Ly6Chi Monocyte Recruitment Is Responsible for Th2 Associated Host-Protective Macrophage Accumulation in Liver Inflammation due to Schistosomiasis

Accumulation of M2 macrophages in the liver, within the context of a strong Th2 response, is a hallmark of infection with the parasitic helminth, Schistosoma mansoni, but the origin of these cells is unclear. To explore this, we examined the relatedness of macrophages to monocytes in this setting. Our data show that both monocyte-derived and resident macrophages are engaged in the response to infection. Infection caused CCR2-dependent increases in numbers of Ly6C^hi monocytes in blood and liver and of CX₃CR1⁺ macrophages in diseased liver. Ly6C^hi monocytes recovered from liver had the potential to differentiate into macrophages when cultured with M-CSF. Using pulse chase BrdU labeling, we found that most hepatic macrophages in infected mice arose from monocytes. Consistent with this, deletion of monocytes led to the loss of a subpopulation of hepatic CD11c^hi macrophages that was present in infected but not naïve mice. This was accompanied by a reduction in the size of egg-associated granulomas and significantly exacerbated disease. In addition to the involvement of monocytes and monocyte-derived macrophages in hepatic inflammation due to infection, we observed increased incorporation of BrdU and expression of Ki67 and MHC II in resident macrophages, indicating that these cells are participating in the response. Expression of both M2 and M1 marker genes was increased in liver from infected vs. naive mice. The M2 fingerprint in the liver was not accounted for by a single cell type, but rather reflected expression of M2 genes by various cells including macrophages, neutrophils, eosinophils and monocytes. Our data point to monocyte recruitment as the dominant process for increasing macrophage cell numbers in the liver during schistosomiasis.     

M2 Polarization of Monocytes-Macrophages Is a Hallmark of Indian Post Kala-Azar Dermal Leishmaniasis

The high level of functional diversity and plasticity in monocytes/macrophages has been defined within in vitro systems as M1 (classically activated), M2 (alternatively activated) and deactivated macrophages, of which the latter two subtypes are associated with suppression of cell mediated immunity, that confers susceptibility to intracellular infection. Although the Leishmania parasite modulates macrophage functions to ensure its survival, what remains an unanswered yet pertinent question is whether these macrophages are deactivated or alternatively activated. This study aimed to characterize the functional plasticity and polarization of monocytes/macrophages and delineate their importance in the immunopathogenesis of Post kala-azar dermal leishmaniasis (PKDL), a chronic dermatosis of human leishmaniasis. Monocytes from PKDL patients showed a decreased expression of TLR-2/4, along with an attenuated generation of reactive oxidative/nitrosative species. At disease presentation, an increased mRNA expression of classical M2 markers CD206, ARG1 and PPARG in monocytes and lesional macrophages indicated M2 polarization of macrophages which was corroborated by increased expression of CD206 and arginase-1. Furthermore, altered vitamin D signaling was a key feature in PKDL, as disease presentation was associated with raised plasma levels of monohydroxylated vitamin D₃ and vitamin D3- associated genes, features of M2 polarization. Taken together, in PKDL, monocyte/macrophage subsets appear to be alternatively activated, a phenotype that might sustain disease chronicity. Importantly, repolarization of these monocytes to M1 by antileishmanial drugs suggests that switching from M2 to M1 phenotype might represent a therapeutic opportunity, worthy of future pharmacological consideration.     

IL-4Rα-Dependent Alternative Activation of Macrophages Is Not Decisive for Mycobacterium tuberculosis Pathology and Bacterial Burden in Mice

Classical activation of macrophages (caMph or M1) is crucial for host protection against Mycobacterium tuberculosis (Mtb) infection. Evidence suggests that IL-4/IL-13 alternatively activated macrophages (aaMph or M2) are exploited by Mtb to divert microbicidal functions of caMph. To define the functions of M2 macrophages during tuberculosis (TB), we infected mice deficient for IL-4 receptor α on macrophages (LysM^creIL-4Rα^-/lox) with Mtb. We show that absence of IL-4Rα on macrophages does not play a major role during infection with Mtb H37Rv, or the clinical Beijing strain HN878. This was demonstrated by similar mortality, bacterial burden, histopathology and T cell proliferation between infected wild-type (WT) and LysM^creIL-4Rα^-/lox mice. Interestingly, we observed no differences in the lung expression of inducible nitric oxide synthase (iNOS) and Arginase 1 (Arg1), well-established markers for M1/M2 macrophages among the Mtb-infected groups. Kinetic expression studies of IL-4/IL-13 activated bone marrow-derived macrophages (BMDM) infected with HN878, followed by gene set enrichment analysis, revealed that the MyD88 and IL-6, IL-10, G-CSF pathways are significantly enriched, but not the IL-4Rα driven pathway. Together, these results suggest that IL-4Rα-macrophages do not play a central role in TB disease progression.     

Probiotic Bacillus amyloliquefaciens mediate M1 macrophage polarization in mouse bone marrow-derived macrophages

Depending on the microenvironment, macrophages can acquire distinct functional phenotypes, referred to as classically activated M1 and M2. M1 macrophages are considered potent effector cells that kill intracellular pathogens, and M2 macrophages promote the resolution of wound healing. In this study, we are interested to know whether probiotic Bacillus amyloliquefaciens (Ba) can induce macrophages polarization. Real-time fluorescence PCR analysis demonstrated that the expression of IL-1β, iNOS, TNF-α and IL-6 genes for M1 macrophages was significantly increased at 1.5 h after probiotic Ba treatment compared to the probiotic Ba-free treatment (P < 0.01), whereas the expression of M2 macrophage marker genes (Arg1, Fizz1, MR, Ym1) was decreased (P < 0.05). Furthermore, the phagocytic activity was dramatically increased in the Ba-treated BMDMs using a FITC-dextran endocytosis assay. Together, these findings indicated that probiotic Ba facilitated polarization of M1 macrophages and enhanced its phagocytic capacity. The results expanded our knowledge about probiotic function-involved macrophage polarization.     

M2 Macrophages Activate WNT Signaling Pathway in Epithelial Cells: Relevance in Ulcerative Colitis

Macrophages, which exhibit great plasticity, are important components of the inflamed tissue and constitute an essential element of regenerative responses. Epithelial Wnt signalling is involved in mechanisms of proliferation and differentiation and expression of Wnt ligands by macrophages has been reported. We aim to determine whether the macrophage phenotype determines the expression of Wnt ligands, the influence of the macrophage phenotype in epithelial activation of Wnt signalling and the relevance of this pathway in ulcerative colitis. Human monocyte-derived macrophages and U937-derived macrophages were polarized towards M1 or M2 phenotypes and the expression of Wnt1 and Wnt3a was analyzed by qPCR. The effects of macrophages and the role of Wnt1 were analyzed on the expression of β-catenin, Tcf-4, c-Myc and markers of cell differentiation in a co-culture system with Caco-2 cells. Immunohistochemical staining of CD68, CD206, CD86, Wnt1, β-catenin and c-Myc were evaluated in the damaged and non-damaged mucosa of patients with UC. We also determined the mRNA expression of Lgr5 and c-Myc by qPCR and protein levels of β-catenin by western blot. Results show that M2, and no M1, activated the Wnt signaling pathway in co-culture epithelial cells through Wnt1 which impaired enterocyte differentiation. A significant increase in the number of CD206+ macrophages was observed in the damaged mucosa of chronic vs newly diagnosed patients. CD206 immunostaining co-localized with Wnt1 in the mucosa and these cells were associated with activation of canonical Wnt signalling pathway in epithelial cells and diminution of alkaline phosphatase activity. Our results show that M2 macrophages, and not M1, activate Wnt signalling pathways and decrease enterocyte differentiation in co-cultured epithelial cells. In the mucosa of UC patients, M2 macrophages increase with chronicity and are associated with activation of epithelial Wnt signalling and diminution in enterocyte differentiation.     

ADAMDEC1 promotes skin inflammation in rosacea via modulating the polarization of M1 macrophages

Rosacea is a chronic inflammatory cutaneous disease which mainly affects central face, leading to cosmetic disfigurement and compromised social psychology in billions of rosacea patients. Though the exact etiology of rosacea remains elusive, accumulating evidence has highlighted the dysfunction of innate immunity and inflammation in rosacea pathogenesis. Disintegrin Metalloprotease ADAM-like Decysin-1 (ADAMDEC1) is an orphan ADAM-like metalloprotease which is believed to be closely related to inflammation. Here for the first time, we reported that Adamdec1 expression was significantly increased in the skin lesions of rosacea patients and LL37–induced rosacea-like mouse models. Immunofluorescence analysis revealed co-localization of ADAMDEC1 and macrophages in patient and mouse biopsies. In cellular experiment, the expression of ADAMDEC1 was prominently elevated in M1 but not M2 macrophages. Knocking down of ADAMDEC1 significantly blunted M1 polarization in macrophages induced from human monocytes and THP-1 cell lines. Furthermore, silencing of Adamdec1 in LL-37-induced mouse model also suppressed the expression of M1 signature genes such as IL-6, iNOS and TNF-α, resulting in attenuated rosacea-like phenotype and inflammation. Taken together, our results demonstrate that ADAMDEC1 plays a pro-inflammatory role in rosacea via modulating the M1 polarization of macrophages.     

Intracellular Survival and Persistence of Chlamydia muridarum Is Determined by Macrophage Polarization

Macrophages can display a number of distinct phenotypes, known collectively as polarized macrophages. The best defined of these phenotypes are the classically-activated, interferon gamma (IFNγ)/LPS induced (M1) and alternatively-activated, IL-4 induced (M2) macrophages. The goal of this study is to characterize macrophage- Chlamydia interactions in the context of macrophage polarization. Here we use Chlamydia muridarum and murine bone-marrow derived macrophages to show Chlamydia does not induce M2 polarization in macrophages as a survival strategy. Unexpectedly, the infection of macrophages was silent with no upregulation of M1 macrophage-associated genes. We further demonstrate that macrophages polarized prior to infection have a differential capacity to control Chlamydia . M1 macrophages harbor up to 40-fold lower inclusion forming units (IFU) than non-polarized or M2 polarized macrophages. Gene expression analysis showed an increase in 16sRNA in M2 macrophages with no change in M1 macrophages. Suppressed Chlamydia growth in M1 macrophages correlated with the induction of a bacterial gene expression profile typical of persistence as evident by increased Euo expression and decreased Omp1 and Tal expression. Observations of permissive Chlamydia growth in non-polarized and M2 macrophages and persistence in M1 macrophages were supported through electron microscopy. This work supports the importance of IFNγ in the innate immune response to Chlamydia . However, demonstration that the M1 macrophages, despite an antimicrobial signature, fail to eliminate intracellular Chlamydia supports the notion that host–pathogen co-evolution has yielded a pathogen that can evade cellular defenses against this pathogen, and persist for prolonged periods of time in the host.     

β-Carotene exerts anti-colon cancer effects by regulating M2 macrophages and activated fibroblasts

The tumor microenvironment (TME), consisting of stromal fibroblasts, immune cells, cancer cells and other cell types, plays a crucial role in cancer progression and metastasis. M2 macrophages and activated fibroblasts (AFs) modulate behavior of cancer cells in the TME. Since nutritional effects on cancer progression, including colorectal cancer (CRC), may be mediated by alterations in the TME, we determined the ability of β-carotene (BC) to mediate anti-cancer effects through regulation of macrophage polarization and fibroblast activation in CRC. The M2 macrophage phenotype was induced by treating U937 cells with phorbol-12-myristate-13-acetate and interleukin (IL)-4. Treatment of these M2 macrophages with BC led to suppression of M2-type macrophage-associated markers and of the IL-6/STAT3 signaling pathway. In separate experiments, AFs were induced by treating CCD-18Co cells with transforming growth factor-β1. BC treatment suppressed expression of fibroblast activation markers. In addition, conditioned media from BC-treated M2 macrophages and AF inhibited cancer stem cell markers, colon cancer cell invasiveness and migration, and the epithelial-mesenchymal transition (EMT). In vivo, BC supplementation inhibited tumor formation and the expression of M2 macrophage markers in an azoxymethane/dextran sodium sulfate-induced colitis-associated CRC mouse model. To our knowledge, the present findings provide the first evidence suggesting that the potential therapeutic effects of BC on CRC are mediated by the inhibition of M2 macrophage polarization and fibroblast activation.     

Regulation of thrombospondin-1 expression in alternatively activated macrophages and adipocytes: role of cellular cross talk and omega-3 fatty acids

Thrombospondin-1 (TSP-1) expression in human adipose positively correlates with body mass index and may contribute to adipose dysfunction by activating transforming growth factor-β and/or inhibiting angiogenesis. Our objective was to determine how TSP-1 is regulated in adipocytes and polarized macrophages using a coculture system and to determine whether fatty acids, including the ω-3 fatty acid docosahexaenoic acid (DHA), regulate TSP-1 expression. Coculture of M1, M2a or M2c macrophages with adipocytes induced TSP-1 gene expression in adipocytes (from 2.4- to 4.2-fold, P<.05), and adipocyte coculture induced TSP-1 gene expression in M1 and M2c macrophages (M1: 8.6-fold, M2c: 26-fold; P<.05). TSP-1 protein levels in the shared media of adipocytes and M2c cells were also strongly induced by coculture (>10-fold, P<.05). DHA treatment during the coculture of adipocytes and M2c macrophages potently inhibited the M2c macrophage TSP-1 mRNA level (97% inhibition, P<.05). Adipocyte coculture induced interleukin (IL)-10 expression in M2c macrophages (10.1-fold, P<.05), and this increase in IL-10 mRNA expression was almost completely blocked with DHA treatment (96% inhibition, P<.05); thus, IL-10 expression closely paralleled TSP-1 expression. Since IL-10 has been shown to regulate TSP-1 in other cell types, we reduced IL-10 expression with siRNA in the M2c cells and found that this caused TSP-1 to be reduced in response to adipocyte coculture by 60% (P<.05), suggesting that IL-10 regulates TSP-1 expression in M2c macrophages. These results suggest that supplementation with dietary ω-3 fatty acids could potentially be beneficial to adipose tissue in obesity by reducing TSP-1 and fibrosis.     

Low density receptor-related protein 1 (LRP1) promotes anti-inflammatory phenotype in murine macrophages

We have previously reported that apolipoprotein E (apoE), a protein component of very-low-density lipoproteins (VLDL) and high-density lipoproteins and a potent plasma-borne atheroprotective factor, exerts anti-inflammatory activity in macrophages by switching the activation profile from M1 (“classic”) to M2 (“alternative”) in a process involving signaling via low-density lipoprotein receptor (LDLR) family members including the VLDL receptor (VLDLR) or apoE receptor-2 (apoER2). The present study was undertaken to investigate whether LDLR-related protein 1 (LRP-1), another member of the LDLR family and a ubiquitously expressed multifunctional cell surface receptor, modulates M1→M2 conversion in murine macrophages. We investigate bone marrow or peritoneal macrophages isolated from wild-type C57/Bl6 mice or mice with conditional inactivation of the LRP-1 gene in the myeloid lineage for the expression of polarization markers. Our results suggest that the deficiency of LRP-1 down-regulates M2 marker expression in macrophages, while enhancing the macrophage response to M1 stimuli. To our knowledge, this is the first demonstration that LRP-1 affects macrophage polarization and promotes the development of an anti-inflammatory M2 functional phenotype.     

Overexpression of IL-10 in C2D Macrophages Promotes a Macrophage Phenotypic Switch in Adipose Tissue Environments

Adipose tissue macrophages are a heterogeneous collection of classically activated (M1) and alternatively activated (M2) macrophages. Interleukin 10 (IL-10) is an anti-inflammatory cytokine, secreted by a variety of cell types including M2 macrophages. We generated a macrophage cell line stably overexpressing IL-10 (C2D-IL10) and analyzed the C2D-IL10 cells for several macrophage markers after exposure to adipocytes compared to C2D cells transfected with an empty vector (C2D-vector). C2D-IL10 macrophage cells expressed more CD206 when co-cultured with adipocytes than C2D-vector cells; while the co-cultured cell mixture also expressed higher levels of Il4, Il10, Il1β and Tnf. Since regular C2D cells traffic to adipose tissue after adoptive transfer, we explored the impact of constitutive IL-10 expression on C2D-IL10 macrophages in adipose tissue in vivo. Adipose tissue-isolated C2D-IL10 cells increased the percentage of CD206⁺, CD301⁺, CD11c⁻CD206⁺ (M2) and CD11c⁺CD206⁺ (M1b) on their cell surface, compared to isolated C2D-vector cells. These data suggest that the expression of IL-10 remains stable, alters the C2D-IL10 macrophage cell surface phenotype and may play a role in regulating macrophage interactions with the adipose tissue.     

A comparative study on root and bark extracts of Eleutherococcus senticosus and their effects on human macrophages

BackgroundEleutherococcus senticosus or Siberian ginseng is a medicinal plant containing adaptogenic substances believed to regulate immune responses. Both, the root and stem bark are commonly used in traditional medicines.PurposeThe purpose of the present study is to chemically characterize E. senticosus root and bark extracts and to compare their effects on functions of human primary macrophages.Study design and methodsHPLC-DAD-MS analysis was used to characterize chemical constituents of alcoholic extracts from E. senticosus root and bark. The data obtained and available databases were combined for network pharmacology analysis. Involvement of predicted pathways was further functionally confirmed by using monocyte-derived human macrophages and endotoxin-free E. senticosus root and bark extracts.ResultsChemical analysis showed that the root extract contained more syringin, caffeic acid, and isofraxidin than the bark extract. At variance, bark extract contained more sesamin and oleanolic acid. Coniferyl aldehyde and afzelin were below the limit of quantification in both extracts. Network pharmacology analysis indicated that constituents of E. senticosus might affect the immune cell phenotype and signaling pathways involved in cell metabolism and cytoskeleton regulation. Indeed, both extracts promoted actin polymerization, migration, and phagocytosis of E. coli by macrophages pointing to macrophage polarization towards the M2 phenotype. In addition, treatment with E. senticosus root and bark extracts decreased phosphorylation of Akt on Ser473 and significantly reduced expression of the hemoglobin scavenger receptor CD163 by macrophages. Neither extract affected expression of CD11b, CD80, or CD64 by macrophages. In addition, macrophages treated with the bark extract, but not with the root extract, exhibited activated p38 MAPK and NF-κB and released increased, but still moderate, amounts of proinflammatory TNF-α and IL-6, anti-inflammatory IL-10, and chemotactic CCL1, which all together point to a M2b-like macrophage polarization. Differently, the root extract increased the IL-4-induced expression of anti-inflammatory CD200R. These changes in monocytes are in agreement with an increased M2a macrophage polarization.ConclusionThe ability of E. senticosus root and bark extracts to promote polarization of human macrophages towards anti-inflammatory M2a and M2b phenotypes, respectively, might underlay the immunoregulatory activities and point to potential wound healing promoting effects of this medicinal plant.     

Tumor-associated macrophages in direct contact with prostate cancer cells promote malignant proliferation and metastasis through NOTCH1 pathway

Background: M2 macrophages are well accepted to promote cancer progression in the prostate cancer (PCa). Paracrine is the principally studied mode of communication between M2 macrophages and tumor cells. In addition to this, we present here a novel model to demonstrate these cellular communications.Methods: PCa cells were co-cultured with THP-1/ human peripheral blood mononuclear cells derived M2 macrophages in direct contact manner. Cancer cell proliferation and invasion were examined to explain how direct contact communicates. Cell-based findings were validated in two xenograft models and patients samples.Results: M2 macrophage direct contact induced a higher proliferation and invasion in PCa cells when compared with noncontact coculture manner. In direct contact manner, NOTCH1 pathway was greatly activated in PCa cells, induced by elevated γ-secretase activity and higher coactivator MAML2 expression. Additionally, blocking γ-secretase activity and depletion of MAML2 completely abolished M2 macrophage direct contact-mediated PCa cell proliferation and invasion. In vivo, inhibiting NOTCH1 signalling impaired M2 macrophage-mediated PCa tumor growth and lung metastasis. Notably, M2 macrophage infiltration as well as high NOTCH1 signaling in cancer cells indicated more aggressive features and worse survival in PCa patients.Conclusion: Our results demonstrated the cell-cell direct contact pattern is an important way in PCa microenvironment cell communication. In this manner, elevated γ-secretase activity and MAML2 expression induced higher NOTCH1 signalling in PCa cells, which increased tumor cells proliferation and invasion. This potentially provided a therapeutic target for PCa.