective (M2) therapeutic strategies, which are crucial in the cytokine milieu in which the macrophages reside. In this review, we provide an overview of macrophage functional diversity during various diseases, including infection, as well as the current status in the development and clinical utility of epigenetic modifiers.

Chronic Iron Overload Results in Impaired Bacterial Killing of THP-1 Derived Macrophage through the Inhibition of Lysosomal Acidification

Iron is essential for living organisms and the disturbance of iron homeostasis is associated with altered immune function. Additionally, bacterial infections can cause major complications in instances of chronic iron overload, such as patients with transfusion-dependent thalassemia. Monocytes and macrophages play important roles in maintaining systemic iron homoeostasis and in defense against invading pathogens. However, the effect of iron overload on the function of monocytes and macrophages is unclear. We elucidated the effects of chronic iron overload on human monocytic cell line (THP-1) and THP-1 derived macrophages (TDM) by continuously exposing them to high levels of iron (100 μM) to create I-THP-1 and I-TDM, respectively. Our results show that iron overload did not affect morphology or granularity of I-THP-1, but increased the granularity of I-TDM. Bactericidal assays for non-pathogenic E. coli DH5α, JM109 and pathogenic P. aeruginosa all revealed decreased efficiency with increasing iron concentration in I-TDM. The impaired P. aeruginosa killing ability of human primary monocyte derived macrophages (hMDM) was also found when cells are cultured in iron contained medium. Further studies on the bactericidal activity of I-TDM revealed lysosomal dysfunction associated with the inhibition of lysosomal acidification resulting in increasing lysosomal pH, the impairment of post-translational processing of cathepsins (especially cathepsin D), and decreased autophagic flux. These findings may explain the impaired innate immunity of thalassemic patients with chronic iron overload, suggesting the manipulation of lysosomal function as a novel therapeutic approach.

Fulvic acid promotes extracellular anti-cancer mediators from RAW 264.7 cells, causing to cancer cell death in vitro

Fulvic acid (FA) is known to promote electrochemical balance as a donor or a receptor possessing many biomedical functions. Nevertheless, the effect of FA on the anti-cancer activity has not been elucidated. In the current study, we first isolated FA from humus and investigated whether FA regulates immune-stimulating functions, such as production of nitric oxide (NO), in RAW 264.7 cells. Our data showed that FA slightly enhances cell viability in a dose-dependent manner and secretion of NO from RAW 264.7 cells. It upregulated the protein and mRNA expression of inducible NO synthesis (iNOS). In addition, FA enhanced the DNA-binding activity of nuclear factor-κB (NF-κB) in RAW 264.7 cells; the NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC) effectively attenuated the expression of FA-stimulated iNOS, suggesting that FA stimulates NF-κB to promote iNOS and NO production. Finally, FA-stimulated culture media (FA-CM) from RAW 264.7 cells were collected and MCA-102 fibrosarcoma cells were cultured in this media. The FA-CM augmented MCA-102 fibrosarcoma cell apoptosis; however, an NO inhibitor N(G)-monomethyl-l-arginine (NMMA) slightly inhibited the FA-CM-mediated MCA-102 fibrosarcoma cell apoptosis, which was accompanied by low levels of NO. In the present study, we found that FA induces the generation of NO and iNOS in RAW 264.7 cells by inducing NF-κB activation; however, NO did not significantly stimulate MCA-102 fibrosarcoma cell apoptosis in the current study. In addition, FA-CM enhanced cell death in various human cancer cells such as Hep3B, LNCaP, and HL60. Taken together, FA most likely stimulates immune-modulating molecules such as NO and induces cancer cell apoptosis.

Double Roles of Macrophages in Human Neuroimmune Diseases and Their Animal Models

Macrophages are important immune cells of the innate immune system that are involved in organ-specific homeostasis and contribute to both pathology and resolution of diseases including infections, cancer, obesity, atherosclerosis, and autoimmune disorders. Multiple lines of evidence point to macrophages as a remarkably heterogeneous cell type. Different phenotypes of macrophages exert either proinflammatory or anti-inflammatory roles depending on the cytokines and other mediators that they are exposed to in the local microenvironment. Proinflammatory macrophages secrete detrimental molecules to induce disease development, while anti-inflammatory macrophages produce beneficial mediators to promote disease recovery. The conversion of the phenotypes of macrophages can regulate the initiation, development, and recovery of autoimmune diseases. Human neuroimmune diseases majorly include multiple sclerosis (MS), neuromyelitis optica (NMO), myasthenia gravis (MG), and Guillain-Barré syndrome (GBS) and macrophages contribute to the pathogenesis of these neuroimmune diseases. In this review, we summarize the double roles of macrophage in neuroimmune diseases and their animal models to further explore the mechanisms of macrophages involved in the pathogenesis of these disorders, which may provide a potential therapeutic approach for these disorders in the future.

DHA Suppresses Primary Macrophage Inflammatory Responses via Notch 1/ Jagged 1 Signaling

Persistent macrophages were observed in the lungs of murine offspring exposed to maternal LPS and neonatal hyperoxia. Maternal docosahexaenoic acid (DHA) supplementation prevented the accumulation of macrophages and improved lung development. We hypothesized that these macrophages are responsible for pathologies observed in this model and the effects of DHA supplementation. Primary macrophages were isolated from adult mice fed standard chow, control diets, or DHA supplemented diets. Macrophages were exposed to hyperoxia (O₂) for 24 h and LPS for 6 h or 24 h. Our data demonstrate significant attenuation of Notch 1 and Jagged 1 protein levels in response to DHA supplementation in vivo but similar results were not evident in macrophages isolated from mice fed standard chow and supplemented with DHA in vitro. Co-culture of activated macrophages with MLE12 epithelial cells resulted in the release of high mobility group box 1 and leukotriene B₄ from the epithelial cells and this release was attenuated by DHA supplementation. Collectively, our data indicate that long term supplementation with DHA as observed in vivo, resulted in deceased Notch 1/Jagged 1 protein expression however, DHA supplementation in vitro was sufficient to suppress release LTB₄ and to protect epithelial cells in co-culture.