Interferon-γ inhibits nonopsonized phagocytosis of macrophages via an mTORC1-c/EBPβ pathway

Serotonin Receptors in Myocardial Infarction: Friend or Foe?

Acute myocardial infarction (AMI) is one of the leading causes of death worldwide and treatment costs pose a major burden on the global health care system. Despite the variety of treatment options, individual recovery can be still poor and the mortality rate, especially in the first few years after the event, remains high. Therefore, intense research is currently focused on identifying novel target molecules to improve the outcome following AMI. One of the potentially interesting targets is the serotonergic system (5-HT system), not at least because of its connection to mental disorders. It is known that patients suffering from AMI have an increased risk of developing depression and vice versa. This implicates that the 5-HT system can be affected in response to AMI and might thus represent a target structure for patients' treatment. This review aims to highlight the importance of the 5-HT system after AMI by describing the role of individual serotonin receptors (5-HTR) in the regulation of physiological and pathophysiological responses. It particularly focuses on the signaling pathways of the serotonin receptors 1, 2, 4, and 7, which are expressed in the cardiovascular system, during disease onset, and the following remodeling process. This overview also emphasizes the importance of the 5-HT system in AMI etiology and highlights 5-HTRs as potential treatment targets.

Role of mTORC1 Signaling in Regulating the Immune Function of Granulocytes in Teleost Fish

Granulocytes are crucial innate immune cells that have been extensively studied in teleost fish. Studies in mammals have revealed that mechanistic target of rapamycin complex 1 (mTORC1) signaling acts as a significant immune regulatory hub, influencing granulocyte immune function. To investigate whether mTORC1 signaling also regulates the immune function of granulocytes in teleost fish, we established a model of RAPA inhibition of the mTORC1 signaling pathway using granulocytes from largemouth bass (Micropterus salmoides). Our results demonstrated that inhibition of mTORC1 signaling promoted autophagy and apoptosis of granulocytes while inhibiting cell proliferation. Moreover, inhibition of the mTORC1 signaling pathway enhanced the phagocytosis capacity of granulocytes. Collectively, our findings revealed the evolutionarily conserved role of the mTORC1 signaling pathway in regulating granulocyte responses, thus providing novel insights into the function of granulocytes in teleost fish.

Regulation of the phagocytic activity of astrocytes by neuroimmune mediators endogenous to the central nervous system

The phagocytic activity of glial cells is essential for maintaining normal brain activity, and its dysfunction may contribute to the central nervous system (CNS) pathologies, including neurodegenerative diseases. Phagocytic activity is one of the well-established neuroimmune functions of microglia. Although emerging evidence indicates that astrocytes can also function as CNS phagocytes in humans and rodents, limited information is available about the molecular mechanism regulating this function. To address this knowledge gap, we studied modulation of the phagocytic activity of human U118 MG astrocytic cells and murine primary astrocytes by four CNS inflammatory mediators and bacterial endotoxin lipopolysaccharide (LPS). LPS and cytochrome c (CytC) upregulated, while interferon (IFN)-γ downregulated, phagocytosis of latex beads by human astrocytic cells and phagocytosis of synaptosomes by murine primary astrocytes. Interleukin (IL)-1β and tumor necrosis factor (TNF)-α had no effect on the phagocytic activity of human astrocytic cells but upregulated this function in murine astrocytes. Varying effects of combinations of the above inflammatory mediators were observed in these two cell types. LPS- and CytC-induced phagocytic activity of human astrocytic cells was partially mediated by activation of toll-like receptor 4 (TLR4). By monitoring other functions of astrocytes, we concluded there were no correlations between the effects of the mediators studied on astrocyte phagocytic activity and their secretion of cytokines, cytotoxins, or glutamate. Our study identified four candidate CNS regulators of astrocyte phagocytic activity. Future investigation of molecular mechanisms behind this regulation could identify novel therapeutic targets allowing modulation of this astrocyte-mediated clearance mechanism in CNS pathologies.

CD4 T Cell-Dependent and -Independent Roles for IFN-γ in Blood-Stage Malaria

Production of IFN-γ by CD4 T cells is widely theorized to control Plasmodium parasite burden during blood-stage malaria. Surprisingly, the specific and crucial mechanisms through which this highly pleiotropic cytokine acts to confer protection against malarial disease remain largely untested in vivo. Here we used a CD4 T cell-restricted Cre-Lox IFN-γ excision mouse model to test whether and how CD4 T cell-derived IFN-γ controls blood-stage malaria. Although complete absence of IFN-γ compromised control of the acute and the chronic, recrudescent blood-stage infections with P. c. chabaudi, we identified a specific, albeit modest, role for CD4 T cell-derived IFN-γ in limiting parasite burden only during the chronic stages of P. c. chabaudi malaria. CD4 T cell IFN-γ promoted IgG Ab class switching to the IgG2c isotype during P. c. chabaudi malaria in C57BL/6 mice. Unexpectedly, our data do not support gross defects in phagocytic activity in IFN-γ-deficient hosts infected with blood-stage malaria. Together, our data confirm CD4 T cell-dependent roles for IFN-γ but suggest CD4 T cell-independent roles for IFN-γ in immune responses to blood-stage malaria.

Epithelial sodium channels in macrophage migration and polarization: role of proinflammatory cytokines TNFα and IFNγ

Migration of monocytes-macrophages plays an important role in phagocytosis of pathogens and cellular debris in a variety of pathophysiological conditions. Although epithelial Na+ channels (ENaCs) are required for normal migratory responses in other cell types, their role in macrophage migration signaling is unknown. To address this possibility, we determined whether ENaC message is present in several peripheral blood monocyte cell populations and tissue-resident macrophages in healthy humans using the Human Protein Atlas database (www.proteinatlas.org) and the mouse monocyte cell line RAW 264.7 using RT-PCR. We then determined that selective ENaC inhibition with amiloride inhibited chemotactic migration (∼50%), but not phagocytosis, of the mouse monocyte-macrophage cell line RAW 264.7. Furthermore, we generated a cell line stably expressing an NH2-terminal truncated αENaC to interrupt normal channel trafficking and found it suppressed migration. Prolonged exposure (48 h) of RAW 264.7 cells to proinflammatory cytokines interferon γ (IFNγ) and/or tumor necrosis factor α (TNFα) inhibited RAW 264.7 migration and abolished the amiloride (1 µM)-sensitive component of migration, a finding consistent with ENaC downregulation. To determine if proinflammatory cytokines regulate αENaC protein expression, cells were exposed to proinflammatory cytokines IFNγ (10 ng/mL, last 48 h) and TNFα (10 ng/mL, last 24 h). By Western blot analysis, we found whole cell αENaC protein is reduced ≥50%. Immunofluorescence demonstrated heterogeneous αENaC inhibition. Finally, we found that overnight exposure to amiloride stimulated morphological changes and increased polarization marker expression. Our findings suggest that ENaC may be a critical molecule in macrophage migration and polarization.

The Micro-Immunotherapy Medicine 2LEID Exhibits an Immunostimulant Effect by Boosting Both Innate and Adaptive Immune Responses

This study aimed at evaluating the effects of the micro-immunotherapy medicine (MIM) 2LEID, both in vitro and in vivo, on several components of the innate and adaptive immune system. MIM increased the phagocytic activity of macrophages, and it augmented the expression of the activation markers CD69 and HLA-DR in NK cells and monocytes/macrophages, respectively. The effect of MIM was evaluated in a model of respiratory infection induced by influenza A virus administration to immunocompetent mice in which it was able to improve neutrophil recruitment within the lungs (p = 0.1051) and slightly increased the circulating levels of IgM (p = 0.1655). Furthermore, MIM stimulated the proliferation of CD3-primed T lymphocytes and decreased the secretion of the immunosuppressive cytokine IL-10 in CD14⁺-derived macrophages. Human umbilical vein endothelial cells were finally used to explore the effect of MIM on endothelial cells, in which it slightly increased the expression of immune-related markers such as HLA-I, CD137L, GITRL, PD-L1 and ICAM-1. In conclusion, the present study suggests that MIM might be a promising nonspecific (without antigen specificity) immunostimulant drug in preventing and early treating respiratory infections, but not only exclusively, as it would gently support several facets of the immune system and host defenses.

Taurolithocholic acid but not tauroursodeoxycholic acid rescues phagocytosis activity of bone marrow-derived macrophages under inflammatory stress

Spinal cord injury (SCI) causes cell death and consequently the breakdown of axons and myelin. The accumulation of myelin debris at the lesion site induces inflammation and blocks axonal regeneration. Hematogenous macrophages contribute to the removal of myelin debris. In this study, we asked how the inflammatory state of macrophages affects their ability to phagocytose myelin. Bone marrow‐derived macrophages (BMDM) and Raw264.7 cells were stimulated with lipopolysaccharides (LPS) or interferon gamma (IFNγ), which induce inflammatory stress, and the endocytosis of myelin was examined. We found that activation of the TLR4‐NFκB pathway reduced myelin uptake by BMDM, while IFNγ‐Jak/STAT1 signaling did not. Since bile acids regulate lipid metabolism and in some cases reduce inflammation, our second objective was to investigate whether myelin clearance could be improved with taurolithocholic acid (TLCA), tauroursodeoxycholic acid or hyodeoxycholic acid. In BMDM only TLCA rescued myelin phagocytosis, when this activity was suppressed by LPS. Inhibition of protein kinase A blocked the effect of TLCA, while an agonist of the farnesoid X receptor did not rescue phagocytosis, implicating TGR5‐PKA signaling in the effect of TLCA. To shed light on the mechanism, we measured whether TLCA affected the expression of CD36, triggering receptor on myeloid cells‐2 (TREM2), and Gas6, which are known to be involved in phagocytosis and affected by inflammatory stimuli. Concomitant with an increase in expression of tumour necrosis factor alpha, LPS reduced expression of TREM2 and Gas6 in BMDM, and TLCA significantly diminished this downregulation. These findings suggest that activation of bile acid receptors may be used to improve myelin clearance in neuropathologies.

Interferon-gamma impairs phagocytosis of Escherichia coli by primary murine peritoneal macrophages stimulated with LPS and differentially modulates proinflammatory cytokine release

INTRODUCTION

Interferon-γ levels are increased upon viral infections and during inflamm-aging. Resistance to infections due to Escherichia coli (E. coli), a major cause of bacteriaemia and sepsis, is impaired in aged individuals, partly due to altered phagocytic capacity and cytokine release of immune cells. Here, we analyzed the effect of IFN-γ on phagocytosis of E. coli K1 and release of proinflammatory cytokines by macrophages in resting condition and upon stimulation with different bacterial Toll-like receptor (TLR) agonists.

METHODS

Primary peritoneal macrophages from C57BL/6 mice were exposed to medium or stimulated with agonists of TLR4 (LPS), 1/2 (Pam3CSK4), and 9 (CpG-DNA) in the presence and absence of IFN-γ (100 U/ml) for 24 h. TNF-α, IL-6, and KC were measured in the cell culture supernatant by ELISA. Macrophages were exposed to viable E. coli K1. After 90 min, intracellular phagozytosed bacteria were quantified by quantitative plating.

RESULTS

Macrophages treated with LPS 1 µg/ml in the presence of IFN-γ ingested more than 10-fold lower numbers of E. coli than macrophages treated with LPS alone. Phagocytosis of E. coli by macrophages in resting condition or upon stimulation with Pam3CSK4 or CpG was not significantly affected by IFN-γ. Cytokine release was differentially modulated by IFN-γ, with reduced KC release by TLR-stimulated macrophages in the presence of IFN-γ being the most striking effect.

CONCLUSIONS

In vitro, IFN-γ reduces the phagocytosis of E. coli by LPS-stimulated macrophages and differentially modulates cytokine release of macrophages activated by different bacterial TLR agonists. Elevated levels of IFN-γ might lead to reduced bacterial clearance and worse outcome of bacterial infections, e.g., in aged individuals and after viral infections and other inflammatory events.

In vivo Neutralization of Pro-inflammatory Cytokines During Secondary Streptococcus pneumoniae Infection Post Influenza A Virus Infection

An overt pro-inflammatory immune response is a key factor contributing to lethal pneumococcal infection in an influenza pre-infected host and represents a potential target for therapeutic intervention. However, there is a paucity of knowledge about the level of contribution of individual cytokines. Based on the predictions of our previous mathematical modeling approach, the potential benefit of IFN-γ- and/or IL-6-specific antibody-mediated cytokine neutralization was explored in C57BL/6 mice infected with the influenza A/PR/8/34 strain, which were subsequently infected with the Streptococcus pneumoniae strain TIGR4 on day 7 post influenza. While single IL-6 neutralization had no effect on respiratory bacterial clearance, single IFN-γ neutralization enhanced local bacterial clearance in the lungs. Concomitant neutralization of IFN-γ and IL-6 significantly reduced the degree of pneumonia as well as bacteremia compared to the control group, indicating a positive effect for the host during secondary bacterial infection. The results of our model-driven experimental study reveal that the predicted therapeutic value of IFN-γ and IL-6 neutralization in secondary pneumococcal infection following influenza infection is tightly dependent on the experimental protocol while at the same time paving the way toward the development of effective immune therapies.

Tuberculosis Infection in a Patient Treated With Nivolumab for Non-small Cell Lung Cancer: Case Report and Literature Review

Nivolumab (PD-1 inhibitor) and other immune checkpoint inhibitors are used primarily to promote reactivation of anti-tumor immunity. However, due to their generalized immunorestorative properties, these agents may also trigger an unusual spectrum of side-effects termed immune-related adverse events. In the case of the lung, pulmonary infiltrates in patients treated with the anti-PD-1 inhibitors, nivolumab, or pembrolizumab, especially patients with non-small cell lung cancer, can result from immune-related pneumonitis, which, until fairly recently was believed to be of non-infective origin. This, in turn, may result in progression and pseudo-progression of disease. An increasing body of evidence has, however, identified pulmonary tuberculosis as an additional type of anti-PD-1 therapy-associated, immune-related adverse event, seemingly as a consequence of excessive reactivation of immune responsiveness to latent Mycobacterium tuberculosis infection. The current case report describes a 56-year old Caucasian female who presented with microbiologically-confirmed tuberculosis infection while on nivolumab therapy for non-small cell lung cancer. Notably, the patient, seemingly the first described from the African Continent, had not received immunosuppressive therapy prior to the diagnosis of tuberculosis.

Coinfection With Influenza A Virus and Klebsiella oxytoca: An Underrecognized Impact on Host Resistance and Tolerance to Pulmonary Infections

Pneumonia is a world health problem and a leading cause of death, particularly affecting children and the elderly (1, 2). Bacterial pneumonia following infection with influenza A virus (IAV) is associated with increased morbidity and mortality but the mechanisms behind this phenomenon are not yet well-defined (3). Host resistance and tolerance are two processes essential for host survival during infection. Resistance is the host's ability to clear a pathogen while tolerance is the host's ability to overcome the impact of the pathogen as well as the host response to infection (4-8). Some studies have shown that IAV infection suppresses the immune response, leading to overwhelming bacterial loads (9-13). Other studies have shown that some IAV/bacterial coinfections cause alterations in tolerance mechanisms such as tissue resilience (14-16). In a recent analysis of nasopharyngeal swabs from patients hospitalized during the 2013-2014 influenza season, we have found that a significant proportion of IAV-infected patients were also colonized with Klebsiella oxytoca, a gram-negative bacteria known to be an opportunistic pathogen in a variety of diseases (17). Mice that were infected with K. oxytoca following IAV infection demonstrated decreased survival and significant weight loss when compared to mice infected with either single pathogen. Using this model, we found that IAV/K. oxytoca coinfection of the lung is characterized by an exaggerated inflammatory immune response. We observed early inflammatory cytokine and chemokine production, which in turn resulted in massive infiltration of neutrophils and inflammatory monocytes. Despite this swift response, the pulmonary pathogen burden in coinfected mice was similar to singly-infected animals, albeit with a slight delay in bacterial clearance. In addition, during coinfection we observed a shift in pulmonary macrophages toward an inflammatory and away from a tissue reparative phenotype. Interestingly, there was only a small increase in tissue damage in coinfected lungs as compared to either single infection. Our results indicate that during pulmonary coinfection a combination of seemingly modest defects in both host resistance and tolerance may act synergistically to cause worsened outcomes for the host. Given the prevalence of K. oxytoca detected in human IAV patients, these dysfunctional tolerance and resistance mechanisms may play an important role in the response of patients to IAV.

Interferon-γ acts as a regulator in the trade-off between phagocytosis and production performance in dwarf chickens

Background

Interferon-γ (IFN-γ) is critical for innate and adaptive immunity against viral and bacterial infections. IFN-γ reportedly affects the phagocytic ability of monocytes and macrophages as well as regulates pituitary function in humans and mice. The present study analyzed the impact of IFN-γ on monocyte and macrophage phagocytosis, production performance, and pituitary function in vivo and in vitro (in dwarf chickens). IFN-γ was injected into dwarf chickens through a vein, and then, the laying rate, average egg weight, and levels of follicle-stimulating hormone (FSH) and IFN-γ were measured in treatment and control groups. For the in vitro experiment, the pituitary tissues were supplemented with IFN-γ, and the mRNA expression levels of follicle-stimulating hormone beta subunit (FSH-β), interferon gamma receptor 1 (IFNGR1), and interferon gamma receptor 2 (IFNGR2) in the pituitary were assessed.

Results

Monocyte and macrophage phagocytosis product (PP) was decreased by IFN-γ treatment in a dose-dependent manner in vitro. In the in vivo experiment, the level of IFN-γ in the treatment group was higher than that in the control group at 7 d (P < 0.05), 14 d (P < 0.01), and 21 d (P < 0.01) post-injection. Compared with the control group, monocyte and macrophage PP was lower in the treatment group after injection (P < 0.01). The laying rate was higher in the treatment group than in the control group at 2 and 3 wk post-injection (P < 0.05). There was a significant difference between the treatment and control groups in the levels of FSH at 1, 3, 7, and 14 d post-injection (P < 0.01). In the in vitro experiment, increased mRNA expression levels of FSH-β, IFNGR1, and IFNGR2 were observed in the treatment group after stimulation with 100 U/mL IFN-γ for 24 h compared to those in the control group (P < 0.05).

Conclusions

IFN-γ inhibited the phagocytosis of monocytes and macrophages; up-regulated the mRNA expression levels of the FSH-β, IFNGR1, and IFNGR2; enhanced the secretion of FSH; and improved the laying rate. IFN-γ might be an important regulator in the trade-off between the immune effect and production performance in dwarf chickens.

Three macrophage subsets are identified in the uterus during early human pregnancy

Macrophages are crucial for a successful pregnancy, and malfunctions of decidual macrophages correlate with adverse pregnancy outcomes, such as spontaneous abortion and preeclampsia. Previously, decidual macrophages were often thought to be a single population. In the present study, we identified three decidual macrophage subsets, CCR2-CD11cLO (CD11c^low, ~80%), CCR2-CD11cHI (CD11c^high, ~5%), and CCR2+CD11cHI (CD11c^high, 10-15%), during the first trimester of human pregnancy by flow cytometry analysis. CCR2-CD11cLO macrophages are widely distributed in the decidua, while CCR2-CD11cHI and CCR2+CD11cHI macrophages are primarily detected close to extravillous trophoblast cells according to immunofluorescence staining. According to RNA sequencing bioinformatics analysis and in vitro functional studies, these three subsets of macrophages have different phagocytic capacities. CCR2+CD11cHI macrophages have pro-inflammatory characteristics, while the CCR2-CD11cHI population is suggested to be anti-oxidative and anti-inflammatory due to its high expression of critical heme metabolism-related genes, suggesting that these two subsets of macrophages maintain an inflammatory balance at the leading edge of trophoblast invasion to facilitate the clearance of pathogen infection as well as maintain the homeostasis of the maternal-fetal interface. The present study physiologically identifies three decidual macrophage subsets. Further clarification of the functions of these subsets will improve our understanding of maternal-fetal crosstalk in the maintenance of a healthy pregnancy.

CD5L Promotes M2 Macrophage Polarization through Autophagy-Mediated Upregulation of ID3

CD5L (CD5 molecule-like) is a secreted glycoprotein that controls key mechanisms in inflammatory responses, with involvement in processes such as infection, atherosclerosis, and cancer. In macrophages, CD5L promotes an anti-inflammatory cytokine profile in response to TLR activation. In the present study, we questioned whether CD5L is able to influence human macrophage plasticity, and drive its polarization toward any specific phenotype. We compared CD5L-induced phenotypic and functional changes to those caused by IFN/LPS, IL4, and IL10 in human monocytes. Phenotypic markers were quantified by RT-qPCR and flow cytometry, and a mathematical algorithm was built for their analysis. Moreover, we compared ROS production, phagocytic capacity, and inflammatory responses to LPS. CD5L drove cells toward a polarization similar to that induced by IL10. Furthermore, IL10- and CD5L-treated macrophages showed increased LC3-II content and colocalization with acidic compartments, thereby pointing to the enhancement of autophagy-dependent processes. Accordingly, siRNA targeting ATG7 in THP1 cells blocked CD5L-induced CD163 and Mer tyrosine kinase mRNA and efferocytosis. In these cells, gene expression profiling and validation indicated the upregulation of the transcription factor ID3 by CD5L through ATG7. In agreement, ID3 silencing reversed polarization by CD5L. Our data point to a significant contribution of CD5L-mediated autophagy to the induction of ID3 and provide the first evidence that CD5L drives macrophage polarization.

The Nuclear Receptor LXR Limits Bacterial Infection of Host Macrophages through a Mechanism that Impacts Cellular NAD Metabolism

Macrophages exert potent effector functions against invading microorganisms but constitute, paradoxically, a preferential niche for many bacterial strains to replicate. Using a model of infection by Salmonella Typhimurium, we have identified a molecular mechanism regulated by the nuclear receptor LXR that limits infection of host macrophages through transcriptional activation of the multifunctional enzyme CD38. LXR agonists reduced the intracellular levels of NAD⁺ in a CD38-dependent manner, counteracting pathogen-induced changes in macrophage morphology and the distribution of the F-actin cytoskeleton and reducing the capability of non-opsonized Salmonella to infect macrophages. Remarkably, pharmacological treatment with an LXR agonist ameliorated clinical signs associated with Salmonella infection in vivo, and these effects were dependent on CD38 expression in bone-marrow-derived cells. Altogether, this work reveals an unappreciated role for CD38 in bacterial-host cell interaction that can be pharmacologically exploited by activation of the LXR pathway.

Immunomodulators targeting MARCO expression improve resistance to postinfluenza bacterial pneumonia

Downregulation of the alveolar macrophage (AM) receptor with collagenous structure (MARCO) leads to susceptibility to postinfluenza bacterial pneumonia, a major cause of morbidity and mortality. We sought to determine whether immunomodulation of MARCO could improve host defense and resistance to secondary bacterial pneumonia. RNAseq analysis identified a striking increase in MARCO expression between days 9 and 11 after influenza infection and indicated important roles for Akt and Nrf2 in MARCO recovery. In vitro, primary human AM-like monocyte-derived macrophages (AM-MDMs) and THP-1 macrophages were treated with IFNγ to model influenza effects. Activators of Nrf2 (sulforaphane) or Akt (SC79) caused increased MARCO expression and a MARCO-dependent improvement in phagocytosis in IFNγ-treated cells and improved survival in mice with postinfluenza pneumococcal pneumonia. Transcription factor analysis also indicated a role for transcription factor E-box (TFEB) in MARCO recovery. Overexpression of TFEB in THP-1 cells led to marked increases in MARCO. The ability of Akt activation to increase MARCO expression in IFNγ-treated AM-MDMs was abrogated in TFEB-knockdown cells, indicating Akt increases MARCO expression through TFEB. Increasing MARCO expression by targeting Nrf2 signaling or the Akt-TFEB-MARCO pathway are promising strategies to improve bacterial clearance and survival in postinfluenza bacterial pneumonia.

Direct effects of airborne PM2.5 exposure on macrophage polarizations

BACKGROUND

Exposure of atmospheric particulate matter with an aerodynamic diameter less than 2.5μm (PM2.5) is epidemiologically associated with illnesses. Potential effects of air pollutants on innate immunity have raised concerns. As the first defense line, macrophages are able to induce inflammatory response. However, whether PM2.5 exposure affects macrophage polarizations remains unclear.

METHODS

We used freshly isolated macrophages as a model system to demonstrate effects of PM2.5 on macrophage polarizations. The expressions of cytokines and key molecular markers were detected by real-time PCR, and flow cytometry. The specific inhibitors and gene deletion technologies were used to address the molecular mechanisms.

RESULTS

PM2.5 increased the expression of pro-inflammatory cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-6 (IL-6), interleukin-1β (IL-1β), tumor necrosis factor alpha (TNFα). PM2.5 also enhanced the lipopolysaccharide (LPS)-induced M1 polarization even though there was no evidence in the change of cell viability. However, PM2.5 significantly decreased the number of mitochondria in a dose dependent manner. Pre-treatment with NAC, a scavenger of reactive oxygen species (ROS), prevented the increase of ROS and rescued the PM2.5-impacted M1 but not M2 response. However, mTOR deletion partially rescued the effects of PM2.5 to reduce M2 polarization.

CONCLUSIONS

PM2.5 exposure significantly enhanced inflammatory M1 polarization through ROS pathway, whereas PM2.5 exposure inhibited anti-inflammatory M2 polarization through mTOR-dependent pathway.

GENERAL SIGNIFICANCE

The present studies suggested that short-term exposure of PM2.5 acts on the balance of inflammatory M1 and anti-inflammatory M2 macrophage polarizations, which may be involved in air pollution-induced immune disorders and diseases. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.