TLR2 stimulation impairs anti-inflammatory activity of M2-like macrophages, generating a chimeric M1/M2 phenotype

Maintenance of homeostasis by TLR4 ligands

Immunotherapy is renowned for its capacity to elicit anti-infective and anti-cancer effects by harnessing immune responses to microbial components and bolstering innate healing mechanisms through a cascade of immunological reactions. Specifically, mammalian Toll-like receptors (TLRs) have been identified as key receptors responsible for detecting microbial components. The discovery of these mammalian Toll-like receptors has clarified antigen recognition by the innate immune system. It has furnished a molecular foundation for comprehending the interplay between innate immunity and its anti-tumor or anti-infective capabilities. Moreover, accumulating evidence highlights the crucial role of TLRs in maintaining tissue homeostasis. It has also become evident that TLR-expressing macrophages play a central role in immunity by participating in the clearance of foreign substances, tissue repair, and the establishment of new tissue. This macrophage network, centered on macrophages, significantly contributes to innate healing. This review will primarily delve into innate immunity, specifically focusing on substances targeting TLR4.

Immunomodulatory effects of curcumin on macrophage polarization in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by synovial inflammation, cartilage destruction, pannus formation and bone erosion. Various immune cells, including macrophages, are involved in RA pathogenesis. The heterogeneity and plasticity of macrophages render them pivotal regulators of both the induction and resolution of the inflammatory response. Predominantly, two different phenotypes of macrophages have been identified: classically activated M1 macrophages exacerbate inflammation via the production of cytokines, chemokines and other inflammatory mediators, while alternatively activated M2 macrophages inhibit inflammation and facilitate tissue repair. An imbalance in the M1/M2 macrophage ratio is critical during the initiation and progression of RA. Macrophage polarization is modulated by various transcription factors, epigenetic elements and metabolic reprogramming. Curcumin, an active component of turmeric, exhibits potent immunomodulatory effects and is administered in the treatment of multiple autoimmune diseases, including RA. The regulation of macrophage polarization and subsequent cytokine production as well as macrophage migration is involved in the mechanisms underlying the therapeutic effect of curcumin on RA. In this review, we summarize the underlying mechanisms by which curcumin modulates macrophage function and polarization in the context of RA to provide evidence for the clinical application of curcumin in RA treatment.

Circulating and Synovial Monocytes in Arthritis and Ex-Vivo Model to Evaluate Therapeutic Modulation of Synovial Monocytes

Monocytes are innate immune cells that play a dual role in protection of host against pathogens and initiation and perpetuation of inflammatory disorders including joint diseases. During inflammation, monocytes migrate from peripheral blood to tissues via chemokine receptors where they produce inflammatory factors. Monocytes are classified into three subsets, namely: classical, intermediate and non-classical, each subset has particular function. Synovium of patients with inflammatory joint diseases, such as rheumatoid arthritis and psoriatic arthritis as well as osteoarthritis, is enriched by monocytes that differ from circulatory ones by distinct subsets distribution. Several therapeutic agents used systemically or locally through intra-articular injections in arthritis management modulate monocyte subsets. This scoping review summarized the existing literature delineating the effect of common therapeutic agents used in arthritis management on circulating and synovial monocytes/macrophages. As certain agents have an inhibitory effect on monocytes, we propose to test their potential to inhibit synovial monocytes via an ex-vivo platform based on cultured synovial fluid mononuclear cells derived from patients with rheumatic diseases. Information obtained from the ex-vivo platform can be applied to explore the therapeutic potential of medications in clinical practice.

Macrophage polarization involved the inflammation of chronic obstructive pulmonary disease by S1P/HDAC1 signaling

Globally, chronic obstructive pulmonary disease (COPD) is the cause of high morbidity and mortality, and constitutes a huge public health burden. Previous studies have reported that inflammation is closely related to COPD, but its potential mechanism is still unclear. Since the polarization of macrophages is involved in regulating inflammation, we assume that COPD changes the polarization of macrophages. To verify this, we investigated the relationship between the expression of S1PR1, HADC1, and inflammatory macrophages in COPD patients via flow cytometry, qRT-PCR, and western blot analysis. We found that macrophages of COPD individuals differentiated into M1 phenotype, and the expression of S1PR1 increased and HDAC1 decreased. S1PR1 also inhibits the expression of HDAC1, so S1PR1/HDAC1 signal regulates the polarization of macrophages. The results of the study put forward new ideas of the pathogenesis of COPD, and also proposed the possible treatment options.

The Role of Toll-like Receptor-4 in Macrophage Imbalance in Lethal COVID-19 Lung Disease, and Its Correlation with Galectin-3

To the current data, there have been 6,955,141 COVID-19-related deaths worldwide, reported to WHO. Toll-like receptors (TLRs) implicated in bacterial and virus sensing could be a crosstalk between activation of persistent innate-immune inflammation, and macrophage's sub-population alterations, implicated in cytokine storm, macrophage over-activation syndrome, unresolved Acute Respiratory Disease Syndrome (ARDS), and death. The aim of this study is to demonstrate the association between Toll-like-receptor-4 (TLR-4)-induced inflammation and macrophage imbalance in the lung inflammatory infiltrate of lethal COVID-19 disease. Twenty-five cases of autopsy lung tissues were studied by digital pathology-based immunohistochemistry to evaluate expression levels of TLR-4 (CD 284), pan-macrophage marker CD68 (clone KP1), sub-population marker related to alveolar macrophage Galectin-3 (GAL-3) (clone 9C4), and myeloid derived CD163 (clone MRQ-26), respectively. SARS-CoV-2 viral persistence has been evaluated by in situ hybridation (ISH) method. This study showed TLR-4 up-regulation in a subgroup of patients, increased macrophage infiltration in both Spike-1(+) and Spike-1(-) lungs (p < 0.0001), and a macrophage shift with important down-regulation of GAL-3(+) alveolar macrophages associated with Spike-1 persistence (p < 0.05), in favor of CD163(+) myeloid derived monocyte-macrophages. Data show that TLR-4 expression induces a persistent activation of the inflammation, with inefficient resolution, and pathological macrophage shift, thus explaining one of the mechanisms of lethal COVID-19.

An Update on Toll-like Receptor 2, Its Function and Dimerization in Pro- and Anti-Inflammatory Processes

While a certain level of inflammation is critical for humans to survive infection and injury, a prolonged inflammatory response can have fatal consequences. Pattern recognition Toll-like receptors (TLRs) are key players in the initiation of an inflammatory process. TLR2 is one of the most studied pattern recognition receptors (PRRs) and is known to form heterodimers with either TLR1, TLR4, TLR6, and TLR10, allowing it to recognize a wide range of pathogens. Although a large number of studies have been conducted over the past decades, there are still many unanswered questions regarding TLR2 mechanisms in health and disease. In this review, we provide an up-to-date overview of TLR2, including its homo- and heterodimers. Furthermore, we will discuss the pro- and anti-inflammatory properties of TLR2 and recent findings in prominent TLR2-associated infectious and neurodegenerative diseases.

Laggera alata Attenuates Inflammatory Response by Regulating Macrophage Polarization in Rheumatoid Arthritis Mice

Rheumatoid arthritis (RA) is a type of joint injury, which can induce the activation of inflammatory factors and polarization of tissue macrophages. Total phenolics from Laggera alata (TPLA) has been reported to exhibit anti-inflammatory effect in various diseases. However, its specific function in RA is still unknown. Here, the protective properties of TPLA were studied in collagen-induced arthritis (CIA)-induced RA mice. RA mouse model was established through the CIA induction. Arthritis score, hind paw thickness, and the body weight of the RA mice were evaluated in each group. H&E staining was conducted in hind paw and joint tissues for histopathological staining. The distal femur was analyzed by microCT, and bone loss-related indicators were assessed. The expression of macrophage polarization markers was detected by immunofluorescence staining in RA mice. The serum levels of inflammatory markers were determined by enzyme-linked immunosorbent assay (ELISA). TPLA reduced the CIA-induced arthritis score and hind paw thickness in mice. The body weight of the CIA mouse was significantly increased by TPLA treatment. TPLA improved the CIA-induced histopathological changes in the hind paw and joint tissues from the mice. TPLA inhibited the bone loss and alleviated bone destruction in CIA mouse model. TPLA altered the macrophage phenotype from M1 macrophages into M2 in CIA mice. TPLA suppressed the levels of inflammatory markers both in the serum and joint tissues of the CIA mice. TPLA mitigated RA development by suppressing inflammatory reaction through the inhibition of M1 microphage polarization.

Damage-mediated macrophage polarization in sterile inflammation

Most of the leading causes of death, such as cardiovascular diseases, cancer, dementia, neurodegenerative diseases, and many more, are associated with sterile inflammation, either as a cause or a consequence of these conditions. The ability to control the progression of inflammation toward tissue resolution before it becomes chronic holds significant clinical potential. During sterile inflammation, the initiation of inflammation occurs through damage-associated molecular patterns (DAMPs) in the absence of pathogen-associated molecules. Macrophages, which are primarily localized in the tissue, play a pivotal role in sensing DAMPs. Furthermore, macrophages can also detect and respond to resolution-associated molecular patterns (RAMPs) and specific pro-resolving mediators (SPMs) during sterile inflammation. Macrophages, being highly adaptable cells, are particularly influenced by changes in the microenvironment. In response to the tissue environment, monocytes, pro-inflammatory macrophages, and pro-resolution macrophages can modulate their differentiation state. Ultimately, DAMP and RAMP-primed macrophages, depending on the predominant subpopulation, regulate the balance between inflammatory and resolving processes. While sterile injury and pathogen-induced reactions may have distinct effects on macrophages, most studies have focused on macrophage responses induced by pathogens. In this review, which emphasizes available human data, we illustrate how macrophages sense these mediators by examining the expression of receptors for DAMPs, RAMPs, and SPMs. We also delve into the signaling pathways induced by DAMPs, RAMPs, and SPMs, which primarily contribute to the regulation of macrophage differentiation from a pro-inflammatory to a pro-resolution phenotype. Understanding the regulatory mechanisms behind the transition between macrophage subtypes can offer insights into manipulating the transition from inflammation to resolution in sterile inflammatory diseases.

mRNA expression of immune factors by milk somatic cells from healthy Holstein lactating cows

This study investigated the mRNA of immune factors expressed by milk somatic cells from 72 healthy lactating Holstein cows on 1 farm. Milk samples were collected aseptically from the right front mammary gland before milking. The milk samples that had a negative reaction to the California mastitis test were used to analyze the mRNA of immune factors. Cows were divided into 2 groups based on the detection of bacteria in milk samples: positive group (n = 22 cows), which showed bacteria in cultures, and negative group (n = 50 cows), which did not show bacteria in cultures. There were significant positive correlations among the relative mRNA levels of interleukin (IL)-6, IL-8, arginase 1, chemokine (C-C motif) ligand (CCL) 1, and chemokine (C-X-C motif) ligand (CXCL) 13, as well as among the relative mRNA levels of IL-10, pentraxin 3, CCL5, and CCL14. Significantly high levels of IL-1β, IL-6, IL-8, arginase 1, Batf, CCL1, CXCL14, and toll-like receptor 4 in the positive group were discovered compared to the negative group. These results suggest that the presence of bacteria in lactating healthy dairy cows may affect mRNA levels of inflammatory mediators expressed by somatic cells.

P-Hydroxylcinnamaldehyde induces tumor-associated macrophage polarization toward the M1 type by regulating the proteome and inhibits ESCC in vivo and in vitro

P-Hydroxylcinnamaldehyde (CMSP) was firstly isolated from Chinese medicine Cochinchinnamomordica seed (CMS) by our team and has been verified to have growth-inhibiting abilities in malignant tumors including esophageal squamous cell carcinoma (ESCC). However, the detailed mechanism of its function is still unclear. Tumor-associated macrophages (TAMs) are an essential component of the tumor microenvironment (TME), playing important roles in tumor growth, metastasis, angiogenesis, and epithelial-mesenchymal transition (EMT). In the present study, we found that the percentage of M1-like macrophages was significantly increased in TME of ESCC cell derivedxenograft tumor model after CMSP treatment, while the ratios of other immune cells showed relatively low variation. To confirm these results, we further examined the effect of CMSP on macrophage polarization in vitro. The results revealed that CMSP also could induce phorbol-12-myristate-13-acetate (PMA)-induced M0 macrophages from THP-1 and mouse peritoneal macrophages toward the M1-like macrophages. Furthermore, CMSP could exert anti-tumor effect through TAMs in vitro co-culture model, in addition, the growth inhibition effect of CMSP was partly abolished in macrophage depletion model. To determine the potential pathway of CMSP induced polarization, we used quantitative proteomics (label-free) technology to explore the proteomic changes under CMSP treatment. The results revealed that immune-activating protein and M1 macrophage biomarkers were significantly increased after CMSP treatment. More importantly, CMSP stimulated pathways related to M1 macrophage polarization, such as the NF-κB signaling pathway and Toll-like receptor pathway, indicating that CMSP might induce M1-type macrophage polarization through these pathways. In conclusion, CMSP can regulate immune microenvironment in vivo and induce TAM polarization toward the M1 type by promoting proteomic changes, and exert anti-tumor effect through TAMs.

Innate immune activation and modulatory factors of Helicobacter pylori towards phagocytic and nonphagocytic cells

Helicobacter pylori is an intriguing obligate host-associated human pathogen with a specific host interaction biology, which has been shaped by thousands of years of host-pathogen coevolution. Molecular mechanisms of interaction of H. pylori with the local immune cells in the human system are less well defined than epithelial cell interactions, although various myeloid cells, including neutrophils and other phagocytes, are locally present or attracted to the sites of infection and interact with H. pylori. We have recently addressed the question of novel bacterial innate immune stimuli, including bacterial cell envelope metabolites, that can activate and modulate cell responses via the H. pylori Cag type IV secretion system. This review article gives an overview of what is currently known about the interaction modes and mechanisms of H. pylori with diverse human cell types, with a focus on bacterial metabolites and cells of the myeloid lineage including phagocytic and antigen-presenting cells.

Macrophages in aseptic loosening: Characteristics, functions, and mechanisms

Aseptic loosening (AL) is the most common complication of total joint arthroplasty (TJA). Both local inflammatory response and subsequent osteolysis around the prosthesis are the fundamental causes of disease pathology. As the earliest change of cell behavior, polarizations of macrophages play an essential role in the pathogenesis of AL, including regulating inflammatory responses and related pathological bone remodeling. The direction of macrophage polarization is closely dependent on the microenvironment of the periprosthetic tissue. When the classically activated macrophages (M1) are characterized by the augmented ability to produce proinflammatory cytokines, the primary functions of alternatively activated macrophages (M2) are related to inflammatory relief and tissue repair. Yet, both M1 macrophages and M2 macrophages are involved in the occurrence and development of AL, and a comprehensive understanding of polarized behaviors and inducing factors would help in identifying specific therapies. In recent years, studies have witnessed novel discoveries regarding the role of macrophages in AL pathology, the shifts between polarized phenotype during disease progression, as well as local mediators and signaling pathways responsible for regulations in macrophages and subsequent osteoclasts (OCs). In this review, we summarize recent progress on macrophage polarization and related mechanisms during the development of AL and discuss new findings and concepts in the context of existing work.

Akkermansia muciniphila exerts immunomodulatory and anti-inflammatory effects on gliadin-stimulated THP-1 derived macrophages

Macrophages (MQs) pro-inflammatory phenotype is triggered by gliadin peptides. Akkermansia muciniphila (A. muciniphila) showed to enhance the anti-inflammatory phenotype of MQs. This study aimed to investigate the anti-inflammatory effects of A. muciniphila, on gliadin stimulated THP-1 derived macrophages. THP-1 cell line monocytes were differentiated into MQs by phorbol 12-myristate 13-acetate (PMA). MQs were treated with A. muciniphila before and after stimulation with gliadin (pre- and post-treat). CD11b, as a marker of macrophage differentiation, and CD206 and CD80, as M1 and M2 markers, were evaluated by flow cytometry technique. The mRNA expression of TGF-β, IL-6, and IL-10 and protein levels of IL-10 and TNF-α were measured by RT-PCR and ELISA techniques, respectively. Results show an increased percentage of M1 phenotype and release of proinflammatory cytokines (like TNF-α and IL-6) by macrophages upon incubation with gliadin. Pre- and post-treatment of gliadin-stimulated macrophages with A. muciniphila induced M2 phenotype associated with decreased proinflammatory (IL-6, TNF-α) and increased anti-inflammatory (IL-10, TGF-β) cytokines expression relative to the group that was treated with gliadin alone. This study suggests the potential beneficial effect of A. muciniphila on gliadin-stimulated MQs and the importance of future studies focusing on their exact mechanism of action on these cells.

The imbalance of liver resident macrophages polarization promotes chronic autoimmune hepatitis development in mice

Background

Autoimmune hepatitis (AIH) is a chronic immune-mediated inflammatory liver disease. At present, it is largely unknown how the innate immune cells influence AIH development.

Objective

To inquiry about mechanism of liver resident macrophages in AIH development, thus offering a new direction for AIH targeted treatment.

Methods

The liver resident macrophages were eliminated by clodronate liposomes in AIH liver tissues, followed by HE and Picrosirius assay to detect liver fibrosis and lymphocyte infiltration. The liver resident macrophages polarization was detected by Immunohistochemistry and qPCR. The collagenase digestion was used to isolate Kupffer cells from AIH mice liver tissues and pro-/anti-inflammatory cytokines were determined by qPCR.

Results

M2 macrophages were the dominant phenotype at early immune response stage and hepatic inflammation was progressively aggravated after depletion of liver resident macrophages. M2 macrophages could effectively delay the development of AIH and could be polarized to M1 macrophages at the disease progresses. TLR2 ligands could promote M2 macrophages producing anti-inflammatory cytokines, whereas TLR4 ligands could promote M1 macrophages producing proinflammatory cytokines. The change of TLR2 and TLR4 ligands could lead to continuous high expression of TLR4 and decreased expression of TLR2 in macrophages to further affect liver resident macrophages polarization state.

Conclusion

TLR2 and TLR4 ligands mediated liver resident macrophages polarization to favor chronic autoimmune hepatitis development.

Synovial macrophages of rheumatoid arthritic mice protectively responded by altered M1/M2 differentiation after antibody blocking of TNFR1 and IL-1R

Rheumatoid arthritis (RA) primarily affecting the synovial tissue, has emerged as a major concern leading to the pressing need to develop effective treatment strategies. In the affected synovial tissue, resident macrophages play a pivotal role in the pathogenesis of RA. TNF-α and IL-1β released from pro-inflammatory M1 synovial macrophages are the master regulators of chronic joint inflammation. In this study collagen-induced rheumatoid arthritis model was developed in mice and post isolation, macrophages were subjected to administration with neutralizing antibodies IL1R and TNFR1 either alone or in combination. Flow cytometric analysis followed by Western blots, ROS, and IL-1β, TNF-α release assays were performed. Outcomes suggested that post-dual blockade of IL1R and TNFR1 arthritic synovial macrophages showed a shifting of the M1 towards the anti-inflammatory M2 phenotype. Moreover, the switch towards the M2 phenotype might be responsible for decreased levels of IL-1β,TNF-α, and ROS and simultaneous elevation in the activity of antioxidant enzymes like SOD, CAT, and GP_X content in the isolated macrophages. Simultaneous blocking of both IL1R and TNFR1 also showed a sharp reduction in the expression of NF-κB and SAPK-JNK. The elevated arginase and GR_X activity further confirmed the polarization towards M2. Moreover, bioinformatics analysis was performed,and it was found that blocking TNFR1 with an antibody could hamper the binding of TNF to TNFR1 in the TNF-TNFR1 pathway. Thus, it may be inferred that dual blockade of IL1R and TNFR1 and a suitable antibody blocking of TNFR1 might be alternative therapeutic approaches for the regulation of RA-induced inflammation in the future.

Reprogramming the tumor microenvironment with biotechnology

The tumor microenvironment (TME) is a unique environment that is developed by the tumor and controlled by tumor-induced interactions with host cells during tumor progression. The TME includes immune cells, which can be classified into two types: tumor- antagonizing and tumor-promoting immune cells. Increasing the tumor treatment responses is associated with the tumor immune microenvironment. Targeting the TME has become a popular topic in research, which includes polarizing macrophage phenotype 2 into macrophage phenotype 1 using Toll-like receptor agonists with cytokines, anti-CD47, and anti-SIPRα. Moreover, inhibiting regulatory T cells through blockades and depletion restricts immunosuppressive cells in the TME. Reprogramming T cell infiltration and T cell exhaustion improves tumor infiltrating lymphocytes, such as CD8⁺ or CD4⁺ T cells. Targeting metabolic pathways, including glucose, lipid, and amino acid metabolisms, can suppress tumor growth by restricting the absorption of nutrients and adenosine triphosphate energy into tumor cells. In conclusion, these TME reprogramming strategies exhibit more effective responses using combination treatments, biomaterials, and nanoparticles. This review highlights how biomaterials and immunotherapy can reprogram TME and improve the immune activity.

Noncoding RNAs in Vascular Cell Biology and Restenosis

In-stent restenosis (ISR), characterised by ≥50% re-narrowing of the target vessel, is a common complication following stent implantation and remains a significant challenge to the long-term success of angioplasty procedures. Considering the global burden of cardiovascular diseases, improving angioplasty patient outcomes remains a key priority. Noncoding RNAs (ncRNAs) including microRNA (miRNA), long noncoding RNA (lncRNA) and circular RNA (circRNA) have been extensively implicated in vascular cell biology and ISR through multiple, both distinct and overlapping, mechanisms. Vascular smooth muscle cells, endothelial cells and macrophages constitute the main cell types involved in the multifactorial pathophysiology of ISR. The identification of critical regulators exemplified by ncRNAs in all these cell types and processes makes them an exciting therapeutic target in the field of restenosis. In this review, we will comprehensively explore the potential functions and underlying molecular mechanisms of ncRNAs in vascular cell biology in the context of restenosis, with an in-depth focus on vascular cell dysfunction during restenosis development and progression. We will also discuss the diagnostic biomarker and therapeutic target potential of ncRNAs in ISR. Finally, we will discuss the current shortcomings, challenges, and perspectives toward the clinical application of ncRNAs.

Bacteroides fragilis participates in the therapeutic effect of methotrexate on arthritis through metabolite regulation

Methotrexate (MTX) is a preferred disease-modifying anti-rheumatic drug in the management of rheumatoid arthritis (RA). However, the toxicity and inefficiency of MTX limit its clinical application. Gut microbiota has been implicated in the side effects and efficacy of MTX. In this study, the analysis of the gut microbiota in RA patients revealed that the abundances of intestinal Bacteroides fragilis was reduced after MTX treatment. We observed that MTX has no obvious therapeutic effect in the absence of B. fragilis, while transplantation of B. fragilis restored the efficacy of MTX in antibiotics-pretreated collagen-induced arthritis (CIA) mice. In addition, B. fragilis gavage was accompanied by an increase in butyrate. Supplementation of butyrate restored the response to MTX in gut microbiota-deficient mice, to a similar level achieved by B. fragilis gavage. These results show that gut microbiota-regulated butyrate plays an essential role in the efficacy of MTX, which will provide new strategies to improve the effectiveness of methotrexate in RA treatment.

Antiviral Innate Immune Responses in Autoimmunity: Receptors, Pathways, and Therapeutic Targeting

Innate immune receptors sense nucleic acids derived from viral pathogens or self-constituents and initiate an immune response, which involves, among other things, the secretion of cytokines including interferon (IFN) and the activation of IFN-stimulated genes (ISGs). This robust and well-coordinated immune response is mediated by the innate immune cells and is critical to preserving and restoring homeostasis. Like an antiviral response, during an autoimmune disease, aberrations of immune tolerance promote inflammatory responses to self-components, such as nucleic acids and immune complexes (ICs), leading to the secretion of cytokines, inflammation, and tissue damage. The aberrant immune response within the inflammatory milieu of the autoimmune diseases may lead to defective viral responses, predispose to autoimmunity, or precipitate a flare of an existing autoimmune disease. Herein, we review the literature on the crosstalk between innate antiviral immune responses and autoimmune responses and discuss the pitfalls and challenges regarding the therapeutic targeting of the mechanisms involved.

The role of macrophage subtypes and exosomes in immunomodulation

Macrophages are influential members of the innate immune system that can be reversibly polarized by different microenvironment signals. Cell polarization leads to a wide range of features, involving the migration, development, and organization of the cells. There is mounting evidence that macrophage polarization plays a key role in the initiation and development of a wide range of diseases. This study aims to give an overview of macrophage polarization, their different subtypes, and the importance of alternatively activated M2 macrophage and classically activated M1 macrophage in immune responses and pathological conditions. This review provides insight on the role of exosomes in M1/M2-like macrophage polarization and their potential as a promising therapeutic candidate.

Synovial Macrophages: Past Life, Current Situation, and Application in Inflammatory Arthritis

Inflammatory arthritis is an inflammatory disease that involves the joints and surrounding tissues. Synovial hyperplasia often presents when joints become inflamed due to immune cell infiltration. Synovial membrane is an important as well as a highly specific component of the joint, and its lesions can lead to degeneration of the joint surface, causing pain and joint disability or affecting the patients’ quality of life in severe cases. Synovial macrophages (SMs) are one of the cellular components of the synovial membrane, which not only retain the function of macrophages to engulf foreign bodies in the joint cavity, but also interact with synovial fibroblasts (SFs), T cells, B cells, and other inflammatory cells to promote the production of a variety of pro-inflammatory cytokines and chemokines, such as TNF-α, IL-1β, IL-8, and IL-6, which are involved in the pathogenic process of inflammatory arthritis. SMs from different tissue sources have differently differentiated potentials and functional expressions. This article provides a summary on studies pertaining to SMs in inflammatory arthritis, and explores their role in its treatment, in order to highlight novel treatment modalities for the disease.

Roles of Fatty Acids in Microglial Polarization: Evidence from In Vitro and In Vivo Studies on Neurodegenerative Diseases

Microglial polarization to the M1 phenotype (classically activated) or the M2 phenotype (alternatively activated) is critical in determining the fate of immune responses in neurodegenerative diseases (NDs). M1 macrophages contribute to neurotoxicity, neuronal and synaptic damage, and oxidative stress and are the first line of defense, and M2 macrophages elicit an anti-inflammatory response to regulate neuroinflammation, clear cell debris, and promote neuroregeneration. Various studies have focused on the ability of natural compounds to promote microglial polarization from the M1 phenotype to the M2 phenotype in several diseases, including NDs. However, studies on the roles of fatty acids in microglial polarization and their implications in NDs are a rare find. Most of the studies support the role of polyunsaturated fatty acids (PUFAs) in microglial polarization using cell and animal models. Thus, we aimed to collect data and provide a narrative account of microglial types, markers, and studies pertaining to fatty acids, particularly PUFAs, on microglial polarization and their neuroprotective effects. The involvement of only PUFAs in the chosen topic necessitates more in-depth research into the role of unexplored fatty acids in microglial polarization and their mechanistic implications. The review also highlights limitations and future challenges.

Transcription factor KLF4 regulated STAT1 to promote M1 polarization of macrophages in rheumatoid arthritis

This study aimed to reveal the mechanism of transcription factor Kruppel-like factor 4 (KLF4) in regulating M1 polarization of macrophages in rheumatoid arthritis (RA) in order to induce inflammatory response. The results suggested that KLF4 overexpression promoted the M1 polarization of RAW 264.7 cells, increased STAT1 expression and up-regulated the phosphorylation level. After KLF4 silencing, the M1 polarization level was down-regulated. Besides, the induced M1 macrophages were co-cultured with articular chondrocytes. KLF4 overexpression further aggravated chondrocyte injury, increased the cell apoptosis rate and activated the inflammatory injury. However, pretreatment with STAT1 inhibitor Cerulomycin resisted the effect of KLF4, and significantly suppressed STAT1 expression and M1 polarization of cells. KLF4 overexpression aggravated synovial tissue injury in mouse joints, up-regulated the expression of inflammatory factors, and increased the levels of CD86 and STAT1.

It was discovered that transcription factor KLF4 promoted the transcription of STAT1 to regulate the M1 polarization of macrophages, thus aggravating the progression of RA and inflammatory response.

Peptidoglycan-Like Components in Z-100, Extracted from Mycobacterium tuberculosis Strain Aoyama B, Increase IL-12p40 via NOD2

Background. Z-100 is a hot-water extract of the human-type Mycobacterium tuberculosis strain Aoyama B. While Z-100’s macrophage-mediated immunomodulatory effects have been reported, the mechanistic details have not been fully clarified. Here, we studied the immunomodulatory effects of Z-100 on mouse bone marrow-derived cells, human CD14+ cells, and skin. Methods. Mouse bone marrow-derived cells and CD14+ cells were cultured in the presence of granulocyte-macrophage colony-stimulating factor, differentiated into macrophage-like cells, and then stimulated with Z-100. Furthermore, since Z-100 is subcutaneously administered clinically, we injected Z-100 into mice and measured gene expression in the skin. Results. While Z-100 stimulation increased the production of interleukin- (IL-) 12p40 and IL-1β in mouse bone marrow-derived macrophages, levels of IL-1β were low. In contrast, TNF-α production did not increase. Meanwhile, stimulation of human CD14+ cells with Z-100 increased production of IL-12p40, TNF-α, and IL-1β. Because Z-100 appeared to have the most stable effect on IL-12p40, we examined the components of Z-100 that induce IL-12p40 production. We found that Z-100 contained peptidoglycan-like components. In addition, an siRNA study showed that Z-100 increased the production of IL-12p40 via nucleotide-binding oligomerization domain 2 (NOD2). Further, subcutaneous administration of Z-100 to mice significantly elevated expression of IL-12p40 and IL-1β and showed a trend towards increasing TNF-α in the skin. Conclusion. Z-100 induced the production of immunomodulatory cytokines from various types of macrophages and specifically increased IL-12p40 production through peptidoglycan-like components via NOD2.

Proteomic networks associated with tumor-educated macrophage polarization and cytotoxicity potentiated by heat-killed tuberculosis

Local administration of attenuated mycobacterium has been used as a cancer treatment adjuvant to re-boost patient immune responses with variable clinical outcomes. We aimed to clarify the impact of attenuated heat-killed tuberculosis (HKTB) on tumor-associated macrophages which play critical roles in shaping immunological regulation in the tumor microenvironment. Upon HKTB stimulation, both primary macrophages derived from the peripheral blood of healthy subjects and from lung cancer patients as well as THP1-derived classically activated macrophages (Ms) and tumor-educated macrophages (TEMs) were polarized into the proinflammatory phenotype, as characterized by increased expression cluster of differentiation 86. A quantitative proteomic analysis revealed that stimulated TEMs were unable to activate the toll-like receptor 2, signal transducer and activator of transcription 1, or nuclear factor-κB signaling. Instead, they showed distinct intercellular adhesion molecule 1 signaling, impaired cell adhesion, and mitochondrial dysfunction. These molecular mechanisms might contribute to lower cytotoxicity of HKTB-stimulated TEMs against A549 cells via the release of distinct inflammatory cytokines compared to HKTB-stimulated Ms. Our study provides an unbiased and systematic interpretation of cellular and molecular alterations of HKTB-reeducated macrophages which should help illuminate potential strategies of HKTB-stimulated macrophage-based combination therapy for cancer treatment.

The role of Sirt6 in osteoarthritis and its effect on macrophage polarization

Osteoarthritis (OA), the commonest arthritis type, features irreversible cartilage loss and synovitis. It was reported that macrophages have an important function in synovial inflammation, and our team revealed that the amounts of Sirt6, a nicotinamide adenine dinucleotide (NAD)⁺-dependent histone deacetylase, decrease during synovial inflammation and osteoarthritis. This work aimed to examine the anti-inflammatory properties of Sirt6 in synovial inflammation. Firstly, we compared Sirt6 amounts in acute meniscus injury and OA human knee synovial tissue samples by immunofluorescence and immunoblot. Secondly, Sirt6ʹs suppressive effects on inflammatory markers and macrophage polarization were evaluated. Finally, OA mice were histologically evaluated, and serum inflammatory factors were detected for assessing the impact of Sirt6 overexpression on the mouse synovium. We found significantly lower interleukin-4 (IL-4) amounts and M2 polarization in OA patients compared with control individuals. The expression of Sirt6 was lower in RAW264.7 cells of the lipopolysaccharides (LPS) + interferon-gamma (IFN-γ) group compared with the phosphate buffer saline (PBS) group, but higher than in the IL-4 group. The polarization of macrophages affected Sirt6 expression, which was reduced and elevated in M1 and M2 macrophages, respectively. Sirt6 inhibition could promote the release of proinflammatory cytokines by macrophages in the synovial membrane, induce M1 polarization in macrophages and inhibit M2 polarization in vitro, and Sirt6 overexpression alleviated osteoarthritis in vivo. These data strongly suggested that Sirt6 could inhibit synovial inflammation. Thus, this study provides a novel therapeutic target in osteoarthritis.

The Unitary Micro-Immunotherapy Medicine Interferon-γ (4 CH) Displays Similar Immunostimulatory and Immunomodulatory Effects than Those of Biologically Active Human Interferon-γ on Various Cell Types

As a cytokine, gamma-interferon (IFN-γ) is considered a key player in the fine-tuned orchestration of immune responses. The extreme cellular sensitivity to cytokines is attested by the fact that very few of these bioactive molecules per cell are enough to trigger cellular functions. These findings can, at least partially, explain how/why homeopathically-prepared cytokines, and especially micro-immunotherapy (MI) medicines, are able to drive cellular responses. We focused our fundamental research on a unitary MI preparation of IFN-γ, specifically employed at 4 CH, manufactured and impregnated onto sucrose-lactose pillules as all other MI medicines. We assessed the IFN-γ concentration in the medium after dilution of the IFN-γ (4 CH)-bearing pillules and we evaluated in vitro drug responses in a wide range of immune cells, and in endothelial cells. Our results showed that IFN-γ (4 CH) stimulated the proliferation, the activation and the phagocytic capabilities of primary immune cells, as well as modulated their cytokine-secretion and immunity-related markers’ expression in a trend that is quite comparable with the well-recognized biological effects induced by IFN-γ. Altogether, these data provide novel and additional evidences on MI medicines, and specifically when active substances are prepared at 4 CH, thus suggesting the need for more investigations.

SAA induces suppressive neutrophils via the TLR2-mediated signaling pathway to promote progression of breast cancer

Immune inflammation plays a key role in breast cancer development, progression, and therapeutic efficacy. Neutrophils are crucial for the regulation of the suppressive tumor microenvironment and are associated with poor clinical survival. However, the mechanisms underlying the activation of suppressive neutrophils in breast cancer are poorly understood. Here, we report that breast cancer cells secrete abundant serum amyloid A 1 (SAA1), which is associated with the accumulation of suppressive neutrophils. High expression of SAA1 in breast cancer induces neutrophil immunosuppressive cytokine production through the activation of toll like receptor 2 (TLR2)-mediated signaling pathways. These include the TLR2/myeloid differentiation primary response 88 (MYD88)-mediated phosphatidylinositol 3-kinase (PI3K)/nuclear factor κB (NF-κB) signaling pathway and p38 mitogen-activated protein kinase (MAPK)-associated apoptosis resistance pathway, which eventually promote the progression of breast cancer. Our study demonstrates a mechanistic link between breast cancer cell secretion of SAA1 and suppressive neutrophils that potentiate tumor progression. These findings provide potential therapeutic targets for breast cancer.

Mechanism of protection from insulin resistance by toll-like receptor 2 deficiency in high-fat diet fed mice: involvement in macrophage polarization

BACKGROUND

Toll-like receptor 2 (TLR2) deficiency can increase insulin sensitivity and improves glucose tolerance. However, it is not yet fully understood about its underlying mechanism. The regulation of M1/M2 macrophage polarization has been verified to involve in insulin resistance. Here, we evaluated whether the beneficial effect of TLR2 deficiency is mediated by TLR2-associated macrophage polarization in mice fed with high-fat diet (HFD).

METHODS AND RESULTS

Wild-type and TLR2 knockout (TLR2^-/-) mice received HFD for two months. Following intraperitoneal glucose tolerance and insulin resistance tests, peripheral monocytes were isolated, and in vitro induced for differentiation into M1 and M2 macrophages, respectively. Macrophages polarization was evaluated using flow cytometry. The expression of macrophage polarization marker genes and cytokine production in visceral adipose tissue were measured by qRT-PCR and ELISA. Compared to wild-type mice, TLR2^-/- mice showed higher glucose tolerance and insulin sensitivity, along with significantly reduced the population of M1 and increased M2 count in vitro. Additionally, TLR2^-/- mice demonstrated higher expression of M2 marker iNOS mRNA and interleukin-10 level in adipose tissues.

CONCLUSIONS

Our results reveal that TLR2 knockout-mediated macrophages M2 polarization is a crucial factor for preventing against diet-induced insulin resistance in mice. These findings deepen our knowledge about the mechanism underlying HFD-induced insulin resistance.

CTLA4-Ig treatment induces M1-M2 shift in cultured monocyte-derived macrophages from healthy subjects and rheumatoid arthritis patients

Background

In rheumatoid arthritis (RA), macrophages play an important role in modulating the immunoinflammatory response through their polarisation into “classically” (M1) or “alternatively activated” (M2) phenotypes. In RA, CTLA4-Ig (abatacept) reduces the inflammatory activity of macrophages by interacting with the costimulatory molecule CD86. The study aimed to investigate the efficacy of CTLA4-Ig treatment to induce an M2 phenotype both in M1-polarised monocyte-derived macrophages (MDMs) obtained from healthy subjects (HS) and in cultured MDMs obtained from active RA patients.

Methods

Cultured MDMs were obtained from peripheral blood mononuclear cells of 7 active RA patients and from 10 HS after stimulation with phorbol myristate acetate (5 ng/mL) for 24 h. HS-MDMs were then stimulated with lipopolysaccharide (LPS, 1 mg/mL) for 4 h to induce M1-MDMs. M1-MDMs and RA-MDMs were treated with CTLA4-Ig (100 μM and 500 μM) for 3, 12, 24, and 48 h. The gene expression of CD80, CD86, and TLR4 (M1 markers); CD163, CD204, and CD206 (surface M2 markers); and MerTK (functional M2 marker) was evaluated by qRT-PCR. The protein synthesis of surface M2 markers was investigated by Western blotting. The statistical analysis was performed by the Wilcoxon t-test.

Results

In LPS-induced HS-M1-MDMs, CTLA4-Ig 100 μM and 500 μM significantly downregulated the gene expression of M1 markers (3 h p<0.01 for all molecules; 12 h p<0.05 for TLR4 and CD86) and significantly upregulated that of M2 markers, primarily after 12 h of treatment (CD163: p < 0.01 and p < 0.05; CD206: p < 0.05 and p < 0.01; CD204: p < 0.05 by 100 mg/mL). Moreover, in these cells, CTLA4-Ig 500 μM increased the protein synthesis of surface M2 markers (p < 0.05). Similarly, in RA-MDMs, the CTLA4-Ig treatment significantly downregulated the gene expression of M1 markers at both concentrations primarily after 12 h (p < 0.05). Furthermore, both concentrations of CTLA4-Ig significantly upregulated the gene expression of CD206 (after 3 h of treatment; p < 0.05), CD163, and MerTK (after 12 h of treatment, p < 0.05), whereas CD204 gene expression was significantly upregulated by the high concentration of CTLA4-Ig (p < 0.05). The protein synthesis of all surface markers was increased primarily by CTLA4-Ig 500 μM, significantly for CD204 and CD206 after 24 h of treatment (p < 0.05).

Conclusions

CTLA4-Ig treatment seems to induce the in vitro shift from M1 to M2 macrophages, of both HS-M1-MDMs and RA-MDMs, as observed by the significant downregulation exerted on selected M1 markers and the upregulation of selected M2 markers suggesting an additional mechanism for its modulation of the RA inflammatory process.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02691-9.

Effect of Acinetobacter lwoffii on the modulation of macrophage activation and asthmatic inflammation

BACKGROUND

Although lung macrophages are directly exposed to external stimuli, their exact immunologic roles in asthma are still largely unknown. The aim of this study was to investigate the anti-asthmatic effect of Acinetobacter lwoffii in terms of lung macrophage modulation.

METHODS

Six-week-old female BALB/c mice were sensitized and challenged with ovalbumin (OVA) with or without intranasal administration of A. lwoffii during the sensitization period. Airway hyperresponsiveness and inflammation were evaluated. Using flow cytometry, macrophages were subclassified according to their activation status. In the in vitro study, a murine alveolar macrophage cell line (MH-S) treated with or without A. lwoffii before IL-13 stimulation were analysed by quantitative RT-PCR.

RESULTS

In a murine asthma model, the number of inflammatory cells, including macrophages and eosinophils, decreased in mice treated with A. lwoffii (A. lwoffii/OVA group) compared with untreated mice (OVA group). The enhanced expression of MHCII in macrophages in the OVA group was decreased by A. lwoffii treatment. M2 macrophage subtypes were significantly altered. A. lwoffii treatment decreased CD11b⁺ M2a and CD11b⁺ M2c macrophages, which showed strong positive correlations with Th2 cells, ILC2 and eosinophils. In contrast, CD11b⁺ M2b macrophages were significantly increased by A. lwoffii treatment and showed strong positive correlations with ILC1 and ILC3. In vitro, A. lwoffii down-regulated the expression of M2 markers related but up-regulated those related to M2b macrophages.

CONCLUSIONS AND CLINICAL RELEVANCE

Intranasal A. lwoffii exposure suppresses asthma development by suppressing the type 2 response via modulating lung macrophage activation, shifting M2a and M2c macrophages to M2b macrophages.

Polarized Macrophages in Periodontitis: Characteristics, Function, and Molecular Signaling

Periodontitis (PD) is a common chronic infectious disease. The local inflammatory response in the host may cause the destruction of supporting periodontal tissue. Macrophages play a variety of roles in PD, including regulatory and phagocytosis. Moreover, under the induction of different factors, macrophages polarize and form different functional phenotypes. Among them, M1-type macrophages with proinflammatory functions and M2-type macrophages with anti-inflammatory functions are the most representative, and both of them can regulate the tendency of the immune system to exert proinflammatory or anti-inflammatory functions. M1 and M2 macrophages are involved in the destructive and reparative stages of PD. Due to the complex microenvironment of PD, the dynamic development of PD, and various local mediators, increasing attention has been given to the study of macrophage polarization in PD. This review summarizes the role of macrophage polarization in the development of PD and its research progress.

Inhibition of Knee Osteoarthritis Progression in Mice by Administering SRT2014, an Activator of Silent Information Regulator 2 Ortholog 1

OBJECTIVE

Previous findings suggest that silent information regulator 2 ortholog 1 (SIRT1) plays essential roles in chondrocytes and prevents osteoarthritis (OA) development. The purpose of this study was to investigate the effects of intraperitoneal (i.p.) and intra-articular (i.a.) administration of the SIRT1 activator SRT2104, which has been approved for use in humans.

DESIGN

OA was induced by destabilizing the medial meniscus in the knee joint of 12-week-old CL57BL/6J mice. The mice were divided into 3 groups, that is, the control group, SRT2104 i.p.-injection group, and SRT2104 i.a.-injection group. Tissues were harvested at 4, 8, 12, and 16 weeks postsurgery. OA progression was evaluated using the Osteoarthritis Research Society International (OARSI) score. The production of OA-related proteins in cartilage and synovium was examined by immunohistochemistry.

RESULTS

OARSI scores in the control group were significantly higher at 8 and 12 weeks compared with other 2 groups. Immunohistochemical analysis showed that Sirt1 and type-2 collagen significantly increased, whereas MMP-13, ADAMTS-5, IL-1β, IL-6, cleaved caspase 3, PARP p85, acetylated NF-κB p65, and iNOS decreased significantly in cartilage tissues from the i.p. and i.a, SRT2104 groups. In the synovium, more iNOS-positive M1-like macrophages were observed in the control group than in the i.p. and i.a, SRT2104 groups, whereas more CD206-positive M2-like macrophages were detected in the i.p. and i.a. SRT2104 groups.

CONCLUSIONS

Both i.p. and i.a. SRT2104 injection reduced OA progression in the mouse OA model, suggesting that SRT2104 can serve as a new treatment for OA.

Curcumin Alleviated Dextran Sulfate Sodium-Induced Colitis by Regulating M1/M2 Macrophage Polarization and TLRs Signaling Pathway

Curcumin has shown good efficacy in mice with experimental colitis and in patients with ulcerative colitis, but the mechanism of action through the regulation of M1/M2 macrophage polarization has not been elaborated. The ulcerative colitis was modeled by dextran sulfate sodium; colitis mice were orally administrated with curcumin (10 mg/kg/day) or 5-ASA (300 mg/kg/day) for 14 consecutive days. After curcumin treatment, the body weight, colon weight and length, colonic weight index, and histopathological damage in colitis mice were effectively improved. The concentrations of proinflammatory cytokines IL-1β, IL-6, and CCL-2 in the colonic tissues of colitis mice decreased significantly, while anti-inflammatory cytokines IL-33 and IL-10 increased significantly. Importantly, macrophage activation was suppressed and M1/M2 macrophage polarization was regulated in colitis mice, and the percentage of CD11b⁺F4/80⁺ and CD11b⁺F4/80⁺TIM-1⁺ and CD11b⁺F4/80⁺iNOS⁺ decreased significantly and CD11b⁺F4/80⁺CD206⁺ and CD11b⁺F4/80⁺CD163⁺ increased significantly. Additionally, curcumin significantly downregulated CD11b⁺F4/80⁺TLR4⁺ macrophages and the protein levels of TLR2, TLR4, MyD88, NF-κBp65, p38MAPK, and AP-1 in colitis mice. Our study suggested that curcumin exerted therapeutic effects in colitis mice by regulating the balance of M1/M2 macrophage polarization and TLRs signaling pathway.

Role of hypothalamic-pituitary adrenal-axis, toll-like receptors, and macrophage polarization in pre-atherosclerotic changes induced by social isolation stress in mice

It has been well documented that chronic stress can induce atherosclerotic changes, however, the underlying mechanisms is yet to be established. In this regard, this study aimed to elucidate the relation between hypothalamic-pituitary adrenal-axis (HPA-axis), toll-like receptors (TLRs), as well as M1/M2 macrophage ratio and pre-atherosclerotic changes in social isolation stress (SIS) in mice. We used small interfering RNA against the glucocorticoid receptor (GR) to evaluate the relation between HPA-axis and TLRs. C57BL/6J mice were subjected to SIS and RT-PCR, ELISA, flow cytometry, and immunohistochemistry were used to assess the relations between pre-atherosclerotic changes and TLRs, macrophage polarization, pro-inflammatory cytokines, and cell adhesion molecules in aortic tissue. We used TAK-242 (0.3 mg/kg, intraperitoneally), a selective antagonist of TLR4, as a possible prophylactic treatment for atherosclerotic changes induced by SIS. We observed that isolated animals had higher serum concentration of corticosterone and higher body weight in comparison to normal animals. In isolated animals, results of in vitro study showed that knocking-down of the GR in bone marrow-derived monocytes significantly decreased the expression of TLR4. In vivo study suggested higher expression of TLR4 on circulating monocytes and higher M1/M2 ratio in aortic samples. Pathological study showed a mild pre-atherosclerotic change in isolated animals. Finally, we observed that treating animals with TAK-242 could significantly inhibit the pre-atherosclerotic changes. SIS can possibly increase the risk of atherosclerosis through inducing abnormal HPA-axis activity and subsequently lead to TLR4 up-regulation, vascular inflammation, high M1/M2 ratio in intima. Thus, TLR4 inhibitors might be a novel treatment to decrease the risk of atherosclerosis induced by chronic stress.

Comparison of individual and combination treatments with naproxen, prednisolone and hydroxychloroquine to treat Complete Freund's Adjuvant induced arthritis

Aim of this study was to evaluate and compare the efficacy of anti-arthritic drugs (naproxen, prednisolone, and hydroxychloroquine) alone and in combination. The in vitro anti-arthritic activity was evaluated by stabilization of human erythrocytes (HRBCs) membrane assays. In vivo activity was carried out using Complete Freund's Adjuvant (CFA) induced arthritic model in Wistar rat. Individual and combination drugs were administered for 21 days in rats 8 days post inoculation with CFA (0.15 ml injected in right hind paw). Body weight and paw edema were measured at different intervals. Combination treatments exhibited more HRBC stabilization than individual treatments. All individual and combination treatments reduced the level of C-reactive protein (CRP), liver function enzymes, malondialdehyde, white blood cells and platelets, with the most pronounced activity exhibited by the combination of three drugs. The level of oxidative stress biomarkers (reduced glutathione, catalase, and superoxide dismutase), red blood cells, and hemoglobin were notably increased in all treatment groups in contrasts to diseased control rats. Histopathological evaluation of the paw showed that all the treatments had reduced (p < 0.05-0.001) the arthritic indices in contrasts to diseased control rats. The serum concentrations of TNF-α and PGE2 were provoked in diseased control rats but had been notably (p < 0.0001) restored by treatments with individual and combination drugs. It was also found that combination treatments, more precisely triple drug was remarkably effective in treating arthritis. It can be concluded that naproxen, prednisolone, and hydroxychloroquine effectively ameliorated the CFA-induced arthritis and were more effective in combination as compared to individual drug therapy probably due to reduction in oxidative stress and inflammatory markers. Moreover, two lower doses (half NPH/2 and one-third NPH/3) of triple combination therapy naproxen, prednisolone, and hydroxychloroquine (NPH) showed no significant difference in anti-arthritic effect as compared to the highest dose level of NPH.

Proteoglycan-4 is an essential regulator of synovial macrophage polarization and inflammatory macrophage joint infiltration

BACKGROUND

Synovial macrophages perform a multitude of functions that include clearance of cell debris and foreign bodies, tissue immune surveillance, and resolution of inflammation. The functional diversity of macrophages is enabled by distinct subpopulations that express unique surface markers. Proteoglycan-4 (PRG4) is an important regulator of synovial hyperplasia and fibrotic remodeling, and the involvement of macrophages in PRG4's synovial role is yet to be defined. Our objectives were to study the PRG4's importance to macrophage homeostatic regulation in the synovium and infiltration of pro-inflammatory macrophages in acute synovitis and investigate whether macrophages mediated synovial fibrosis in Prg4 gene-trap (Prg4GT/GT) murine knee joints.

METHODS

Macrophage phenotyping in Prg4GT/GT and Prg4+/+ joints was performed by flow cytometry using pan-macrophage markers, e.g., CD11b, F4/80, and surface markers of M1 macrophages (CD86) and M2 macrophages (CD206). Characterizations of the various macrophage subpopulations were performed in 2- and 6-month-old animals. The expression of inflammatory markers, IL-6, and iNOS in macrophages that are CD86+ and/or CD206+ was studied. The impact of Prg4 recombination on synovial macrophage populations of 2- and 6-month-old animals and infiltration of pro-inflammatory macrophages in response to a TLR2 agonist challenge was determined. Macrophages were depleted using liposomal clodronate and synovial membrane thickness, and the expression of fibrotic markers α-SMA, PLOD2, and collagen type I (COL-I) was assessed using immunohistochemistry.

RESULTS

Total macrophages in Prg4GT/GT joints were higher than Prg4+/+ joints (p<0.0001) at 2 and 6 months, and the percentages of CD86+/CD206- and CD86+/CD206+ macrophages increased in Prg4GT/GT joints at 6 months (p<0.0001), whereas the percentage of CD86-/CD206+ macrophages decreased (p<0.001). CD86+/CD206- and CD86+/CD206+ macrophages expressed iNOS and IL-6 compared to CD86-/CD206+ macrophages (p<0.0001). Prg4 re-expression limited the accumulation of CD86+ macrophages (p<0.05) and increased CD86-/CD206+ macrophages (p<0.001) at 6 months. Prg4 recombination attenuated synovial recruitment of pro-inflammatory macrophages in 2-month-old animals (p<0.001). Clodronate-mediated macrophage depletion reduced synovial hyperplasia, α-SMA, PLOD2, and COL-I expressions in the synovium (p<0.0001).

CONCLUSIONS

PRG4 regulates the accumulation and homeostatic balance of macrophages in the synovium. In its absence, the synovium becomes populated with M1 macrophages. Furthermore, macrophages exert an effector role in synovial fibrosis in Prg4GT/GT animals.

Dehydrocostus Lactone Attenuates Methicillin-Resistant Staphylococcus aureus-Induced Inflammation and Acute Lung Injury via Modulating Macrophage Polarization

Dehydrocostus lactone (DHL), a natural sesquiterpene lactone isolated from the traditional Chinese herbs Saussurea lappa and Inula helenium L., has important anti-inflammatory properties used for treating colitis, fibrosis, and Gram-negative bacteria-induced acute lung injury (ALI). However, the effects of DHL on Gram-positive bacteria-induced macrophage activation and ALI remains unclear. In this study, we found that DHL inhibited the phosphorylation of p38 MAPK, the degradation of IκBα, and the activation and nuclear translocation of NF-κB p65, but enhanced the phosphorylation of AMP-activated protein kinase (AMPK) and the expression of Nrf2 and HO-1 in lipoteichoic acid (LTA)-stimulated RAW264.7 cells and primary bone-marrow-derived macrophages (BMDMs). Given the critical role of the p38 MAPK/NF-κB and AMPK/Nrf2 signaling pathways in the balance of M1/M2 macrophage polarization and inflammation, we speculated that DHL would also have an effect on macrophage polarization. Further studies verified that DHL promoted M2 macrophage polarization and reduced M1 polarization, then resulted in a decreased inflammatory response. An in vivo study also revealed that DHL exhibited anti-inflammatory effects and ameliorated methicillin-resistant Staphylococcus aureus (MRSA)-induced ALI. In addition, DHL treatment significantly inhibited the p38 MAPK/NF-κB pathway and activated AMPK/Nrf2 signaling, leading to accelerated switching of macrophages from M1 to M2 in the MRSA-induced murine ALI model. Collectively, these data demonstrated that DHL can promote macrophage polarization to an anti-inflammatory M2 phenotype via interfering in p38 MAPK/NF-κB signaling, as well as activating the AMPK/Nrf2 pathway in vitro and in vivo. Our results suggested that DHL might be a novel candidate for treating inflammatory diseases caused by Gram-positive bacteria.

Toll-Like Receptor 2 Antagonist Ameliorates Type 2 Diabetes Mellitus Associated Neuropathic Pain by Repolarizing Pro-inflammatory Macrophages

Diabetic neuropathy is one of the common complications of type 2 diabetes mellitus (T2DM) with severe outcomes. The mechanisms of physiopathology of diabetic neuropathy are not well elucidated. Inflammation and inflammatory macrophages are recognized to be crucial in diabetic neuropathy. Toll-like receptor 2 (TLR2) is an important factor in innate immune response which could promote the polarization of inflammatory macrophages. In present study, we evaluated the effects of a TLR2 antagonist CU-CPT22 on diabetic neuropathy. We induced T2DM in mice by feeding with high fat diet (HFD). We measured the body weight, blood glucose level, paw withdrawal threshold, inflammatory cytokine production, and macrophages infiltration in T2DM mice. We evaluated the effects of CU-CPT22 on pro-inflammatory cytokines production, macrophage marker expression in lipopolysaccharides (LPS)-treated BMDMs. We administrated CU-CPT22 in T2DM mice and measured the pro-inflammatory cytokines levels, expression of macrophages markers in sciatic nerve (SCN), and paw withdrawal threshold. T2DM mice had significantly increased body weight and blood glucose, and had significantly decreased paw withdrawal threshold. Obvious increased pro-inflammatory cytokine level and infiltration of M1 phenotype macrophages was observed in SCN from T2DM mice. CU-CPT22 prevented pro-inflammatory cytokine production in LPS-treated BMDMs and re-polarized them to M2 phenotype. CU-CPT22 suppressed the inflammation and induced M2 macrophages in SCN from T2DM mice, and ameliorated the paw withdrawal threshold in T2DM mice. CU-CPT22 ameliorates neuropathic pain in T2DM by promoting M2 phenotype macrophages.

Contribution of Toll-Like Receptors and the NLRP3 Inflammasome in Rheumatoid Arthritis Pathophysiology

Rheumatoid arthritis (RA) is a progressive autoimmune disease that is characterized by inflammation of the synovial joints leading to cartilage and bone damage. The pathogenesis is sustained by the production of pro-inflammatory cytokines including tumor necrosis factor (TNF), interleukin (IL)-1 and IL-6, which can be targeted therapeutically to alleviate disease severity. Several innate immune receptors are suggested to contribute to the chronic inflammation in RA, through the production of pro-inflammatory factors in response to endogenous danger signals. Much research has focused on toll-like receptors and more recently the nucleotide-binding domain and leucine-rich repeat pyrin containing protein-3 (NLRP3) inflammasome, which is required for the processing and release of IL-1β. This review summarizes the current understanding of the potential involvement of these receptors in the initiation and maintenance of inflammation and tissue damage in RA and experimental arthritis models.

Immunomodulation by Bifidobacterium animalis subsp. lactis Bb12: Integrative Analysis of miRNA Expression and TLR2 Pathway-Related Target Proteins in Swine Monocytes

Bifidobacterium animalis subsp. lactis Bb12 is a widely used probiotic that provides numerous health benefits to its host, many due to its immunomodulatory properties. Although the precise mechanism of modulation is still under investigation, several reports associate the interaction of TLR2 with components of the bacterial cell wall inducing a signaling cascade that culminates with the production of cytokines and co-stimulatory molecules. MicroRNAs (miRNAs) have emerged as important post-transcriptional regulators of immune responses, including those toward probiotics. In this study, we analyzed the miRNA expression profile in swine monocytes exposed to Bb12 by using an anti-TLR2 blocking strategy and Bb12 involvement in the regulation of the TLR2 pathway. As a result, the expression of 40 miRNAs was influenced by the treatments (p < 0.01), and 15 differentially expressed miRNAs with validated miRNA–mRNA interactions with around 26 proteins related to the TLR2 pathway were identified. The miRNAs upregulated in response to Bb12 included miR-15a-5p, miR-16-5p, miR-26a-5p, miR-29b-3p, and miR-30d-5p, and the following showed downregulation: miR-181a-5p, miR-19b-3p, miR-21-5p, miR-23a-5p, and miR-221-3p. The expression of let-7c-5p, let-7f-5p, miR-146b-5p, miR-150-5p, and miR-155-5p was increased by Bb12 only when TLR2 was blocked. The identified miRNA common targets were downstream proteins from bacterial recognition via TLR2, such as MyD88, TRAF6, and MAPK members; transcription factors such as NF-κB and AP-1; and cytokines such as IL-6, IL-10, and TNF-α. TLR2 participation was abrogated by anti-TLR2 antibody and suggests that bacterial recognition is complemented by other receptors since there were still changes in the microtranscriptome.

Nanomaterials Manipulate Macrophages for Rheumatoid Arthritis Treatment

Rheumatoid arthritis (RA) is a chronic, progressive, and systemic inflammatory autoimmune disease, characterized by synovial inflammation, synovial lining hyperplasia and inflammatory cell infiltration, autoantibody production, and cartilage/bone destruction. Macrophages are crucial effector cells in the pathological process of RA, which can interact with T, B, and fibroblast-like synovial cells to produce large amounts of cytokines, chemokines, digestive enzymes, prostaglandins, and reactive oxygen species to accelerate bone destruction. Therefore, the use of nanomaterials to target macrophages has far-reaching therapeutic implications for RA. A number of limitations exist in the current clinical therapy for patients with RA, including severe side effects and poor selectivity, as well as the need for frequent administration of therapeutic agents and high doses of medication. These challenges have encouraged the development of targeting drug delivery systems and their application in the treatment of RA. Recently, obvious therapeutic effects on RA were observed following the use of various types of nanomaterials to manipulate macrophages through intravenous injection (active or passive targeting), oral administration, percutaneous absorption, intraperitoneal injection, and intra-articular injection, which offers several advantages, such as high-precision targeting of the macrophages and synovial tissue of the joint. In this review, the mechanisms involved in the manipulation of macrophages by nanomaterials are analyzed, and the prospect of clinical application is also discussed. The objective of this article was to provide a reference for the ongoing research concerning the treatment of RA based on the targeting of macrophages.

Macrophages, as a Promising Strategy to Targeted Treatment for Colorectal Cancer Metastasis in Tumor Immune Microenvironment

The tumor immune microenvironment plays a vital role in the metastasis of colorectal cancer. As one of the most important immune cells, macrophages act as phagocytes, patrol the surroundings of tissues, and remove invading pathogens and cell debris to maintain tissue homeostasis. Significantly, macrophages have a characteristic of high plasticity and can be classified into different subtypes according to the different functions, which can undergo reciprocal phenotypic switching induced by different types of molecules and signaling pathways. Macrophages regulate the development and metastatic potential of colorectal cancer by changing the tumor immune microenvironment. In tumor tissues, the tumor-associated macrophages usually play a tumor-promoting role in the tumor immune microenvironment, and they are also associated with poor prognosis. This paper reviews the mechanisms and stimulating factors of macrophages in the process of colorectal cancer metastasis and intends to indicate that targeting macrophages may be a promising strategy in colorectal cancer treatment.

Metabolic Regulation of Macrophage Activation

Macrophages, the central mediators of innate immune responses, being in the first-line of defense, they have to readily respond to pathogenic or tissue damage signals to initiate the inflammatory cascade. Such rapid responses require energy to support orchestrated production of pro-inflammatory mediators and activation of phagocytosis. Being a cell type that is present in diverse environments and conditions, macrophages have to adapt to different nutritional resources. Thus, macrophages have developed plasticity and are capable of utilizing energy at both normoxic and hypoxic conditions and in the presence of varying concentrations of glucose or other nutrients. Such adaptation is reflected on changes in signaling pathways that modulate responses, accounting for the different activation phenotypes observed. Macrophage metabolism has been tightly associated with distinct activation phenotypes within the range of M1-like and M2-like types. In the context of diseases, systemic changes also affect macrophage metabolism, as in diabetes and insulin resistance, which results in altered metabolism and distinct activation phenotypes in the adipose tissue or in the periphery. In the context of solid tumors, tumor-associated macrophages adapt in the hypoxic environment, which results in metabolic changes that are reflected on an activation phenotype that supports tumor growth. Coordination of environmental and pathogenic signals determines macrophage metabolism, which in turn shapes the type and magnitude of the response. Therefore, modulating macrophage metabolism provides a potential therapeutic approach for inflammatory diseases and cancer.

Cytokine/Chemokine Release Patterns and Transcriptomic Profiles of LPS/IFNγ-Activated Human Macrophages Differentiated with Heat-Killed Mycobacterium obuense, M-CSF, or GM-CSF

Macrophages (Mφs) are instrumental regulators of the immune response whereby they acquire diverse functional phenotypes following their exposure to microenvironmental cues that govern their differentiation from monocytes and their activation. The complexity and diversity of the mycobacterial cell wall have empowered mycobacteria with potent immunomodulatory capacities. A heat-killed (HK) whole-cell preparation of Mycobacterium obuense (M. obuense) has shown promise as an adjunctive immunotherapeutic agent for the treatment of cancer. Moreover, HK M. obuense has been shown to trigger the differentiation of human monocytes into a monocyte-derived macrophage (MDM) type named Mob-MDM. However, the transcriptomic profile and functional properties of Mob-MDMs remain undefined during an activation state. Here, we characterized cytokine/chemokine release patterns and transcriptomic profiles of lipopolysaccharide (LPS)/interferon γ (IFNγ)-activated human MDMs that were differentiated with HK M. obuense (Mob-MDM(LPS/IFNγ)), macrophage colony-stimulating factor M-MDM(LPS/IFNγ)), or granulocyte/macrophage colony-stimulating factor (GM-MDM(LPS/IFNγ)). Mob-MDM(LPS/IFNγ) demonstrated a unique cytokine/chemokine release pattern (interleukin (IL)-10^low, IL-12/23p40^low, IL-23p19/p40^low, chemokine (C-x-C) motif ligand (CXCL)9^low) that was distinct from those of M-MDM(LPS/IFNγ) and GM-MDM(LPS/IFNγ). Furthermore, M-MDM(LPS/IFNγ) maintained IL-10 production at significantly higher levels compared to GM-MDM(LPS/IFNγ) and Mob-MDM(LPS/IFNγ) despite being activated with M1-Mφ-activating stimuli. Comparative RNA sequencing analysis pointed to a distinct transcriptome profile for Mob-MDM(LPS/IFNγ) relative to both M-MDM(LPS/IFNγ) and GM-MDM(LPS/IFNγ) that comprised 417 transcripts. Functional gene-set enrichment analysis revealed significant overrepresentation of signaling pathways and biological processes that were uniquely related to Mob-MDM(LPS/IFNγ). Our findings lay a foundation for the potential integration of HK M. obuense in specific cell-based immunotherapeutic modalities such as adoptive transfer of Mφs (Mob-MDM(LPS/IFNγ)) for cancer treatment.

ADP-heptose enables Helicobacter pylori to exploit macrophages as a survival niche by suppressing antigen-presenting HLA-II expression

The persistence of Helicobacter pylori in the human gastric mucosa implies that the immune response fails to clear the infection. We found that H. pylori compromises the antigen presentation ability of macrophages, because of the decline of the presenting molecules HLA-II. Here, we reveal that the main bacterial factor responsible for this effect is ADP-heptose, an intermediate metabolite in the biosynthetic pathway of lipopolysaccharide (LPS) that elicits a pro-inflammatory response in gastric epithelial cells. In macrophages, it upregulates the expression of miR146b which, in turn, would downmodulate CIITA, the master regulator for HLA-II genes. Hence, H. pylori, utilizing ADP-heptose, exploits a specific arm of macrophage response to establish its survival niche in the face of the immune defense elicited in the gastric mucosa.

Evaluation of immune status in testis and macrophage polarization associated with testicular damage in patients with nonobstructive azoospermia

OBJECTIVE

Immune cells residing in the testicular interstitial space form the immunological microenvironment of the testis. They are assumed to play a role in maintaining testicular homeostasis and immune privilege. However, the immune status and related cell polarization in patients with nonobstructive azoospermia (NOA) remains poorly characterized. System evaluation of the testis immunological microenvironment in NOA patients may help to reveal the mechanisms of idiopathic azoospermia.

STUDY DESIGN

The gene expression patterns of immune cells in normal human testes were systematically analyzed by single-cell RNA sequencing (scRNA-seq) and preliminarily verification by the human protein atlas (HPA) online database. The immune cell infiltration profiles and immune status of patients with NOA was analyzed by single-sample gene set enrichment analysis (ssGSEA) and gene set variation analysis (GSVA) based on four independent public microarray datasets (GSE45885, GSE45887, GSE9210, and GSE145467), obtained from Gene Expression Omnibus (GEO) online database. The relationship between immune cells and spermatogenesis score was further analyzed by Spearman correlation analysis. Finally, immunohistochemistry (IHC) staining was performed to identify the main immune cell types and their polarization status in patients with NOA.

RESULTS

Both scRNA-seq and HPA analysis showed that testicular macrophages represent the largest pool of immune cells in the normal testis, and also exhibit an attenuated inflammatory response by expressing high levels of tolerance proteins (CD163, IL-10, TGF-β, and VEGF) and reduced expression of TLR signaling pathway-related genes. Correlation analysis revealed that the testicular immune score and macrophages including M1 and M2 macrophages were significantly negatively correlated with spermatogenesis score in patients with NOA (GSE45885 and GSE45887). In addition, the number of M1 and M2 macrophages was significantly higher in patients with NOA (GSE9210 and GSE145467) than in normal testis. GSVA analysis indicated that the immunological microenvironment in NOA tissues was manifested by activated immune system and pro-inflammatory status. IHC staining results showed that the number of M1 and M2 macrophages was significantly higher in NOA tissues than in normal testis and negatively correlated with the Johnson score.

CONCLUSION

Testicular macrophage polarization may play a vital role in NOA development and is a promising potential therapeutic target.

Toll-like Receptor 2 in Autoimmune Inflammation

TLR signaling is critical for broad scale immune recognition of pathogens and/or danger molecules. TLRs are particularly important for the activation and the maturation of cells comprising the innate immune response. In recent years it has become apparent that several different TLRs regulate the function of lymphocytes as well, albeit to a lesser degree compared to innate immunity. TLR2 heterodimerizes with either TLR1 or TLR6 to broadly recognize bacterial lipopeptides as well as several danger-associated molecular patterns. In general, TLR2 signaling promotes immune cell activation leading to tissue inflammation, which is advantageous for combating an infection. Conversely, inappropriate or dysfunctional TLR2 signaling leading to an overactive inflammatory response could be detrimental during sterile inflammation and autoimmune disease. This review will highlight and discuss recent research advances linking TLR2 engagement to autoimmune inflammation.