Macrophage polarization and bacterial infections

A Negative Feedback Loop Between Autophagy and Immune Responses in Mycobacterium leprae Infection

The obligate intracellular bacterium Mycobacterium leprae is the causative agent of leprosy and primarily infects macrophages, leading to irreversible nerve damage and deformities. So far, the underlying reasons allowing M. leprae to persist and propagate in macrophages, despite the presence of cellular immunity, are still a mystery. Here, we investigated the role of autophagy, a cellular process that degrades cytosolic materials and intracellular pathogens, in M. leprae infection. We found that live M. leprae infection of macrophages resulted in significantly elevated autophagy level. However, macrophages with high autophagy levels preferentially expressed lower levels of proinflammatory cytokines, including interleukin (IL)-1β, IL-6, IL-12, and tumor necrosis factor-α, and preferentially primed anti-inflammatory T cells responses, characterized by high IL-10 and low interferon-γ, granzyme B, and perforin responses. These anti-inflammatory T cells could suppress further induction of autophagy, leading to improved survival of intracellular M. leprae in infected macrophages. Therefore, these data demonstrated that although autophagy had a role in eliminating intracellular pathogens, the induction of autophagy resulted in anti-inflammatory immune responses, which suppressed autophagy in a negative feedback loop and allowed the persistence of M. leprae.

Diabetic Wounds Exhibit Decreased Ym1 and Arginase Expression with Increased Expression of IL-17 and IL-20

Objective: Impaired wound healing in diabetic (DB) patients is a significant health problem; however, the roles that cytokines and innate immune cells contribute to this impaired healing are not completely understood. Approach: A mouse model was used to compare the innate immune response during DB and normal wound healing. Two 5-mm full-thickness wounds were created on the dorsal skin of BKS.Cg-m+/+Leprdb/J (DB) and C57BL/6 (wild-type) mice. Innate immune cell markers and cytokine mRNA levels were measured in wound biopsies during the first week of healing. Results: Innate immune cell influx (typified by the Gr-1 neutrophil marker and the Ym1 macrophage marker) was delayed in the DB wounds. Expression of the M2 macrophage-related genes, Ym1 and arginase 1, was significantly reduced in the DB wounds. PCR array analysis demonstrated altered cytokine expression in DB wounds. Most prominently, both interleukin (IL)-17 and IL-20 mRNA levels were significantly increased in the DB wounds. Innovation: This is the first study to identify increased levels of IL-17 and IL-20 in DB wounds. These cytokines are also elevated in the inflammatory skin disorder, psoriasis; thus, they may be potential therapeutic targets to aid in DB wound healing. Conclusion: The entire cytokine profile of DB wounds over the course of healing is not completely understood. This study suggests that the IL-17 and IL-20 families of cytokines should be further analyzed in the context of DB wound healing.

Jagged1 Instructs Macrophage Differentiation in Leprosy

As circulating monocytes enter the site of disease, the local microenvironment instructs their differentiation into tissue macrophages (MΦ). To identify mechanisms that regulate MΦ differentiation, we studied human leprosy as a model, since M1-type antimicrobial MΦ predominate in lesions in the self-limited form, whereas M2-type phagocytic MΦ are characteristic of the lesions in the progressive form. Using a heterotypic co-culture model, we found that unstimulated endothelial cells (EC) trigger monocytes to become M2 MΦ. However, biochemical screens identified that IFN-γ and two families of small molecules activated EC to induce monocytes to differentiate into M1 MΦ. The gene expression profiles induced in these activated EC, when overlapped with the transcriptomes of human leprosy lesions, identified Jagged1 (JAG1) as a potential regulator of MΦ differentiation. JAG1 protein was preferentially expressed in the lesions from the self-limited form of leprosy, and localized to the vascular endothelium. The ability of activated EC to induce M1 MΦ was JAG1-dependent and the addition of JAG1 to quiescent EC facilitated monocyte differentiation into M1 MΦ with antimicrobial activity against M. leprae. Our findings indicate a potential role for the IFN-γ-JAG1 axis in instructing MΦ differentiation as part of the host defense response at the site of disease in human leprosy.

Mycobacterial diseases, such as leprosy, continue to be serious causes of mortality and morbidity worldwide. They pose a unique treatment challenge due to their ability to modify the immune response in infected individuals. For example, in leprosy there are two distinct manifestations of the disease, each characterized by the immune response of the individual. One results in a more disseminated and severe form of the disease, lepromatous leprosy, and the other is a more limited form with marked antimicrobial activity, tuberculoid leprosy. These differences in the immune response can be characterized by the phenotype and activation state of the macrophage. We illustrate how the local endothelial microenvironment can “educate” macrophages, identifying Jagged1 and select small molecules that can regulate this pathway. Therefore, these studies identify a potential strategy to intervene in infection and inflammation, by targeting macrophage instruction at the site of disease. Through the integration of in vitro modeling and gene expression profiles at the site of disease, we found that Jagged 1 harnesses the endothelial microenvironment to instruct antimicrobial macrophage responses in leprosy.

Microbial metabolite butyrate facilitates M2 macrophage polarization and function

Metabolites from intestinal microbes modulate the mucosal immune system by regulating the polarization and expansion of T cells. Whether the microbial metabolites influence macrophage polarization, however, is poorly understood. Here, we show that the large bowel microbial fermentation product, butyrate, facilitates M2 macrophage polarization, in vitro and in vivo. The supernatant from butyrate-treated M2 macrophage increased the migration and enhanced the wound closure rate of MLE-12 cells. Butyrate attenuated intestinal inflammation in mice with dextran sulfate sodium (DSS)-induced colitis, with a significant increase in colonic expression of the M2 macrophage-associated protein, Arg1. M2 macrophage treated with butyrate, had increased activation of the H3K9/STAT6 signaling pathway, suggesting a mechanism for butyrate facilitated M2 macrophage polarization. Collectively, our study indicated that commensal microbe-derived butyrate is a novel activator of STAT6-mediated transcription through H3K9 acetylation driving M2 macrophage polarization, and delineated new insights into the immune interplay underlying inflammatory bowel disease.

Mycobacterium leprae alters classical activation of human monocytes in vitro

Background

Macrophages play a central role in the pathogenesis of leprosy, caused by Mycobacterium leprae. The polarized clinical presentations in leprosy are associated with differential immune activation. In tuberculoid leprosy, macrophages show a classical activation phenotype (M1), while macrophages in lepromatous disease display characteristics of alternative activation (M2). Bacille Calmette-Guérin (BCG) vaccination, which protects against leprosy, can promote sustained changes in monocyte response to unrelated pathogens and may preferentially direct monocytes towards an M1 protective phenotype. We previously reported that M. leprae can dampen the response of naïve human monocytes to a strong inducer of pro-inflammatory cytokines, such as BCG. Here, we investigated the ability of the pathogen to alter the direction of macrophage polarization and the impact of BCG vaccination on the monocyte response to M. leprae.

Findings

We show that in vitro exposure of monocytes from healthy donors to M. leprae interferes with subsequent M1 polarization, indicated by lower levels of M1-associated cytokine/chemokines released and reduced expression of M1 cell surface markers. Exposure to M. leprae phenolic glycolipid (PGL) 1, instead of whole bacteria, demonstrated a similar effect on M1 cytokine/chemokine release. In addition, we found that monocytes from 10-week old BCG-vaccinated infants released higher levels of the pro-inflammatory cytokines TNF-α and IL-1β in response to M. leprae compared to those from unvaccinated infants.

Conclusion

Exposure to M. leprae has an inhibitory effect on M1 macrophage polarization, likely mediated through PGL-1. By directing monocyte/macrophages preferentially towards M1 activation, BCG vaccination may render the cells more refractory to the inhibitory effects of subsequent M. leprae infection.

Dynamic macrophage polarization-specific miRNA patterns reveal increased soluble VEGF receptor 1 by miR-125a-5p inhibition

Dynamic, epigenetic mechanisms can regulate macrophage phenotypes following exposure to different stimulating conditions and environments. However, temporal patterns of microRNAs (miRNAs or miRs) across multiple macrophage polarization phenotypes have not been defined. We determined miRNA expression in bone marrow-derived murine macrophages over multiple time points (0.5, 1, 3, 24 h) following exposure to cytokines and/or LPS. We hypothesized that dynamic changes in miRNAs regulate macrophage phenotypes. Changes in macrophage polarization markers were detected as early as 0.5 and as late as 24 h; however, robust responses for most markers occurred within 3 h. In parallel, many polarization-specific miRNAs were also changed by 3 h and expressed divergent patterns between M1 and M2a conditions, with increased expression in M1 (miR-155, 199a-3p, 214-3p, 455-3p, and 125a) or M2a (miR-511 and 449a). Specifically, miR-125a-5p exhibited divergent patterns: increased at 12-24 h in M1 macrophages and decreasing trend in M2a. VEGF in the culture media of macrophages was dependent upon the polarization state, with greatly diminished VEGF in M2a compared with M1 macrophage culture media despite similar VEGF in cell lysates. Inhibition of miR-125a-5p in media-only controls (MO) and M1 macrophages greatly increased expression and secretion of soluble VEGF receptor-1 (sVEGFR1) leading to diminished VEGF in the culture media, partially converting MO and M1 into an M2a phenotype. Thus, the divergent expression patterns of polarization-specific miRNAs led to the identification and demonstrated the regulation of a specific macrophage polarization phenotype, sVEGFR1 by inhibition of miR-125a-5p.

Mycobacterium leprae-Infected Macrophages Preferentially Primed Regulatory T Cell Responses and Was Associated with Lepromatous Leprosy

BACKGROUND

The persistence of Mycobacterium leprae (M. leprae) infection is largely dependent on the types of host immune responses being induced. Macrophage, a crucial modulator of innate and adaptive immune responses, could be directly infected by M. leprae. We therefore postulated that M. leprae-infected macrophages might have altered immune functions.

METHODOLOGY/PRINCIPAL FINDINGS

Here, we treated monocyte-derived macrophages with live or killed M. leprae, and examined their activation status and antigen presentation. We found that macrophages treated with live M. leprae showed committed M2-like function, with decreased interleukin 1 beta (IL-1beta), IL-6, tumor necrosis factor alpha (TNF-alpha) and MHC class II molecule expression and elevated IL-10 and CD163 expression. When incubating with naive T cells, macrophages treated with live M. leprae preferentially primed regulatory T (Treg) cell responses with elevated FoxP3 and IL-10 expression, while interferon gamma (IFN-gamma) expression and CD8+ T cell cytotoxicity were reduced. Chromium release assay also found that live M. leprae-treated macrophages were more resistant to CD8+ T cell-mediated cytotoxicity than sonicated M. leprae-treated monocytes. Ex vivo studies showed that the phenotype and function of monocytes and macrophages had clear differences between L-lep and T-lep patients, consistent with the in vitro findings.

CONCLUSIONS/SIGNIFICANCE

Together, our data demonstrate that M. leprae could utilize infected macrophages by two mechanisms: firstly, M. leprae-infected macrophages preferentially primed Treg but not Th1 or cytotoxic T cell responses; secondly, M. leprae-infected macrophages were more effective at evading CD8+ T cell-mediated cytotoxicity.

Mechanism of Action of Probiotic Bacteria on Intestinal and Systemic Immunities and Antigen-Presenting Cells

Immunomodulation has been shown to be one of the major functions of probiotic bacteria. This review is presented to provide detailed information on the immunomodulatory properties of probiotics in various animal models and clinical practices. Probiotics can regulate helper T (Th) responses and release of cytokines in a strain-specific manner. For example, Lactobacillus rhamnosus GG can induce beneficial Th1 immunomodulatory effect in infants with cow's milk allergy and relieve intestinal inflammation in atopic children by promoting IL-10 generation. Mechanism of action of probiotics on antigen-presenting cells at gastrointestinal tract is also postulated in this review. Probiotic bacterial cells and their soluble factors may activate dendritic cells, macrophages, and to certain extent monocytes via toll-like-receptor recognition and may further provoke specific Th responses. They are speculated to elicit immunomodulatory effects on intestinal and systemic immunities.

Correlation between nerve growth factor and tissue expression of IL-17 in leprosy

Leprosy is a serious public health problem in peripheral and developing countries. Leprosy is a chronic infectious-contagious disease caused by the intracellular, bacillus Mycobacterium leprae, which causes tissue damage and demyelination of peripheral nerves. Recent studies have demonstrated the participation of new subtype's cytokines profile in the inflammatory response of leprosy. Since nerve functions are affected by inflammatory response during the course of leprosy, changes in the production of NGF and its receptor (NGF R) may be directly associated with disability and sensory loss. Skin biopsies were collected and submitted to immunohistochemistry using specific antibodies to IL-17, NGF and NGF R. Quantitative analysis of NGF, NGFR and IL-17 immunostaining showed a significant difference between the clinical forms, with higher expression of NGF and NGFR in lepromatous leprosy and IL-17 in tuberculoid leprosy. The present study showed that IL-17, in addition to stimulating an inflammatory response, negatively regulates the action of NGF and NGF R in the polar forms of the disease.

Transcriptional and Linkage Analyses Identify Loci that Mediate the Differential Macrophage Response to Inflammatory Stimuli and Infection

Macrophages display flexible activation states that range between pro-inflammatory (classical activation) and anti-inflammatory (alternative activation). These macrophage polarization states contribute to a variety of organismal phenotypes such as tissue remodeling and susceptibility to infectious and inflammatory diseases. Several macrophage- or immune-related genes have been shown to modulate infectious and inflammatory disease pathogenesis. However, the potential role that differences in macrophage activation phenotypes play in modulating differences in susceptibility to infectious and inflammatory disease is just emerging. We integrated transcriptional profiling and linkage analyses to determine the genetic basis for the differential murine macrophage response to inflammatory stimuli and to infection with the obligate intracellular parasite Toxoplasma gondii. We show that specific transcriptional programs, defined by distinct genomic loci, modulate macrophage activation phenotypes. In addition, we show that the difference between AJ and C57BL/6J macrophages in controlling Toxoplasma growth after stimulation with interferon gamma and tumor necrosis factor alpha mapped to chromosome 3, proximal to the Guanylate binding protein (Gbp) locus that is known to modulate the murine macrophage response to Toxoplasma. Using an shRNA-knockdown strategy, we show that the transcript levels of an RNA helicase, Ddx1, regulates strain differences in the amount of nitric oxide produced by macrophage after stimulation with interferon gamma and tumor necrosis factor. Our results provide a template for discovering candidate genes that modulate macrophage-mediated complex traits.

Macrophages provide a first line of defense against invading pathogens and play an important role in the initiation and resolution of immune responses. When in contact with pathogens or immune factors, such as cytokines, macrophages assume activation states that range between pro-inflammatory (classical activation) and anti-inflammatory (alternative activation). Even though it is known that macrophages from different individuals are biased towards one of the various activation states, the genetic factors that define individual differences in macrophage activation are not fully understood. Additionally, although macrophages are important in infectious disease pathogenesis, how individual differences in macrophage activation contribute to individual differences in susceptibility to infectious disease is just emerging. We used macrophages from genetically segregating mice to show that discrete transcriptional programs, which are modulated by specific genomic regions, modulate differences in macrophage activation. Murine macrophages differences in controlling Toxoplasma growth mapped to chromosome 3, proximal to the Guanylate binding protein (Gbp) locus that is known to modulate the murine macrophage response to Toxoplasma. Using a shRNA-mediated knockdown approach, we show that the DEAD box polypeptide 1 (Ddx1) modulates nitric oxide production in macrophages stimulated with interferon gamma and tumor necrosis factor. These findings are a step towards the identification of genes that regulate macrophage phenotypes and disease outcome.

A protective effect of the laminated layer on Echinococcus granulosus survival dependent on upregulation of host arginase

The role of nitric oxide (NO) in host defense against Echinococcus granulosus larvae was previously reported. However, NO production by NOS2 (inducible NO synthase) is counteracted by the expression of Arginase. In the present study, our aim is to evaluate the involvement of the laminated layer (external layer of parasitic cyst) in Arginase induction and the protoscoleces (living and infective part of the cyst) survival. Our in vitro results indicate that this cystic compound increases the Arginase activity in macrophages. Moreover, C-type lectin receptors (CLRs) with specificity for mannan and the TGF-β are implicated in this effect as shown after adding Mannan and Anti-TGFβ. Interestingly, the laminated layer increases protoscoleces survival in macrophages-parasite co-cultures. Our results indicate that the laminated layer protects E. granulosus against the NOS2 protective response through Arginase pathway, a hallmark of M2 macrophages.

Neisseria gonorrhoeae Modulates Immunity by Polarizing Human Macrophages to a M2 Profile

Current data suggest that Neisseria gonorrhoeae is able to suppress the protective immune response at different levels, such as B and T lymphocytes and antigen-presenting cells. The present report is focused on gonococcus evasion mechanism on macrophages (MФ) and its impact in the subsequent immune response. In response to various signals MФ may undergo classical-M1 (M1-MФ) or alternative-M2 (M2-MФ) activation. Until now there are no reports of the gonococcus effects on human MФ polarization. We assessed the phagocytic ability of monocyte-derived MФ (MDM) upon gonococcal infection by immunofluorescence and gentamicin protection experiments. Then, we evaluated cytokine profile and M1/M2 specific-surface markers on MФ challenged with N. gonorrhoeae and their proliferative effect on T cells. Our findings lead us to suggest N. gonorrhoeae stimulates a M2-MФ phenotype in which some of the M2b and none of the M1-MФ-associated markers are induced. Interestingly, N. gonorrhoeae exposure leads to upregulation of a Programmed Death Ligand 1 (PD-L1), widely known as an immunosuppressive molecule. Moreover, functional results showed that N. gonorrhoeae-treated MФ are unable to induce proliferation of human T-cells, suggesting a more likely regulatory phenotype. Taken together, our data show that N. gonorroheae interferes with MФ polarization. This study has important implications for understanding the mechanisms of clearance versus long-term persistence of N. gonorroheae infection and might be applicable for the development of new therapeutic strategies.

Alternatively activated microglia and macrophages in the central nervous system

Macrophages are important players in the fight against viral, bacterial, fungal and parasitic infections. From a resting state they may undertake two activation pathways, the classical known as M1, or the alternative known as M2. M1 markers are mostly mediators of pro-inflammatory responses whereas M2 markers emerge for resolution and cleanup. Microglia exerts in the central nervous system (CNS) a function similar to that of macrophages in the periphery. Microglia activation and proliferation occurs in almost any single pathology affecting the CNS. Often microglia activation has been considered detrimental and drugs able to stop microglia activation were considered for the treatment of a variety of diseases. Cumulative evidence shows that microglia may undergo the alternative activation pathway, express M2-type markers and contribute to neuroprotection. This review focuses on details about the role of M2 microglia and in the approaches available for its identification. Approaches to drive the M2 phenotype and data on its potential in CNS diseases are also reviewed.

Intercellular interplay between Sirt1 signalling and cell metabolism in immune cell biology

Sirtuins are evolutionarily conserved class III histone deacetylases that have been the focus of intense scrutiny and interest since the discovery of Sir2 as a yeast longevity factor. Early reports demonstrated an important role of Sirt1 in aging and metabolism, but its critical regulatory role in the immune system has only been unveiled in recent years. In this review we discuss the latest advances in understanding the regulatory role of Sirt1 in immune responses as well as how Sirt1 translates metabolic cues to immune signals, which would bring new insights into both pathogenesis and potential therapeutic strategies of a variety of immune-related diseases, such as cancer, microbial infection, autoimmune diseases and transplantation.

The G2019S LRRK2 mutation increases myeloid cell chemotactic responses and enhances LRRK2 binding to actin-regulatory proteins

The Leucine rich repeat kinase 2 (LRRK2) gene is genetically and biochemically linked to several diseases that involve innate immunity. LRRK2 protein is highly expressed in phagocytic cells of the innate immune system, most notably in myeloid cells capable of mounting potent pro-inflammatory responses. Knockdown of LRRK2 protein in these cells reduces pro-inflammatory responses. However, the effect of LRRK2 pathogenic mutations that cause Parkinson's disease on myeloid cell function is not clear but could provide insight into LRRK2-linked disease. Here, we find that rats expressing G2019S LRRK2 have exaggerated pro-inflammatory responses and subsequent neurodegeneration after lipopolysaccharide injections in the substantia nigra, with a marked increase in the recruitment of CD68 myeloid cells to the site of injection. While G2019S LRRK2 expression did not affect immunological homeostasis, myeloid cells expressing G2019S LRRK2 show enhanced chemotaxis both in vitro in two-chamber assays and in vivo in response to thioglycollate injections in the peritoneum. The G2019S mutation enhanced the association between LRRK2 and actin-regulatory proteins that control chemotaxis. The interaction between G2019S LRRK2 and actin-regulatory proteins can be blocked by LRRK2 kinase inhibitors, although we did not find evidence that LRRK2 phosphorylated these interacting proteins. These results suggest that the primary mechanism of G2019S LRRK2 with respect to myeloid cell function in disease may be related to exaggerated chemotactic responses.

Chronic rhinosinusitis and cystic fibrosis: the interaction between sinus bacteria and mucosal immunity

BACKGROUND

Chronic rhinosinusitis (CRS) is highly prevalent in cystic fibrosis (CF) patients, in whom a close correlation exists between the microbiology of the upper and lower respiratory tracts. We have reported intramucosal bacterial microcolonies in the sinus mucosa from idiopathic CRS patients and have made observations suggesting that these may result from mucosal immunotolerance secondary to altered macrophage function. In this study, we sought to determine whether intramucosal microcolonies exist in the mucosa of CF patients with CRS, and to investigate the associated mucosal immunology.

METHODS

Mucus swabs and tissue biopsies were taken from 9 patients with CF undergoing functional endoscopic sinus surgery (FESS) for CRS, 11 with idiopathic CRS undergoing FESS, and 9 with normal sinuses having transnasal pituitary surgery. Microbiology samples were taken for culture and intramucosal microcolonies were sought using Gram staining. Mucosal immune cells were identified using fluorescent immunohistochemistry.

RESULTS

Positive culture rates were similar between CRS patients and controls, but there were significantly more intramucosal microcolonies in the CRS groups (8/9 CF-CRS, 7/11 CRS), compared to controls (1/9). Furthermore, the biodensity of intramucosal microcolonies was significantly higher in CF-CRS than idiopathic CRS. Mirroring the microbiological observations, the number of CD163+ macrophages was significantly increased in CF-CRS compared to idiopathic CRS (p = 0.03).

CONCLUSION

Intramucosal bacteria exist within the sinus mucosa of patients with CF, and in significantly greater numbers than in idiopathic CRS patients. We speculate that intramucosal microcolonies may also exist in the lower respiratory tract mucosa in CF and play a role in disease recalcitrance.

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.

The chemokine CCL5 induces selective migration of bovine classical monocytes and drives their differentiation into LPS-hyporesponsive macrophages in vitro

Human and mouse studies indicate distinct roles of selected chemokines for monocyte subset attraction. We therefore analyzed the still unknown sensitivity and response of bovine monocyte subsets toward two monocyte-attracting chemokines (CCL2, CCL5). Only CCL5 induced a significant Ca(2+)influx and migration response in bovine monocytes, with classical and intermediate monocytes being significantly stimulated and attracted compared to nonclassical monocytes. The presence of CCL5 during in vitro macrophage differentiation did not alter their capacity to phagocytize or to generate reactive oxygen species upon stimulation with E. coli. However, macrophages differentiated in the presence of CCL5 displayed an altered phenotype with significantly less expressed CD14 and MHC class II molecules, whereas CD16 was upregulated. Moreover, CCL5-differentiated macrophages displayed a reduced upregulation of CXCL8, ARG1, IL6 and IL10 mRNA. Taken together, CCL5 but not CCL2 mainly attract bovine classical monocytes and promote their differentiation into LPS-hypo-responsive macrophages.

The role of macrophages in the innate immune response to Streptococcus pneumoniae and Staphylococcus aureus: mechanisms and contrasts

Macrophages are critical mediators of innate immune responses against bacteria. The Gram-positive bacteria Streptococcus pneumoniae and Staphylococcus aureus express a range of virulence factors, which challenge macrophages' immune competence. We review how macrophages respond to this challenge. Macrophages employ a range of strategies to phagocytose and kill each pathogen. When the macrophages capacity to clear bacteria is overwhelmed macrophages play important roles in orchestrating the inflammatory response through pattern recognition receptor-mediated responses. Macrophages also ensure the inflammatory response is tightly constrained, to avoid tissue damage, and play an important role in downregulating the inflammatory response once initial bacterial replication is controlled.

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.

Processing of CXCL12 impedes the recruitment of endothelial progenitor cells in diabetic wound healing

High blood sugar levels result in defective wound healing processes in diabetic patients. Endothelial progenitor cells (EPCs) play an important role in vasculogenesis, and thereby contribute to reconstitution of the microcirculation and healing. This study aimed to determine the possible mechanism by which the numbers of circulating EPCs are regulated in response to tissue wounding. In the streptozotocin-induced diabetic mouse model, we found that phagocytes activated by local inflammatory cytokines in the wound interfere with the mobilization and recruitment of EPCs to the lesion area. Specifically, the activated macrophages inactivate CXCL12, the major chemokine for EPC recruitment, via matrix metalloproteinases (MMPs), and thereby prevent local chemotaxis and subsequent homing of EPCs to the wound. The wound healing process is delayed by local administration of inflammatory cytokines, and its rate is increased by MMP inhibitors. This study indicates that local inhibition of MMPs is beneficial for regeneration of damaged vessels, and may explain poor wound healing in diabetic patients, thus demonstrating its potential utility as a local treatment therapy to promote diabetic wound healing.

The interaction between bacteria and mucosal immunity in chronic rhinosinusitis: a prospective cross-sectional analysis

BACKGROUND

We have detected intramucosal bacteria within the sinus mucosa of patients with chronic rhinosinusitis (CRS), but our attempts at characterizing these did not yield any discernible genotypic or phenotypic differences from surface bacteria. We hypothesized that the presence of intramucosal microcolonies reflected host mucosal immune dysfunction. This study characterizes the activation status of T cells, B cells, and macrophages in the sinus mucosa of patients with CRS and controls and determines the impact of bacteria on mucosal immunology.

METHODS

Swabs and mucosal biopsy specimens were taken from 27 patients with CRS undergoing sinus surgery and 9 patients with normal sinuses having transnasal pituitary surgery. Microcolonies were detected using Gram staining, and the immune cells were characterized by immunohistochemical techniques.

RESULTS

Swab culture rates for Staphylococcus aureus were similar between CRS and controls. However, there were significantly more intramucosal microcolonies in CRS (59% versus 11%) than in controls (p = 0.02). There were significantly more immune cells in CRS. Percentage of activated T and B cells were similar between CRS and controls, but there were significantly more CD163(+) M2 macrophages in patients with CRS (p = 0.0004). Furthermore, percentage of CD163(+) macrophages showed a positive correlation with disease severity. The presence of bacteria had no impact on immunology or disease severity.

CONCLUSION

Tolerance of intramucosal microcolonies in CRS may reflect altered macrophage function in the host mucosa. The clinical severity of CRS is also dependent on the host mucosa immune dysfunction, rather than the presence of intramucosal microcolonies.

Manipulation of the mononuclear phagocyte system by Mycobacterium tuberculosis

Over the past 20 years, there has been an emerging appreciation about the role of the mononuclear phagocyte system (MPS) to control and eradicate pathogens. Likewise, there have been significant advances in dissecting the mechanisms involved in the microbial subversion of MPS cells, mainly affecting their differentiation and effector functions. Mycobacterium tuberculosis is a chronic bacterial pathogen that represents an enigma to the field because of its remarkable ability to thrive in humans. One reason is that M. tuberculosis renders a defective MPS compartment, which is perhaps the most ingenious strategy for survival in the host given the prominence of these cells to modulate microenvironments, their function as sentinels and orchestrators of the immune response, and their pathogenic role as reservoirs for microbial persistence. In this article, the principal strategies used by M. tuberculosis to subvert the MPS compartment are presented along with emerging concepts.

Spleen-derived macrophages are readily polarized into classically activated (M1) or alternatively activated (M2) states

Bone marrow derived macrophages (BM-MΦ) that differentiate from precursor cells can be polarized into classically activated pro-inflammatory (M1) or alternatively activated (M2) states depending upon the cytokine microenvironment. We questioned whether tissue MΦ, such as spleen-derived MΦ (Sp-MΦ), have the ability to differentiate into M1 or M2 cells. We show in response to activation with IFN-gamma (IFN-γ) and lipopolysaccharide (LPS), that the Sp-MΦ readily acquired an M1 status indicated by up-regulation of iNOS mRNA, nitric oxide (NO) production, and the co-stimulatory molecule CD86. Conversely, Sp-MΦ exposed to IL-4 exhibited increased levels of mannose receptor (CD 206), arginase-1 (Arg)-1 mRNA expression, and significant urea production typical of M2 cells. At this stage of differentiation, the M2 Sp-MΦ were more efficient at phagocytosis of cell-associated antigens than their M1 counterparts. This polarization was not indefinite as the cells could revert back to their original state upon the removal of stimuli and exhibited flexibility to convert from M2 to M1. Remarkably, both M1 and M2 Sp-MΦ induced more CD4 expression on their cells surface after stimulation. We also demonstrate that adherent macrophages cultured for a short term in IL-4 enhances ARG-1 and YM-1 mRNA along with increasing urea producing capacity: traits indicative of an M2 phenotype. Moreover, in response to in vivo virus infection, the adherent macrophages obtained from spleens rapidly express iNOS. These results provide new evidence for the polarization capabilities of Sp-MΦ when exposed to pro-inflammatory or anti-inflammatory cytokines.

Proteomic characterization of human proinflammatory M1 and anti-inflammatory M2 macrophages and their response to Candida albicans

In response to different stimuli, macrophages can differentiate into either a pro-inflammatory subtype (M1, classically activated macrophages) or acquire an anti-inflammatory phenotype (M2, alternatively activated macrophages). Candida albicans is the most important opportunistic fungus in nosocomial infections, and it is contended by neutrophils and macrophages during the first steps of the invasive infection. Murine macrophages responses to C. albicans have been widely studied, whereas the responses of human-polarized macrophages remain less characterized. In this study, we have characterized the proteomic differences between human M1- and M2-polarized macrophages, both in basal conditions and in response to C. albicans, by quantitative proteomics (2DE). This proteomic approach allowed us to identify metabolic routes and cytoskeletal rearrangement components that are the most relevant differences between M1 and M2 macrophages. The analysis has revealed fructose-1,6-bisphosphatase 1, a critical enzyme in gluconeogenesis, up-regulated in M1, as a novel protein marker for macrophage polarization. Regarding the response to C. albicans, an M1-to-M2 switch in polarization was observed. This M1-to-M2 switch might contribute to Candida pathogenicity by decreasing the generation of specific immune responses, thus enhancing fungal survival and colonization, or instead, may be part of the host attempt to reduce the inflammation and limit the damage of the infection.

Tau-tubulin kinase

Tau-tubulin kinase (TTBK) belongs to casein kinase superfamily and phosphorylates microtubule-associated protein tau and tubulin. TTBK has two isoforms, TTBK1 and TTBK2, which contain highly homologous catalytic domains but their non-catalytic domains are distinctly different. TTBK1 is expressed specifically in the central nervous system and is involved in phosphorylation and aggregation of tau. TTBK2 is ubiquitously expressed in multiple tissues and genetically linked to spinocerebellar ataxia type 11. TTBK1 directly phosphorylates tau protein, especially at Ser422, and also activates cycline-dependent kinase 5 in a unique mechanism. TTBK1 protein expression is significantly elevated in Alzheimer’s disease (AD) brains, and genetic variations of the TTBK1 gene are associated with late-onset Alzheimer’s disease in two cohorts of Chinese and Spanish populations. TTBK1 transgenic mice harboring the entire 55-kilobase genomic sequence of human TTBK1 show progression of tau accumulation, neuroinflammation, and neurodegeneration when crossed with tau mutant mice. Our recent study shows that there is a striking switch in mononuclear phagocyte and activation phenotypes in the anterior horn of the spinal cord from alternatively activated (M2-skewed) microglia in P301L tau mutant mice to pro-inflammatory (M1-skewed) infiltrating peripheral monocytes by crossing the tau mice with TTBK1 transgenic mice. TTBK1 is responsible for mediating M1-activated microglia-induced neurotoxicity, and its overexpression induces axonal degeneration in vitro. These studies suggest that TTBK1 is an important molecule for the inflammatory axonal degeneration, which may be relevant to the pathobiology of tauopathy including AD.

Proresolving lipid mediators and mechanisms in the resolution of acute inflammation

Inflammatory responses, like all biological cascades, are shaped by a delicate balance between positive and negative feedback loops. It is now clear that in addition to positive and negative checkpoints, the inflammatory cascade rather unexpectedly boasts an additional checkpoint, a family of chemicals that actively promote resolution and tissue repair without compromising host defense. Indeed, the resolution phase of inflammation is just as actively orchestrated and carefully choreographed as its induction and inhibition. In this review, we explore the immunological consequences of omega-3-derived specialized proresolving mediators (SPMs) and discuss their place within what is currently understood of the role of the arachidonic acid-derived prostaglandins, lipoxins, and their natural C15-epimers. We propose that treatment of inflammation should not be restricted to the use of inhibitors of the acute cascade (antagonism) but broadened to take account of the enormous therapeutic potential of inducers (agonists) of the resolution phase of inflammation.

Escherichia coli and Candida albicans induced macrophage extracellular trap-like structures with limited microbicidal activity

The formation of extracellular traps (ETs) has recently been recognized as a novel defense mechanism in several types of innate immune cells. It has been suggested that these structures are toxic to microbes and contribute significantly to killing several pathogens. However, the role of ETs formed by macrophages (METs) in defense against microbes remains little known. In this study, we demonstrated that a subset of murine J774A.1 macrophage cell line (8% to 17%) and peritoneal macrophages (8.5% to 15%) form METs-like structures (METs-LS) in response to Escherichia coli and Candida albicans challenge. We found only a portion of murine METs-LS, which are released by dying macrophages, showed detectable killing effects on trapped E. coli but not C. albicans. Fluorescence and scanning electron microscopy analyses revealed that, in vitro, both microorganisms were entrapped in J774A.1 METs-LS composed of DNA and microbicidal proteins such as histone, myeloperoxidase and lysozyme. DNA components of both nucleus and mitochondrion origins were detectable in these structures. Additionally, METs-LS formation occurred independently of ROS produced by NADPH oxidase, and this process did not result in cell lysis. In summary, our results emphasized that microbes induced METs-LS in murine macrophage cells and that the microbicidal activity of these METs-LS differs greatly. We propose the function of METs-LS is to contain invading microbes at the infection site, thereby preventing the systemic diffusion of them, rather than significantly killing them.

Tropheryma whipplei, the agent of Whipple's disease, affects the early to late phagosome transition and survives in a Rab5- and Rab7-positive compartment

Tropheryma whipplei, the agent of Whipple's disease, inhibits phago-lysosome biogenesis to create a suitable niche for its survival and replication in macrophages. To understand the mechanism by which it subverts phagosome maturation, we used biochemical and cell biological approaches to purify and characterise the intracellular compartment where Tropheryma whipplei resides using mouse bone-marrow-derived macrophages. We showed that in addition to Lamp-1, the Tropheryma whipplei phagosome is positive for Rab5 and Rab7, two GTPases required for the early to late phagosome transition. Unlike other pathogens, inhibition of PI(3)P production was not the mechanism for Rab5 stabilisation at the phagosome. Overexpression of the inactive, GDP-bound form of Rab5 bypassed the pathogen-induced blockade of phago-lysosome biogenesis. This suggests that Tropheryma whipplei blocks the switch from Rab5 to Rab7 by acting on the Rab5 GTPase cycle. A bio-informatic analysis of the Tropheryma whipplei genome revealed a glyceraldehyde-3-phosphate dehydrogenase (GAPDH) homologous with the GAPDH of Listeria monocytogenes, and this may be the bacterial protein responsible for blocking Rab5 activity. To our knowledge, Tropheryma whipplei is the first pathogen described to induce a “chimeric” phagosome stably expressing both Rab5 and Rab7, suggesting a novel and specific mechanism for subverting phagosome maturation.

Hiding in Plain Sight: Interplay between Staphylococcal Biofilms and Host Immunity

Staphylococcus aureus and Staphylococcus epidermidis are notable for their propensity to form biofilms on implanted medical devices. Staphylococcal biofilm infections are typified by their recalcitrance to antibiotics and ability to circumvent host immune-mediated clearance, resulting in the establishment of chronic infections that are often recurrent in nature. Indeed, the immunomodulatory lifestyle of biofilms seemingly shapes the host immune response to ensure biofilm engraftment and persistence in an immune competent host. Here, we provide a brief review of the mechanisms whereby S. aureus and S. epidermidis biofilms manipulate host–pathogen interactions and discuss the concept of microenvironment maintenance in infectious outcomes, as well as speculate how these findings pertain to the challenges of staphylococcal vaccine development.

The regulatory peptide pidotimod facilitates M2 macrophage polarization and its function

Pidotimod is a synthetic dipeptide with biological and immunological activity in innate immune responses. It has been reported that pidotimod could promote functional maturation of dendritic cells, but little is known about the regulation of macrophages. Recent studies have demonstrated that M1 or M2 polarized macrophages are of great importance for responses to microorganism infection or host mediators. The aim of this study was to determine the effectiveness of pidotimod on mouse bone marrow-derived macrophage polarization and its function. The results showed that pidotimod had no influence on M1-polarized macrophage. While interestingly, a significant increase of M2 marker gene expression (Arg1, Fizz1, Ym1, MR) was observed (p < 0.01) in IL-4-induced M2 macrophage treated with pidotimod. In addition, cell surface expression of mannose receptor was dramatically enhanced using fluorescence activated cell sorter (FACS) analysis. Furthermore, the function of M2 macrophage was also determinated. The results showed that the supernatant of pidotimod-treated M2 macrophage could increase the migration (p < 0.05) and enhance the wound closure rate (p < 0.05) of MLE-12 cells. Collectively, it could be concluded that pidotimod significantly facilitated IL-4-induced M2 macrophage polarization and improves its function.

Maleylated-BSA suppresses lipopolysaccharide-induced IL-6 production by activating the ERK-signaling pathway in murine RAW264.7 cells

Macrophages are well known for their ability to induce diverse beneficial immune responses, especially in the defense against pathogens. However, an excessive activation of macrophages may cause harmful inflammation. In this context, the suppression of excessive macrophage activation would be a promising therapeutic strategy for treating inflammatory diseases. We have previously found that maleylated-bovine serum albumin (maleylated-BSA) suppresses the production of inflammatory mediators in murine macrophages. However, the immunosuppressive effects and underlying mechanism(s) of maleylated-BSA remain unclear. Here, we report that pretreatment with maleylated-BSA strongly inhibited the production of interleukin 6 (IL-6) induced by bacterial lipopolysaccharide (LPS) in murine RAW264.7 cells. This inhibitory effect of maleylated-BSA on LPS-induced IL-6 production was eliminated by treatment with an extracellular signal-regulated kinase (ERK) inhibitor, U0126, indicating the involvement of ERK pathways. Taken together, we have shown that maleylated-BSA suppresses LPS-induced production of IL-6 via the activation of an ERK signaling pathway in murine macrophages. The findings of this study imply the possibility of a novel therapeutic strategy for inflammatory diseases.

Pathways mediating resolution of inflammation: when enough is too much

Patients with critical illness, and in particular sepsis, are now recognized to undergo unifying, pathogenic disturbances of immune function. Whilst scientific and therapeutic focus has traditionally been on understanding and modulating the initial pro-inflammatory limb, recent years have witnessed a refocusing on the development and importance of immunosuppressive 'anti-inflammatory' pathways. Several mechanisms are known to drive this phenomenon; however, no overriding conceptual framework justifies them. In this article we review the contribution of pro-resolution pathways to this phenotype, describing the observed immune alterations in terms of either a failure of resolution of inflammation or the persistence of pro-resolution processes causing inappropriate 'injurious resolution'-a novel hypothesis. The dysregulation of key processes in critical illness, including apoptosis of infiltrating neutrophils and their efferocytosis by macrophages, are discussed, along with the emerging role of specialized cell subtypes Gr1(+) CD11b(+) myeloid-derived suppressor cells and CD4(+) CD25(+) FoxP3(+) T-regulatory cells.

5-Lipoxygenase contributes to PPARγ activation in macrophages in response to apoptotic cells

Macrophage polarization to an anti-inflammatory phenotype upon contact with apoptotic cells is a contributing hallmark to immune suppression during the late phase of sepsis. Although the peroxisome proliferator-activated receptor γ (PPARγ) supports this macrophage phenotype switch, it remains elusive how apoptotic cells activate PPARγ. Assuming that a molecule causing PPARγ activation in macrophages originates in the cell membrane of apoptotic cells we analyzed lipid rafts from apoptotic, necrotic, and living human Jurkat T cells which showed the presence of 5-lipoxygenase (5-LO) in lipid rafts of apoptotic cells only. Incubating macrophages with lipid rafts of apoptotic, but not necrotic or living cells, induced PPAR responsive element (PPRE)-driven mRuby reporter gene expression in RAW 264.7 macrophages stably transduced with a 4xPPRE containing vector. Experiments with lipid rafts of apoptotic murine EL4 T cells revealed similar results. To verify the involvement of 5-LO in activating PPARγ in macrophages, Jurkat T cells were incubated with the 5-LO inhibitor MK-866 prior to induction of apoptosis, which failed to induce mRuby expression. Similar results were obtained with lipid rafts of apoptotic EL4 T cells preexposed to the 5-LO inhibitors zileuton and CJ-13610. Interestingly, Jurkat T cells overexpressing 5-LO failed to activate PPARγ in macrophages, while their 5-LO overexpressing apoptotic counterparts did. Our results suggest that during apoptosis 5-LO gets associated with lipid rafts and synthesizes ligands that in turn stimulate PPARγ in macrophages.

Impact of azithromycin treatment on macrophage gene expression in subjects with cystic fibrosis

BACKGROUND

Azithromycin treatment improves clinical parameters in patients with CF, and alters macrophage activation from a pro-inflammatory (M1) phenotype to a pro-fibrotic, alternatively activated (M2) phenotype. The transcriptional profile of cells from patients receiving azithromycin is unknown.

METHODS

Gene expression in association with macrophage polarization, inflammation, and tissue remodeling was assessed from sputum samples collected from patients with CF. Transcriptional profiles and clinical characteristics, including azithromycin therapy, were compared.

RESULTS

Expression of NOS2 and TNFα was decreased in subjects receiving azithromycin, whereas expression of M2-associated genes was unaffected. Principal component analysis revealed gene expression profiles consistent with M1- (MMP9, NOS2, and TLR4) or M2-polarization (CCL18, fibronectin, and MR1) in select subject groups. These expression signatures did not significantly correlate with clinical characteristics.

CONCLUSIONS

Pro-inflammatory gene expression was low in subjects receiving AZM. Genes were stratified into groupings characteristic of M1- or M2-polarization, suggesting that overall polarization status is distinct among patient groups.

Chronic pulmonary cavitary tuberculosis in rabbits: a failed host immune response

The molecular determinants of the immune response to Mycobacterium tuberculosis HN878 infection in a rabbit model of pulmonary cavitary tuberculosis were studied. Aerosol infection of rabbits resulted in a highly differentially expressed global transcriptome in the lungs at 2 weeks, which dropped at 4 weeks and then gradually increased. While IFNγ was progressively upregulated throughout the infection, several other genes in the IFNγ network were not. T-cell activation network genes were gradually upregulated and maximally induced at 12 weeks. Similarly, the IL4 and B-cell activation networks were progressively upregulated, many reaching high levels between 12 and 16 weeks. Delayed peak expression of genes associated with macrophage activation and Th1 type immunity was noted. Although spleen CD4(+) and CD8(+) T cells showed maximal tuberculosis antigen-specific activation by 8 weeks, macrophage activation in lungs, lymph nodes and spleen did not peak until 12 weeks. In the lungs, infecting bacilli grew exponentially up to 4 weeks, followed by a steady-state high bacillary load to 12 weeks that moderately increased during cavitation at 16 weeks. Thus, the outcome of HN878 infection of rabbits was determined early during infection by a suboptimal activation of innate immunity and delayed T-cell activation.

Evaluation of arginine metabolism for the analysis of M1/M2 macrophage activation in human clinical specimens

BACKGROUND

Macrophage heterogeneity reflects their plasticity in response to environmental stimuli. Usually human macrophages are characterized by analysis of surface molecules or cytokine expression while functional assays are established in the mouse system but lacking for various human specimens.

METHODS

To evaluate the value of analysis of arginine metabolism for characterization of human macrophage differentiation, we analyzed nitrite production and arginase activity in plasma, duodenal biopsies, and in vitro differentiated macrophages of patients with classical Whipple's disease.

RESULTS

We demonstrate that it is feasible to determine the content of urea in supernatants of stimulated duodenal biopsies, arginase activity in fresh duodenal biopsies and plasma samples, and arginase activity and nitrite production in lysates and supernatants of in vitro differentiated macrophages. However, only selected tests are appropriate to define macrophage polarization in human specimens.

CONCLUSION

Analysis of arginine metabolism is not suitable for the characterization of in vitro differentiated human macrophages. Besides the measurement of nitrite in duodenal biopsy supernatants, the determination of arginase activity in human plasma seems to be a reasonable functional test to detect enhanced M2 macrophage activation and, thus, is of great value for the analysis of macrophage activity with a minimum of material and costs.

Periodontal disease immunology: 'double indemnity' in protecting the host

During the last two to three decades our understanding of the immunobiology of periodontal disease has increased exponentially, both with respect to the microbial agents triggering the disease process and the molecular mechanisms of the host engagement maintaining homeostasis or leading to collateral tissue damage. These foundational scientific findings have laid the groundwork for translating cell phenotype, receptor engagement, intracellular signaling pathways and effector functions into a 'picture' of the periodontium as the host responds to the 'danger signals' of the microbial ecology to maintain homeostasis or succumb to a disease process. These findings implicate the chronicity of the local response in attempting to manage the microbial challenge, creating a 'Double Indemnity' in some patients that does not 'insure' health for the periodontium. As importantly, in reflecting the title of this volume of Periodontology 2000, this review attempts to inform the community of how the science of periodontal immunology gestated, how continual probing of the biology of the disease has led to an evolution in our knowledge base and how more recent studies in the postgenomic era are revolutionizing our understanding of disease initiation, progression and resolution. Thus, there has been substantial progress in our understanding of the molecular mechanisms of host-bacteria interactions that result in the clinical presentation and outcomes of destructive periodontitis. The science has embarked from observations of variations in responses related to disease expression with a focus for utilization of the responses in diagnosis and therapeutic outcomes, to current investigations using cutting-edge fundamental biological processes to attempt to model the initiation and progression of soft- and hard-tissue destruction of the periodontium. As importantly, the next era in the immunobiology of periodontal disease will need to engage more sophisticated experimental designs for clinical studies to enable robust translation of basic biologic processes that are in action early in the transition from health to disease, those which stimulate microenvironmental changes that select for a more pathogenic microbial ecology and those that represent a rebalancing of the complex host responses and a resolution of inflammatory tissue destruction.

Macrophages are unsuccessful in clearing aggregated alpha-synuclein from the gastrointestinal tract of healthy aged Fischer 344 rats

With age, alpha-synuclein (α-SYNC) misfolds and forms insoluble deposits of protein in the myenteric plexus, leading presumably to dystrophy and degeneration in the circuitry controlling gastrointestinal (GI) function. The present experiment examined aggregates of α-SYNC in the aging small intestine and investigated how macrophages in the wall of the GI tract respond to these aberrant deposits. Groups of adult and aged Fisher 344 rats were studied. Whole mounts of duodenal, jejunal, and ileal smooth muscle wall, including the myenteric plexus, were prepared. Double labeling immunohistochemistry was used to stain α-SYNC protein and the phenotypic macrophage antigens CD163 and MHCII. Alpha-synuclein accumulated in dense aggregates in axons of both postganglionic and preganglionic neurons throughout the small intestine. Staining patterns suggested that deposits of protein occur initially in axonal terminals and then spread retrogradely toward the somata. Macrophages that were adjacent to dystrophic terminal processes were swollen and contained vacuoles filled with insoluble α-SYNC, and these macrophages commonly had the phenotype of alternatively activated phagocytes. The present results suggest that macrophages play an active phagocytotic role in removing α-SYNC aggregates that accumulate with age in the neural circuitry of the gut. Our observations further indicate that this housekeeping response does not clear the protein sufficiently to eliminate all synucleinopathies or their precursor aggregates from the healthy aging GI tract. Thus, accumulating deposits of insoluble α-SYNC in the wall of the GI tract may contribute, especially when compounded by disease or inflammation, to the age-associated neuropathies in the gut that compromise GI function.

Induction of CCL8/MCP-2 by mycobacteria through the activation of TLR2/PI3K/Akt signaling pathway

Pleural tuberculosis (TB), together with lymphatic TB, constitutes more than half of all extrapulmonary cases. Pleural effusions (PEs) in TB are representative of lymphocytic PEs which are dominated by T cells. However, the mechanism underlying T lymphocytes homing and accumulation in PEs is still incompletely understood. Here we performed a comparative analysis of cytokine abundance in PEs from TB patients and non-TB patients by protein array analysis and observed that MCP-2/CCL8 is highly expressed in the TB-PEs as compared to peripheral blood. Meanwhile, we observed that CCR5, the primary receptor used by MCP-2/CCL8, is mostly expressed on pleural CD4⁺ T lymphocytes. Furthermore, we found that infection with either Mycobacterium bovis Bacillus Calmette-Guérin (BCG) or Mycobacterium tuberculosis H37Rv induced production of MCP-2/CCL8 at both transcriptional and protein level in Raw264.7 and THP-1 macrophage cells, mouse peritoneal macrophages as well as human PBMC monocyte-derived macrophages (MDMs). The induction of MCP-2/CCL8 by mycobacteria is dependent on the activation of TLR2/PI3K/Akt and p38 signaling pathway. We conclude that accumulation of MCP-2/CCL8 in TB-PEs may function as a biomarker for TB diagnosis.

Isolation, culture, and functional evaluation of bone marrow-derived macrophages

Macrophages are cellular components of the immune system that are essential for responding to pathogens, initiating inflammation, and maintaining tissue homeostasis. Isolation, culture, and functional characterization of bone marrow-derived macrophages from mice are exceptionally powerful techniques used to examine aspects of macrophage biology in vitro. These cells can be used to study effector functions, such as phagocytosis, cytokine secretion, oxidative burst, migration, antigen processing and presentation, in the context of wild-type, gene-ablated, and/or transgenic mice. The quantity, purity, and ease of culture of these cells enhance their utility for primary cell cultures. This chapter outlines protocols used to generate, quantitate, and functionally evaluate macrophages derived from bone marrow precursor cells.

Haemophilus ducreyi-induced interleukin-10 promotes a mixed M1 and M2 activation program in human macrophages

During microbial infection, macrophages are polarized to classically activated (M1) or alternatively activated (M2) cells in response to microbial components and host immune mediators. Proper polarization of macrophages is critical for bacterial clearance. To study the role of macrophage polarization during Haemophilus ducreyi infection, we analyzed a panel of macrophage surface markers in skin biopsy specimens of pustules obtained from experimentally infected volunteers. Lesional macrophages expressed markers characteristic of both M1 and M2 polarization. Monocyte-derived macrophages (MDM) also expressed a mixed M1 and M2 profile of surface markers and cytokines/chemokines upon infection with H. ducreyi in vitro. Endogenous interleukin 10 (IL-10) produced by infected MDM downregulated and enhanced expression of several M1 and M2 markers, respectively. Bacterial uptake, mediated mainly by class A scavenger receptors, and activation of mitogen-activated protein kinase and phosphoinositide 3-kinase signaling pathways were required for H. ducreyi-induced IL-10 production in MDM. Compared to M1 cells, IL-10-polarized M2 cells displayed enhanced phagocytic activity against H. ducreyi and similar bacterial killing. Thus, IL-10-modulated macrophage polarization may contribute to H. ducreyi clearance during human infection.

Blood leukocytes and macrophages of various phenotypes have distinct abilities to form podosomes and to migrate in 3D environments

Leukocytes migrate through most tissues in the body, a process which takes place in 3D environments. We have previously shown that macrophages use the amoeboid migration mode in porous matrices such as fibrillar collagen I and the mesenchymal mode involving podosomes and matrix proteolysis in dense matrices such as Matrigel. Whether such a plasticity may apply to other leukocytes and to all subsets of macrophages is unknown. Here, we therefore provide a comparative analysis of the in vitro 3D migration modes adopted by primary human leukocytes. Blood-derived monocytes, neutrophils and T lymphocytes were found to use the amoeboid mode in a porous fibrillar collagen I matrix but were unable to infiltrate dense Matrigel and to form podosomes. M2-polarized macrophages and elicited peritoneal macrophages formed podosome rosettes, degraded the ECM and infiltrated both matrices. In contrast, M1 macrophages were motionless in 2D and 3D environments, whilst resident macrophages, devoid of podosomes, were only able to use the amoeboid mode. Thus, we conclude that whereas all leukocytes use the amoeboid mode to migrate through porous matrices, it is only certain macrophages that can adopt the mesenchymal mode that permits migration through dense matrices. Interestingly, the acquisition of mesenchymal migration capacity by macrophages correlates with the presence of podosomes and with their capacity to organize those as rosettes, which appears to be modulated by their differentiation and polarization states. As a perspective, specific control of the mesenchymal migration would be a potential target for therapeutic approaches aiming at decreasing macrophage tissue infiltration.

Whole-cell MALDI-TOF MS: a new tool to assess the multifaceted activation of macrophages

Whole-cell MALDI-TOF MS is routinely used to identify bacterial species in clinical samples. This technique has also proven to allow identification of intact mammalian cells, including macrophages. Here, we wondered whether this approach enabled the assessment human macrophages plasticity. The whole-cell MALDI-TOF spectra of macrophages stimulated with IFN-γ and IL-4, two inducers of M1 and M2 macrophage polarisation, consisted of peaks ranging from 2 to 12 kDa. The spectra of unstimulated and stimulated macrophages were clearly different. The fingerprints induced by the M1 agonists, IFN-γ, TNF, LPS and LPS+IFN-γ, and the M2 agonists, IL-4, TGF-β1 and IL-10, were specific and readily identifiable. Thus, whole-cell MALDI-TOF MS was able to characterise M1 and M2 macrophage subtypes. In addition, the fingerprints induced by extracellular (group B Streptococcus, Staphylococcus aureus) or intracellular (BCG, Orientia tsutsugamushi, Coxiella burnetii) bacteria were bacterium-specific. The whole-cell MALDI-TOF MS fingerprints therefore revealed the multifaceted activation of human macrophages. This approach opened a new avenue of studies to assess the immune response in the clinical setting, by monitoring the various activation patterns of immune cells in pathological conditions.

Acute injury in the peripheral nervous system triggers an alternative macrophage response

BACKGROUND

The activation of the immune system in neurodegeneration has detrimental as well as beneficial effects. Which aspects of this immune response aggravate the neurodegenerative breakdown and which stimulate regeneration remains an open question. To unravel the neuroprotective aspects of the immune system we focused on a model of acute peripheral nerve injury, in which the immune system was shown to be protective.

METHODS

To determine the type of immune response triggered after axotomy of the sciatic nerve, a model for Wallerian degeneration in the peripheral nervous system, we evaluated markers representing the two extremes of a type I and type II immune response (classical vs. alternative) using real-time quantitative polymerase chain reaction (RT-qPCR), western blot, and immunohistochemistry.

RESULTS

Our results showed that acute peripheral nerve injury triggers an anti-inflammatory and immunosuppressive response, rather than a pro-inflammatory response. This was reflected by the complete absence of classical macrophage markers (iNOS, IFN γ, and IL12p40), and the strong up-regulation of tissue repair markers (arginase-1, Ym1, and Trem2). The signal favoring the alternative macrophage environment was induced immediately after nerve damage and appeared to be established within the nerve, well before the infiltration of macrophages. In addition, negative regulators of the innate immune response, as well as the anti-inflammatory cytokine IL-10 were induced. The strict regulation of the immune system dampens the potential tissue damaging effects of an over-activated response.

CONCLUSIONS

We here demonstrate that acute peripheral nerve injury triggers an inherent protective environment by inducing the M2 phenotype of macrophages and the expression of arginase-1. We believe that the M2 phenotype, associated with a sterile inflammatory response and tissue repair, might explain their neuroprotective capacity. As such, shifting the neurodegeneration-induced immune responses towards an M2/Th2 response could be an important therapeutic strategy.