Targeting Macrophage Polarization in Infectious Diseases: M1/M2 Functional Profiles, Immune Signaling and Microbial Virulence Factors

INTRODUCTION

An event of increasing interest during host-pathogen interactions is the polarization of patrolling/naive monocytes (MOs) into macrophage subsets (MФs). Therapeutic strategies aimed at modulating this event are under investigation.

METHODS

This review focuses on the mechanisms of induction/development and profile of MФs polarized toward classically proinflammatory (M1) or alternatively anti-inflammatory (M2) phenotypes in response to bacteria, fungi, parasites, and viruses.

RESULTS AND DISCUSSION

It highlights nuclear, cytoplasmic, and cell surface receptors (pattern recognition receptors/PPRs), microenvironmental mediators, and immune signaling. MФs polarize into phenotypes: M1 MФs, activated by IFN-γ, pathogen-associated molecular patterns (PAMPs, e.g. lipopolysaccharide) and membrane-bound PPRs ligands (TLRs/CLRs ligands); or M2 MФs, induced by interleukins (ILs-4, -10 and -13), antigen-antibody complexes, and helminth PAMPs. Polarization toward M1 and M2 profiles evolve in a pathogen-specific manner, with or without canonicity, and can vary widely. Ultimately, this can result in varying degrees of host protection or more severe disease outcome. On the one hand, the host is driving effective MФs polarization (M1 or M2); but on the other hand, microorganisms may skew the polarization through virulence factors to increase pathogenicity. Cellular/genomic reprogramming also ensures plasticity of M1/M2 phenotypes. Because modulation of polarization can occur at multiple points, new insights and emerging perspectives may have clinical implications during the inflammation-to-resolution transition; translated into practical applications as for therapeutic/vaccine design target to boost microbicidal response (M1, e.g. triggering oxidative burst) with specifics PAMPs/IFN-γ or promote tissue repair (M2, increasing arginase activity) via immunotherapy.

Orientia tsutsugamushi Ank5 promotes NLRC5 cytoplasmic retention and degradation to inhibit MHC class I expression

How intracellular bacteria subvert the major histocompatibility complex (MHC) class I pathway is poorly understood. Here, we show that the obligate intracellular bacterium Orientia tsutsugamushi uses its effector protein, Ank5, to inhibit nuclear translocation of the MHC class I gene transactivator, NLRC5, and orchestrate its proteasomal degradation. Ank5 uses a tyrosine in its fourth ankyrin repeat to bind the NLRC5 N-terminus while its F-box directs host SCF complex ubiquitination of NLRC5 in the leucine-rich repeat region that dictates susceptibility to Orientia- and Ank5-mediated degradation. The ability of O. tsutsugamushi strains to degrade NLRC5 correlates with ank5 genomic carriage. Ectopically expressed Ank5 that can bind but not degrade NLRC5 protects the transactivator during Orientia infection. Thus, Ank5 is an immunoevasin that uses its bipartite architecture to rid host cells of NLRC5 and reduce surface MHC class I molecules. This study offers insight into how intracellular pathogens can impair MHC class I expression.

RTP4 restricts lyssavirus rabies infection by binding to viral genomic RNA

Rabies, caused by lyssavirus rabies (Rabies lyssavirus, RABV), is a fatal disease among humans and almost all warm-blooded animals. In this study, we found that RABV infection induces the up-regulation of receptor transporter protein 4 (RTP4) in mouse brains and different cells of nervous tissue. Over-expression of RTP4 reduces the viral titer of RABV in different neuronal cells. Furthermore, a recombinant RABV expressing RTP4, named rRABV-RTP4, was constructed and displayed a lower viral titer in different neuronal cells due to the expression of RTP4. Moreover, the survival rates of mice infected with rRABV-RTP4 were significantly higher than those of mice infected with parent virus rRABV or control virus rRABV-RTP4(-). In terms of mechanism, RTP4 could bind viral genomic RNA (vRNA) of RABV, and suppress the whole viral genome amplification. In addition, we found that the zinc finger domain (ZFD) of RTP4 exerts the antiviral function by truncation analysis, and an important amino acids site (C95) in the RTP4 3CxxC motif which is essential for its antiviral function was identified by mutation analysis. This study contributes to our understanding of how RTP4 or other RTP proteins play a role in defense against the invasion of RABV or other viruses.

ALKBH5 modulates macrophages polarization in tumor microenvironment of ovarian cancer

BACKGROUND

Macrophages play an essential role in regulating ovarian cancer immune microenvironment. Studies have shown that m6A methylation could influence immune microenvironment in cancer. In this study, we investigated the roles of m6A demethylase ALKBH5 and m6A recognition protein IGF2BP2 played in regulating macrophages polarization in ovarian cancer.

METHODS

In this study, we first explored the differentially expressed m6A methylation enzymes in M0 and M2 macrophages according to two independent GEO datasets. TIMER2.0 and GSCA database were used to explore the immune analysis of ALKBH5 and IGF2BP2 in ovarian cancer. K-M plotter and TIMER2.0 databases were used to evaluate the prognostic role of ALKBH5 and IGF2BP2 in ovarian cancer. For CNV mutation analysis of ALKBH5 and IGF2BP2, cBioPortal and GSCA databases were used. For single-cell analysis, sc-TIME and HPA softwares were used to analyze the roles of ALKBH5 and IGF2BP2 played in immune cells in ovarian cancer. To identify the role of ALKBH5 played in macrophage polarization, RT-PCR was used to verify the macrophage polarization related markers in vitro study. The function of ALKBH5 played in ovarian cancer was further analyzed through GO and KEGG analysis.

FINDINGS

In this study, we found that ALKBH5 and IGF2BP2 were up-regulated in M2 macrophages, which showed closely correlation with immune cells expressions in ovarian cancer, especially with macrophages. Ovarian cancer patients with higher expression of ALKBH5 and IGF2BP2 showed worse prognosis, possibly because of their close correlation with immune response. ALKBH5 also correlated with macrophage phenotypes in single-cell levels analysis. However, the expression level of IGF2BP2 in ovarian cancer immune microenvironment was very low. The results of RT-PCR indicated the potential role of ALKBH5 in M2 polarization of macrophages.

INTERPRETATION

ALKBH5 participated in regulating macrophage M2 polarization in ovarian cancer immune microenvironment.

Primary Murine Macrophages as a Tool for Virulence Factor Discovery in Coxiella burnetii

Coxiella burnetii requires a type IVB secretion system (T4SS) to promote intracellular replication and virulence. We hypothesized that Coxiella employs its T4SS to secrete effectors that enable stealthy colonization of immune cells. To address this, we used RNA sequencing to compare the transcriptional response of murine bone marrow-derived macrophages (BMDM) infected with those of wild-type Coxiella and a T4SS-null mutant at 8 and 24 h postinfection. We found a T4SS-independent upregulation of proinflammatory transcripts which was consistent with a proinflammatory polarization phenotype. Despite this, infected BMDM failed to completely polarize, as evidenced by modest surface expression of CD38 and CD11c, nitrate production, and reduced proinflammatory cytokine and chemokine secretion compared to positive controls. As these BMDM permitted replication of C. burnetii, we employed them to identify T4SS effectors that are essential in the specific cellular context of a primary macrophage. We found five Himar1 transposon mutants in T4SS effectors that had a replication defect in BMDM but not J774A.1 cells. The mutants were also attenuated in a SCID mouse model of infection. Among these candidate virulence factors, we found that CBU1639 contributed to the inhibition of macrophage proinflammatory responses to Coxiella infection. These data demonstrate that while T4SS is dispensable for the stealthy invasion of primary macrophages, Coxiella has evolved multiple T4SS effectors that specifically target macrophage function to proliferate within that specific cellular context. IMPORTANCE Coxiella burnetii, the causative agent of Q fever, preferentially infects macrophages of the respiratory tract when causing human disease. This work describes how primary macrophages respond to C. burnetii at the earliest stages of infection, before bacterial replication. We found that while infected macrophages increase expression of proinflammatory genes after bacterial entry, they fail to activate the accompanying antibacterial functions that might ultimately control the infection. This disconnect between initial response and downstream function was not mediated by the bacterium's type IVB secretion system, suggesting that Coxiella has other virulence factors that dampen host responses early in the infection process. Nevertheless, we were able to identify several type IVB secreted effectors that were specifically required for survival in macrophages and mice. This work is the first to identify type IVB secretion effectors that are specifically required for infection and replication within primary macrophages.

RegEnrich gene regulator enrichment analysis reveals a key role of the ETS transcription factor family in interferon signaling

Changes in a few key transcriptional regulators can lead to different biological states. Extracting the key gene regulators governing a biological state allows us to gain mechanistic insights. Most current tools perform pathway/GO enrichment analysis to identify key genes and regulators but tend to overlook the gene/protein regulatory interactions. Here we present RegEnrich, an open-source Bioconductor R package, which combines differential expression analysis, data-driven gene regulatory network inference, enrichment analysis, and gene regulator ranking to identify key regulators using gene/protein expression profiling data. By benchmarking using multiple gene expression datasets of gene silencing studies, we found that RegEnrich using the GSEA method to rank the regulators performed the best. Further, RegEnrich was applied to 21 publicly available datasets on in vitro interferon-stimulation of different cell types. Collectively, RegEnrich can accurately identify key gene regulators from the cells under different biological states, which can be valuable in mechanistically studying cell differentiation, cell response to drug stimulation, disease development, and ultimately drug development.

Natural genetic variation in Drosophila melanogaster reveals genes associated with Coxiella burnetii infection

The gram-negative bacterium Coxiella burnetii is the causative agent of Query (Q) fever in humans and coxiellosis in livestock. Host genetics are associated with C. burnetii pathogenesis both in humans and animals; however, it remains unknown if specific genes are associated with severity of infection. We employed the Drosophila Genetics Reference Panel to perform a genome-wide association study to identify host genetic variants that affect host survival to C. burnetii infection. The genome-wide association study identified 64 unique variants (P < 10⁻⁵) associated with 25 candidate genes. We examined the role each candidate gene contributes to host survival during C. burnetii infection using flies carrying a null mutation or RNAi knockdown of each candidate. We validated 15 of the 25 candidate genes using at least one method. This is the first report establishing involvement of many of these genes or their homologs with C. burnetii susceptibility in any system. Among the validated genes, FER and tara play roles in the JAK/STAT, JNK, and decapentaplegic/TGF-β signaling pathways which are components of known innate immune responses to C. burnetii infection. CG42673 and DIP-ε play roles in bacterial infection and synaptic signaling but have no previous association with C. burnetii pathogenesis. Furthermore, since the mammalian ortholog of CG13404 (PLGRKT) is an important regulator of macrophage function, CG13404 could play a role in host susceptibility to C. burnetii through hemocyte regulation. These insights provide a foundation for further investigation regarding the genetics of C. burnetii susceptibility across a wide variety of hosts.

Avoidance of the NLRP3 Inflammasome by the Stealth Pathogen, Coxiella burnetii

Coxiella burnetii, a highly adapted obligate intracellular bacterial pathogen and the cause of the zoonosis Q fever, is a reemerging public health threat. C. burnetii employs a Type IV secretion system (T4SS) to establish and maintain its intracellular niche and modulate host immune responses including the inhibition of apoptosis. Interactions between C. burnetii and caspase-1-mediated inflammasomes are not fully elucidated. This study confirms that C. burnetii does not activate caspase-1 during infection of mouse macrophages in vitro. C. burnetii-infected cells did not develop NLRP3 and ASC foci indicating its ability to avoid cytosolic detection. C. burnetii is unable to inhibit the pyroptosis and IL-1β secretion that is induced by potent inflammasome stimuli but rather enhances these caspase-1-mediated effects. We found that C. burnetii upregulates pro-IL-1β and robustly primes NLRP3 inflammasomes via TLR2 and MyD88 signaling. As for wildtype C. burnetii, T4SS-deficient mutants primed and potentiated NLRP3 inflammasomes. An in vivo model of pulmonary infection in C57BL/6 mice was developed. Mice deficient in NLRP3 or caspase-1 were like wildtype mice in the development and resolution of splenomegaly due to red pulp hyperplasia, and histologic lesions and macrophage kinetics, but had slightly higher pulmonary bacterial burdens at the greatest measured time point. Together these findings indicate that C. burnetii primes but avoids cytosolic detection by NLRP3 inflammasomes, which are not required for the clinical resistance of C57BL/6 mice. Determining mechanisms employed by C. burnetii to avoid cytosolic detection via NLRP3 inflammasomes will be beneficial to the development of preventative and interventional therapies for Q fever.

Revealing nuclear receptor hub modules from Basal-like breast cancer expression networks

Nuclear receptors are a class of transcriptional factors. Together with their co-regulators, they regulate development, homeostasis, and metabolism in a ligand-dependent manner. Their ability to respond to environmental stimuli rapidly makes them versatile cellular components. Their coordinated activities regulate essential pathways in normal physiology and in disease. Due to their complexity, the challenge remains in understanding their direct associations in cancer development. Basal-like breast cancer is an aggressive form of breast cancer that often lacks ER, PR and Her2. The absence of these receptors limits the treatment for patients to the non-selective cytotoxic and cytostatic drugs. To identify potential drug targets it is essential to identify the most important nuclear receptor association network motifs in Basal-like subtype progression. This research aimed to reveal the transcriptional network patterns, in the hope to capture the underlying molecular state driving Basal-like oncogenesis. In this work, we illustrate a multidisciplinary approach of integrating an unsupervised machine learning clustering method with network modelling to reveal unique transcriptional patterns (network motifs) underlying Basal-like breast cancer. The unsupervised clustering method provides a natural stratification of breast cancer patients, revealing the underlying heterogeneity in Basal-like. Identification of gene correlation networks (GCNs) from Basal-like patients in both the TCGA and METABRIC databases revealed three critical transcriptional regulatory constellations that are enriched in Basal-like. These represent critical NR components implicated in Basal-like breast cancer transcription. This approach is easily adaptable and applicable to reveal critical signalling relationships in other diseases.

Tumor-associated macrophage polarization promotes the progression of esophageal carcinoma

The immune response facilitated by tumor-associated macrophages is a vital determinant of tumor progression. We identified differentially expressed genes between various macrophage phenotypes in the Gene Expression Omnibus, and used Kaplan-Meier Plotter to determine which of them altered the prognosis of esophageal carcinoma patients. Fibrinogen-like protein 2 (FGL2), an immunosuppressive factor in the tumor microenvironment of various cancers, was upregulated in M2 macrophages, and higher FGL2 expression was associated with poorer survival in esophageal carcinoma patients. Using the TIMER database, we found that FGL2 expression correlated positively with the levels of immune markers of infiltrating B cells, CD8+ T cells, CD4+ T cells, macrophages, neutrophils and dendritic cells in esophageal carcinoma samples. Correlation analyses in cBioPortal revealed that the mRNA levels of FGL2 correlated strongly with those of interleukin 10, matrix metalloproteinase 9, C-C motif chemokine ligand 5, T-cell immunoglobulin mucin 3, interleukin 13, vascular cell adhesion molecule 1, macrophage colony-stimulating factor and fibroblast growth factor 7 in esophageal carcinoma tissues. The same cytokines were upregulated when esophageal squamous cell carcinoma cells were co-cultured with M2-like tumor-associated macrophages. Thus, by secreting FGL2, M2-like tumor-associated macrophages may create an immunosuppressive tumor microenvironment that induces the occurrence and progression of esophageal carcinoma.

Transcriptomics uncovers substantial variability associated with alterations in manufacturing processes of macrophage cell therapy products

Gene expression plasticity is central for macrophages' timely responses to cues from the microenvironment permitting phenotypic adaptation from pro-inflammatory (M1) to wound healing and tissue-regenerative (M2, with several subclasses). Regulatory macrophages are a distinct macrophage type, possessing immunoregulatory, anti-inflammatory, and angiogenic properties. Due to these features, regulatory macrophages are considered as a potential cell therapy product to treat clinical conditions, e.g., non-healing diabetic foot ulcers. In this study we characterized two differently manufactured clinically relevant regulatory macrophages, programmable cells of monocytic origin and comparator macrophages (M1, M2a and M0) using flow-cytometry, RT-qPCR, phagocytosis and secretome measurements, and RNA-Seq. We demonstrate that conventional phenotyping had a limited potential to discriminate different types of macrophages which was ameliorated when global transcriptome characterization by RNA-Seq was employed. Using this approach we confirmed that macrophage manufacturing processes can result in a highly reproducible cell phenotype. At the same time, minor changes introduced in manufacturing resulted in phenotypically and functionally distinct regulatory macrophage types. Additionally, we have identified a novel constellation of process specific biomarkers, which will support further clinical product development.

Emerging translation strategies during virus-host interaction

Translation control is crucial during virus-host interaction. On one hand, viruses completely rely on the protein synthesis machinery of host cells to propagate and have evolved various mechanisms to redirect the host's ribosomes toward their viral mRNAs. On the other hand, the host rewires its translation program in an attempt to contain and suppress the virus early on during infection; the antiviral program includes specific control on protein synthesis to translate several antiviral mRNAs involved in quenching the infection. As the infection progresses, host translation is in turn inhibited in order to limit viral propagation. We have learnt of very diverse strategies that both parties utilize to gain or retain control over the protein synthesis machinery. Yet novel strategies continue to be discovered, attesting for the importance of mRNA translation in virus-host interaction. This review focuses on recently described translation strategies employed by both hosts and viruses. These discoveries provide additional pieces in the understanding of the complex virus-host translation landscape. This article is categorized under: Translation > Translation Mechanisms Translation > Translation Regulation.

Emerging Roles for NLRC5 in Immune Diseases

Innate immunity activates the corresponding immune response relying on multiple pattern recognition receptors (PRRs) that includes pattern recognition receptors (PRRs), like NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and C-type lectin receptors (CLRs), which could accurately recognize invasive pathogens. In particular, NLRs belong to a large protein family of pattern recognition receptors in the cytoplasm, where they are highly correlated with activation of inflammatory response system followed by rapid clearance of invasive pathogens. Among the NLRs family, NLRC5, also known as NOD4 or NOD27, accounts for a large proportion and involves in immune responses far and wide. Notably, in the above response case of inflammation, the expression of NLRC5 remarkably increased in immune cells and immune-related tissues. However, the evidence for higher expression of NLRC5 in immune disease still remains controversial. It is noted that the growing evidence further accounts for the participation of NLRC5 in the innate immune response and inflammatory diseases. Moreover, NLRC5 has also been confirmed to exert a critical role in the control of regulatory diverse signaling pathways. Together with its broad participation in the occurrence and development of immune diseases, NLRC5 can be consequently treated as a potential therapeutic target. Nevertheless, the paucity of absolute understanding of intrinsic characteristics and underlying mechanisms of NLRC5 still make it hard to develop targeting drugs. Therefore, current summary about NLRC5 information is indispensable. Herein, current knowledge of NLRC5 is summarized, and research advances in terms of NLRC5 in characteristics, biological function, and regulatory mechanisms are reviewed.

Identification of new molecular targets for PET imaging of the microglial anti-inflammatory activation state

Microglia are potential targets for therapeutic intervention in neurological and neurodegenerative diseases affecting the central nervous system. In order to assess the efficacy of therapies aimed to reduce the tissue damaging activities of microglia and/or to promote the protective potential of these cells, suitable pre-clinical and clinical tools for the in vivo analysis of microglia activities and dynamics are required. The aim of this work was to identify new translational markers of the anti-inflammatory / protective state of microglia for the development of novel PET tracers.

Methods: New translational markers of the anti-inflammatory/protective activation state of microglia were selected by bioinformatic approaches and were in vitro and ex vivo validated by qPCR and immunohistochemistry in rodent and human samples. Once a viable marker was identified, a novel PET tracer was developed. This tracer was subsequently confirmed by autoradiography experiments in murine and human brain tissues.

Results: Here we provide evidence that P2RY12 expression increases in murine and human microglia following exposure to anti-inflammatory stimuli, and that its expression is modulated in the reparative phase of experimental and clinical stroke. We then synthesized a novel carbon-11 labeled tracer targeting P2RY12, showing increased binding in brain sections of mice treated with IL4, and low binding to brain sections of a murine stroke model and of a stroke patient.

Conclusion: This study provides new translational targets for PET tracers for the anti-inflammatory/protective activation state of microglia and shows the potential of a rationale-based approach. It therefore paves the way for the development of novel non-invasive methodologies aimed to monitor the success of therapeutic approaches in various neurological diseases.

Regulation of an Opioid Receptor Chaperone Protein, RTP4, by Morphine

Signaling by classic analgesics, such as morphine, is governed primarily by the relative abundance of opioid receptors at the cell surface, and this is regulated by receptor delivery to, and retrieval from, the plasma membrane. Although retrieval mechanisms, such as receptor endocytosis, have been extensively investigated, fewer studies have explored mechanisms of receptor maturation and delivery to the plasma membrane. A previous study implicated receptor transporter proteins (RTPs) in the latter process. Since not much is known about regulation of RTP expression, we initiated studies examining the effect of chronic morphine administration on the levels of RTPs in the brain. Among the four RTPs, we detected selective and region-specific changes in RTP4 expression; RTP4 mRNA is significantly upregulated in the hypothalamus compared with other brain regions. We examined whether increased RTP4 expression impacted receptor protein levels and found a significant increase in the abundance of mu opioid receptors (MOPrs) but not other related G protein-coupled receptors (GPCRs, such as delta opioid, CB₁ cannabinoid, or D₂ dopamine receptors) in hypothalamic membranes from animals chronically treated with morphine. Next, we used a cell culture system to show that RTP4 expression is necessary and sufficient for regulating opioid receptor abundance at the cell surface. Interestingly, selective MOPr-mediated increase in RTP4 expression leads to increases in cell surface levels of MOPr-delta opioid receptor heteromers, and this increase is significantly attenuated by RTP4 small interfering RNA. Together, these results suggest that RTP4 expression is regulated by chronic morphine administration, and this, in turn, regulates opioid receptor cell surface levels and function.

Effect of Polarization and Chronic Inflammation on Macrophage Expression of Heparan Sulfate Proteoglycans and Biosynthesis Enzymes

Heparan sulfate (HS) proteoglycans on immune cells have the ability to bind to and regulate the bioactivity more than 400 bioactive protein ligands, including many chemokines, cytokines, and growth factors. This makes them important regulators of the phenotype and behavior of immune cells. Here we review how HS biosynthesis in macrophages is regulated during polarization and in chronic inflammatory diseases such as rheumatoid arthritis, atherosclerosis, asthma, chronic obstructive pulmonary disease and obesity, by analyzing published micro-array data and mechanistic studies in this area. We describe that macrophage expression of many HS biosynthesis and core proteins is strongly regulated by macrophage polarization, and that these expression patterns are recapitulated in chronic inflammation. Such changes in HS biosynthetic enzyme expression are likely to have a significant impact on the phenotype of macrophages in chronic inflammatory diseases by altering their interactions with chemokines, cytokines, and growth factors.

MALDI-TOF MS monitoring of PBMC activation status in sepsis

Background

MALDI-TOF mass spectrometry (MS) on whole cells enables the detection of different cell types and cell activation. Here, we wondered whether this approach would be useful to investigate the host response in sepsis.

Methods

Peripheral blood mononuclear cells (PBMCs) from patients with severe sepsis and healthy donors were analyzed with MALDI-TOF MS. PBMCs from healthy donors were also stimulated with lipopolysaccharide, peptidoglycan, CpG oligonucleotides, polyinosinic polycytidylic acid, and with heat-inactivated bacteria. Averaged spectra of PBMCs stimulated in vitro by different agonists were generated from the database using the Biotyper software and matching scores between each spectrum from patients and averaged spectra from the database were calculated.

Results

We show that the MALDI-TOF MS signature of PBMCs from septic patients was specific, compared with healthy controls. As the fingerprints observed in patients may be related to PBMC activation, PBMCs from healthy controls were stimulated with cytokines, soluble Pathogen-Associated Molecular Patterns (PAMPs) and heat-killed bacteria, and we created a database of reference spectra. The MALDI-TOF MS profiles of PBMCs from septic patients were then compared with the database. No differences were found between patients with documented infection (n = 6) and those without bacteriological documentation (n = 6). The spectra of PBMCs from septic patients matched with those of interferon-γ- and interleukin-10-stimulated PBMCs, confirming that sepsis is characterized by both inflammatory and immunoregulatory features. Interestingly, the spectra of PBMCs from septic patients without documented infection matched with the reference spectrum of PBMCs stimulated by CpG oligonucleotides, suggesting a bacterial etiology in these patients.

Conclusions

Despite the limits of this preliminary study, these results indicate that the monitoring of functional status of PBMCs in peripheral blood by whole cell MALDI-TOF MS could provide unique opportunities to assess disease progression or resolution in clinical settings.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3266-7) contains supplementary material, which is available to authorized users.

Cigarette smoke extract interferes with placenta macrophage functions: A new mechanism to compromise placenta functions?

The success of pregnancy depends on the maternal immune system's ability to promote tolerance and host defense. This equilibrium is compromised in inflammatory and infectious impairment of placenta. Smoking during pregnancy exposes the fetus to severe complications which might result from an alteration in placenta macrophages (pMφ) functions. In this study, we assessed the effect of cigarette smoke extract (CSE) on the functions of third trimester pMφs.CSE inhibited particles uptake and the formation of multinucleated giant cells, a recently reported property of pMφs based on their ability to fuse in vitro. These alterations were associated with a CSE-induced abnormal activation of pMφs, which was characterized by an increased release of TNF, interleukin (IL)-33, and decreased IL-6 and IL-10 release. Furthermore, CSE enhanced the expression of metalloproteinase genes known to be involved in tissue remodeling. This effect of CSE on pMφs was specific because CSE affected circulating monocytes in a different way. Finally, we showed that nicotine affected in part the functional properties of pMφs. Taken together, these results showed that CSE modulated the functional activity of pMφs, which may compromise pregnancy.

Deconvolution of heterogeneous wound tissue samples into relative macrophage phenotype composition via models based on gene expression

Macrophages, the primary cell of the innate immune system, act on a spectrum of phenotypes that correspond to diverse functions. Dysregulation of macrophage phenotype is associated with many diseases. In particular, defective transition from pro-inflammatory (M1) to anti-inflammatory (M2) behavior has been implicated as a potential source of sustained inflammation that prevents healing of chronic wounds such as diabetic ulcers. In order to design effective treatments, an understanding of the relative presence of macrophage phenotypes during tissue repair is necessary. Inferring the relative phenotype composition is currently challenging due to the heterogeneous nature of the macrophages themselves and also of tissue samples. We propose here a method to deconvolute gene expression from heterogeneous tissue samples into the composition of two primary macrophage phenotypes (M1 and M2). Our final method uses gene expression signatures for each phenotype cultivated in vitro as input to a predictive model that infers sample composition with an average error of 0.16, and whose predictions fit known compositions prepared in vitro with an R² value of 0.90. Finally, we apply this model to describe macrophage behavior in human diabetic ulcer healing using clinically isolated ulcer tissue samples. The model predicted that non-healing diabetic ulcers contained higher proportions of M1 macrophages compared to healing diabetic ulcers, in agreement with numerous studies that have implicated a dysfunctional M1-to-M2 transition in the impaired healing of diabetic ulcers. These results show proof of concept that the model holds utility in making predictions regarding macrophage behavior in heterogeneous samples, with potential application as a wound healing diagnostic.

Murine Alveolar Macrophages Are Highly Susceptible to Replication of Coxiella burnetii Phase II In Vitro

Coxiella burnetii is a Gram-negative bacterium that causes Q fever in humans. Q fever is an atypical pneumonia transmitted through inhalation of contaminated aerosols. In mammalian lungs, C. burnetii infects and replicates in several cell types, including alveolar macrophages (AMs). The innate immunity and signaling pathways operating during infection are still poorly understood, in part because of the lack of relevant host cell models for infection in vitro In the study described here, we investigated and characterized the infection of primary murine AMs by C. burnetii phase II in vitro Our data reveal that AMs show a pronounced M2 polarization and are highly permissive to C. burnetii multiplication in vitro Murine AMs present an increased susceptibility to infection in comparison to primary bone marrow-derived macrophages. AMs support more than 2 logs of bacterial replication during 12 days of infection in culture, similar to highly susceptible host cells, such as Vero and THP-1 cells. As a proof of principle that AMs are useful for investigation of C. burnetii replication, we performed experiments with AMs from Nos2(-/-) or Ifng(-/-) mice. In the absence of gamma interferon and nitric oxide synthase 2 (NOS2), AMs were significantly more permissive than wild-type cells. In contrast, AMs from Il4(-/-) mice were more restrictive to C. burnetii replication, supporting the importance of M2 polarization for the permissiveness of AMs to C. burnetii replication. Collectively, our data account for understanding the high susceptibility of alveolar macrophages to bacterial replication and support the use of AMs as a relevant model of C. burnetii growth in primary macrophages.

The plasma levels of soluble ST2 as a marker of gut mucosal damage in early HIV infection

OBJECTIVE

Following tissue barrier breaches, interleukin-33 (IL-33) is released as an 'alarmin' to induce inflammation. Soluble suppression of tumorigenicity 2 (sST2), as an IL-33 decoy receptor, contributes to limit inflammation. We assessed the relationship between the IL-33/ST2 axis and markers of gut mucosal damage in patients with early (EHI) and chronic HIV infection (CHI) and elite controllers.

DESIGN

Analyses on patients with EHI and CHI were conducted to determine IL-33/sST2 changes over time.

METHODS

IL-33 and sST2 levels were measured in plasma. Correlations between sST2 levels and plasma viral load, CD4 and CD8 T-cell counts, expression of T-cell activation/exhaustion markers, gut mucosal damage, microbial translocation and inflammation markers, as well as kynurenine/tryptophan ratio were assessed.

RESULTS

Plasma sST2 levels were elevated in EHI compared with untreated CHI and uninfected controls, whereas IL-33 levels were comparable in all groups. In EHI, sST2 levels were positively correlated with the CD8 T-cell count and the percentage of T cells expressing activation and exhaustion markers, but not with viral load or CD4 T-cell count. Plasma sST2 levels also correlated with plasma levels of gut mucosal damage, microbial translocation and kynurenine/tryptophan ratio and for some markers of inflammation. Prospective analyses showed that early antiretroviral therapy had no impact on sST2 levels, whereas longer treatment duration initiated during CHI normalized sST2.

CONCLUSION

As sST2 levels were elevated in EHI and were correlated with CD8 T-cell count, immune activation, and microbial translocation, sST2 may serve as a marker of disease progression, gut damage and may directly contribute to HIV pathogenesis.

Integrated Transcriptomics Establish Macrophage Polarization Signatures and have Potential Applications for Clinical Health and Disease

Growing evidence defines macrophages (Mφ) as plastic cells with wide-ranging states of activation and expression of different markers that are time and location dependent. Distinct from the simple M1/M2 dichotomy initially proposed, extensive diversity of macrophage phenotypes have been extensively demonstrated as characteristic features of monocyte-macrophage differentiation, highlighting the difficulty of defining complex profiles by a limited number of genes. Since the description of macrophage activation is currently contentious and confusing, the generation of a simple and reliable framework to categorize major Mφ phenotypes in the context of complex clinical conditions would be extremely relevant to unravel different roles played by these cells in pathophysiological scenarios. In the current study, we integrated transcriptome data using bioinformatics tools to generate two macrophage molecular signatures. We validated our signatures in in vitro experiments and in clinical samples. More importantly, we were able to attribute prognostic and predictive values to components of our signatures. Our study provides a framework to guide the interrogation of macrophage phenotypes in the context of health and disease. The approach described here could be used to propose new biomarkers for diagnosis in diverse clinical settings including dengue infections, asthma and sepsis resolution.

Immune Suppression by Myeloid Cells in HIV Infection: New Targets for Immunotherapy

Over thirty years of extensive research has not yet solved the complexity of HIV pathogenesis leading to a continued need for a successful cure. Recent immunotherapy-based approaches are aimed at controlling the infection by reverting immune dysfunction. Comparatively less appreciated than the role of T cells in the context of HIV infection, the myeloid cells including macrophages monocytes, dendritic cells (DCs) and neutrophils contribute significantly to immune dysfunction. Host restriction factors are cellular proteins expressed in these cells which are circumvented by HIV. Guided by the recent literature, the role of myeloid cells in HIV infection will be discussed highlighting potential targets for immunotherapy. HIV infection, which is mainly characterized by CD4 T cell dysfunction, also manifests in a vicious cycle of events comprising of inflammation and immune activation. Targeting the interaction of programmed death-1 (PD-1), an important regulator of T cell function; with PD-L1 expressed mainly on myeloid cells could bring promising results. Macrophage functional polarization from pro-inflammatory M1 to anti-inflammatory M2 and vice versa has significant implications in viral pathogenesis. Neutrophils, recently discovered low density granular cells, myeloid derived suppressor cells (MDSCs) and yolk sac macrophages provide new avenues of research on HIV pathogenesis and persistence. Recent evidence has also shown significant implications of neutrophil extracellular traps (NETs), antimicrobial peptides and opsonizing antibodies. Further studies aimed to understand and modify myeloid cell restriction mechanisms have the potential to contribute in the future development of more effective anti-HIV interventions that may pave the way to viral eradication.

Modulation of monocyte subsets in infectious diseases

Monocytes are effector immune cells but a precise analysis of their role in immune response has been precluded by their heterogeneity. Indeed, human monocytes are composed of at least three different subsets with different phenotypic characteristics and functional properties, the so-called classical, intermediate and non-classical monocytes. A review of the literature shows that these monocyte subsets are differently affected during viral, bacterial, parasitic and fungal infections. The expansion of the CD16⁺ compartment (intermediate and non-classical monocytes) is typically observed in the majority of infectious diseases and the increased proportion of CD16⁺ monocytes is likely related to their activation through their direct interaction with the pathogen or the inflammatory context. In contrast, the number of non-classical and intermediate monocytes is decreased in Q fever endocarditis, suggesting that complex mechanisms govern the equilibrium among monocyte subsets. The measurement of monocyte subsets would be useful in better understanding of the role of monocyte activation in the pathophysiology of infectious diseases.

Transcriptomic profiling facilitates classification of response to influenza challenge

Abstract

Despite increases in vaccination coverage, reductions in influenza-related mortality have not been observed. Better vaccines are therefore required and influenza challenge studies can be used to test the efficacy of new vaccines. However, this requires the accurate post-challenge classification of subjects by outcome, which is limited in current methods that use artificial thresholds to assign ‘symptomatic’ and ‘asymptomatic’ phenotypes. We present data from an influenza challenge study in which 22 healthy adults (11 vaccinated) were inoculated with H3N2 influenza (A/Wisconsin/67/2005). We generated genome-wide gene expression data from peripheral blood taken immediately before the challenge and at 12, 24 and 48 h post-challenge. Variation in symptomatic scoring was found amongst those with laboratory confirmed influenza. By combining the dynamic transcriptomic data with the clinical parameters this variability can be reduced. We identified four subjects with severe laboratory confirmed influenza that show differential gene expression in 1103 probes 48 h post-challenge compared to the remaining subjects. We have further reduced this profile to six genes (CCL2, SEPT4, LAMP3, RTP4, MT1G and OAS3) that can be used to define these subjects. We have used this gene set to predict symptomatic infection from an independent study. This analysis gives further insight into host-pathogen interactions during influenza infection. However, the major potential value is in the clinical trial setting by providing a more quantitative method to better classify symptomatic individuals post influenza challenge.

Key message

Differential gene expression signatures are seen following influenza challenge.

Expression of six predictive genes can classify response to influenza challenge.

The genomic influenza response classification replicates in an independent dataset.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-014-1212-8) contains supplementary material, which is available to authorized users.

Phenotypic diversity and emerging new tools to study macrophage activation in bacterial infectious diseases

Macrophage polarization is a concept that has been useful to describe the different features of macrophage activation related to specific functions. Macrophage polarization is responsible for a dichotomic approach (killing vs. repair) of the host response to bacteria; M1-type conditions are protective, whereas M2-type conditions are associated with bacterial persistence. The use of the polarization concept to classify the features of macrophage activation in infected patients using transcriptional and/or molecular data and to provide biomarkers for diagnosis and prognosis has most often been unsuccessful. The confrontation of polarization with different clinical situations in which monocytes/macrophages encounter bacteria obliged us to reappraise this concept. With the exception of M2-type infectious diseases, such as leprosy and Whipple's disease, most acute (sepsis) or chronic (Q fever, tuberculosis) infectious diseases do not exhibit polarized monocytes/macrophages. This is also the case for commensals that shape the immune response and for probiotics that alter the immune response independent of macrophage polarization. We propose that the type of myeloid cells (monocytes vs. macrophages) and the kinetics of the immune response (early vs. late responses) are critical variables for understanding macrophage activation in human infectious diseases. Explorating the role of these new markers will provide important tools to better understand complex macrophage physiology.