Identification of novel human CC chemokine receptor 8 (CCR8) antagonists via the synthesis of naphthalene amide and sulfonamide isosteres.

The human CC chemokine receptor 8 (CCR8) has been extensively pursued as target for the treatment of various inflammatory disorders. More recently, the importance of CCR8 in the tumor microenvironment has been demonstrated, spurring the interest in CCR8 antagonism as therapeutic strategy in immuno-oncology. On a previously described naphthalene sulfonamide with CCR8 antagonistic properties, the concept of isosterism was applied, leading to the discovery of novel CCR8 antagonists with IC50 values in the nM range in both the CCL1 competition binding and CCR8 calcium mobilization assay. The excellent CCR8 antagonistic activity of the most potent congeners was rationalized by homology molecular modeling.

Structural basis of antibody inhibition and chemokine activation of the human CC chemokine receptor 8.

The C-C motif chemokine receptor 8 (CCR8) is a class A G-protein coupled receptor that has emerged as a promising therapeutic target in cancer. Targeting CCR8 with an antibody has appeared to be an attractive therapeutic approach, but the molecular basis for chemokine-mediated activation and antibody-mediated inhibition of CCR8 are not fully elucidated. Here, we obtain an antagonist antibody against human CCR8 and determine structures of CCR8 in complex with either the antibody or the endogenous agonist ligand CCL1. Our studies reveal characteristic antibody features allowing recognition of the CCR8 extracellular loops and CCL1-CCR8 interaction modes that are distinct from other chemokine receptor - ligand pairs. Informed by these structural insights, we demonstrate that CCL1 follows a two-step, two-site binding sequence to CCR8 and that antibody-mediated inhibition of CCL1 signaling can occur by preventing the second binding event. Together, our results provide a detailed structural and mechanistic framework of CCR8 activation and inhibition that expands our molecular understanding of chemokine - receptor interactions and offers insight into the development of therapeutic antibodies targeting chemokine GPCRs.

The chemokine CCL1 facilitates pulmonary fibrosis by promoting macrophage migration and M2 polarization.

Macrophage M2 polarization has been identified in the pathogenesis of pulmonary fibrosis (PF), but the mediators that drive the macrophage M2 program in PF need to be clarified. We showed that the expression of AMFR and CCR8, two known receptors of CCL1, was increased in macrophages from lungs of mice with bleomycin (BLM)-induced PF. Deficiency in either AMFR or CCR8 in macrophages protected mice from BLM-induced PF. In vitro experiments revealed that CCL1 recruited macrophages by binding to its classical receptor CCR8 and drove the macrophage M2 phenotype via its interaction with the recently identified receptor AMFR. Mechanistic studies revealed that the CCL1-AMFR interaction enhanced CREB/C/EBPß signaling to promote the macrophage M2 program. Together, our findings reveal that CCL1 acts as a mediator of macrophage M2 polarization and could be a therapeutic target in PF.

Tumor-derived exosomes drive pre-metastatic niche formation in lung via modulating CCL1+ fibroblast and CCR8+ Treg cell interactions.

BACKGROUND: Since the lung is one of the most common sites for cancer metastasis, it could provide a suitable microenvironment for pre-metastatic niche (PMN) formation to facilitate tumor cell colonization. Regulatory T cells (Tregs) are an immunosuppressive cell type found ubiquitously in tumors and may play a crucial role in PNM formation. In this study, we investigated tumor-derived exosome (TDE)-induced Treg differentiation in the lung PMN as well as the underlying mechanisms. METHODS: TDEs were isolated from the Lewis lung carcinoma cell line (LLC-exo) and their effects on mouse pulmonary fibroblasts was investigated in vitro as well as on lung tumor formation and metastasis in a pre-injected mouse model. Immune cell populations in the lung were analyzed by flow cytometry. Expression of CCL1 and CCR8 was evaluated by immunofluorescence staining, qRT-PCR and Western blot analyses. Cytokine expression was measured using mouse cytokine arrays and ELISA. RESULTS: The number of CD4+ FoxP3+ Tregs was significantly increased in lungs in a LLC-exo pre-injected mouse model. Lung fibroblasts secreted increased amounts of CCL1 after co-culture with LLC-exo, which induced Treg differentiation by activating its specific receptor CCR8, ultimately contributing to the establishment of an immunologically tolerant PMN. Moreover, inhibiting the release of LLC-exo by GW4869, or blocking the CCL1-CCR8 axis using AZ084, suppressed Tregs differentiation and tumor metastasis in the lung. CONCLUSIONS: Collectively, our study provides a novel mechanism by which Tregs are activated to form an immunologically tolerant PMN and demonstrates a critical link among lung fibroblasts, Tregs and metastatic tumor cells.

The chemokine CCL1 triggers an AMFR-SPRY1 pathway that promotes differentiation of lung fibroblasts into myofibroblasts and drives pulmonary fibrosis.

Recruitment of immune cells to the site of inflammation by the chemokine CCL1 is important in the pathology of inflammatory diseases. Here, we examined the role of CCL1 in pulmonary fibrosis (PF). Bronchoalveolar lavage fluid from PF mouse models contained high amounts of CCL1, as did lung biopsies from PF patients. Immunofluorescence analyses revealed that alveolar macrophages and CD4+ T cells were major producers of CCL1 and targeted deletion of Ccl1 in these cells blunted pathology. Deletion of the CCL1 receptor Ccr8 in fibroblasts limited migration, but not activation, in response to CCL1. Mass spectrometry analyses of CCL1 complexes identified AMFR as a CCL1 receptor, and deletion of Amfr impaired fibroblast activation. Mechanistically, CCL1 binding triggered ubiquitination of the ERK inhibitor Spry1 by AMFR, thus activating Ras-mediated profibrotic protein synthesis. Antibody blockade of CCL1 ameliorated PF pathology, supporting the therapeutic potential of targeting this pathway for treating fibroproliferative lung diseases.

Hsa_circ_0134111 promotes osteoarthritis progression by regulating miR-224-5p/CCL1 interaction.

Mechanical, metabolic, inflammatory, and immune factors contribute to the development of osteoarthritis (OA), a joint disease characterized by cartilage destruction. The circular RNA (circRNA) hsa_circ_0134111 is upregulated in the cartilage of OA patients; however, its potential role in OA pathogenesis and progression remains unexplored. In this study, the effects of hsa_circ_0134111 knockdown were evaluated in primary human chondrocytes treated with IL-1ß to simulate OA, as well as in a rat model of OA. Hsa_circ_0134111 expression was upregulated in IL-1ß-stimulated chondrocytes. CCK-8 and flow cytometry assays showed that hsa_circ_0134111 knockdown reversed IL-1ß-induced cell decline by inhibiting apoptosis. Following prediction analysis of circRNA and miRNA targets, dual-luciferase reporter and silencing/overexpression assays suggested that a regulatory network composed of hsa_circ_0134111, miR-224-5p, and CCL1 modulates IL-1ß-mediated OA-like effects in chondrocytes. Accordingly, CCL1 overexpression abrogated the prosurvival effects of hsa_circ_0134111 knockdown in vitro. Moreover, hsa_circ_0134111 silencing in vivo alleviated cartilage destruction in an OA rat model, decreased IL-6 and TNF-α levels in synovial fluid, and downregulated CCL1 expression in the affected joints. These results suggest that hsa_circ_0134111 contributes to OA development by binding to miR-224-5p, thereby releasing the inhibition that miR-224-5p exerts over CCL1.

Biological characterization of ligands targeting the human CC chemokine receptor 8 (CCR8) reveals the biased signaling properties of small molecule agonists.

The human CC chemokine receptor 8 (CCR8) is a promising drug target for cancer immunotherapy and autoimmune disease. Besides human and viral chemokines, previous studies revealed diverse classes of CCR8-targeting small molecules. We characterized a selection of these CCR8 ligands (hCCL1, vCCL1, ZK756326, AZ6; CCR8 agonists and a naphthalene-sulfonamide-based CCR8 antagonist), in in vitro cell-based assays (hCCL1AF647 binding, calcium mobilization, cellular impedance, cell migration, ß-arrestin 1/2 recruitment), and used pharmacological tools to determine G protein-dependent and -independent signaling pathways elicited by these ligands. Our data reveal differences in CCR8-mediated signaling induced by chemokines versus small molecules, which was most pronounced in cell migration studies. Human CCL1 most efficiently induced cell migration whereby Gßγ signaling was indispensable. In contrast, Gßγ signaling did not contribute to cell migration induced by other CCR8 ligands (vCCL1, ZK756326, AZ6). Although all tested CCR8 agonists were full agonists for calcium mobilization, a significant contribution for Gßγ signaling herein was only apparent for human and viral CCL1. Despite both Gαi- and Gαq-signaling regulate intracellular Ca2+-release, cellular impedance experiments showed that CCR8 agonists predominantly induce Gαi-dependent signaling. Finally, small molecule agonists displayed higher efficacy in ß-arrestin 1 recruitment, which occurred independently of Gαi signaling. Also in this latter assay, only hCCL1-induced activity was dependent on Gßγ-signaling. Our study provides insight into CCR8 signaling and function and demonstrates differential CCR8 activation by different classes of ligands. This reflects the ability of CCR8 small molecules to evoke different subsets of the receptor's signaling repertoire, which categorizes them as biased agonists.

Macrophage-polarizing stimuli differentially modulate the inflammatory profile induced by the secreted phospholipase A2 group IA in human lung macrophages.

In this study we investigated the effects of snake venom Group IA secreted phospholipase A2 (svGIA) on the release of inflammatory and angiogenic mediators from human lung macrophages (HLMs). HLMs were incubated with lipopolysaccharide (LPS) or svGIA with or without macrophage-polarizing stimuli (IL-4, IL-10, IFN-γ or the adenosine analogue NECA). M2-polarizing cytokines (IL-4 and IL-10) inhibited TNF-α, IL-6, IL-12, IL-1ß, CXCL8 and CCL1 release induced by both LPS and svGIA. IL-4 inhibited also the release of IL-10. IFN-γ reduced IL-10 and IL-12 and increased CCL1 release by both the LPS and svGIA-stimulated HLMs, conversely IFN-γ reduced IL-1ß only by svGIA-stimulated HLMs. In addition, IFNγ promoted TNF-α and IL-6 release from svGIA-stimulated HLMs to a greater extent than LPS. NECA inhibited TNF-α and IL-12 but promoted IL-10 release from LPS-stimulated HLMs according to the well-known effect of adenosine in down-regulating M1 activation. By contrast NECA reduced TNF-α, IL-10, CCL1 and IL-1ß release from svGIA-activated HLM. IL-10 and NECA increased both LPS- and svGIA-induced vascular endothelial growth factor A (VEGF-A) release. By contrast, IL-10 reduced angiopoietin-1 (ANGPT1) production from activated HLMs. IFN-γ and IL-4 reduced VEGF-A and ANGPT1 release from both LPS- and svGIA-activated HLMs. Moreover, IL-10 inhibited LPS-induced ANGPT2 production. In conclusion, we demonstrated a fine-tuning modulation of svGIA-activated HLMs differentially exerted by the classical macrophage-polarizing cytokines.

Ectosomal PKM2 Promotes HCC by Inducing Macrophage Differentiation and Remodeling the Tumor Microenvironment.

Tumor-derived extracellular vesicles are important mediators of cell-to-cell communication during tumorigenesis. Here, we demonstrated that hepatocellular carcinoma (HCC)-derived ectosomes remodel the tumor microenvironment to facilitate HCC progression in an ectosomal PKM2-dependent manner. HCC-derived ectosomal PKM2 induced not only metabolic reprogramming in monocytes but also STAT3 phosphorylation in the nucleus to upregulate differentiation-associated transcription factors, leading to monocyte-to-macrophage differentiation and tumor microenvironment remodeling. In HCC cells, sumoylation of PKM2 induced its plasma membrane targeting and subsequent ectosomal excretion via interactions with ARRDC1. The PKM2-ARRDC1 association in HCC was reinforced by macrophage-secreted cytokines/chemokines in a CCL1-CCR8 axis-dependent manner, further facilitating PKM2 excretion from HCC cells to form a feedforward regulatory loop for tumorigenesis. In the clinic, ectosomal PKM2 was clearly detected in the plasma of HCC patients. This study highlights a mechanism by which ectosomal PKM2 remodels the tumor microenvironment and reveals ectosomal PKM2 as a potential diagnostic marker for HCC.

The utility of serum C-C chemokine ligand 1 in sarcoidosis: A comparison to IgG4-related disease.

We previously reported higher levels of C-C chemokine ligand (CCL) 1 in the bronchoalveolar lavage (BAL) fluid (BALF) of patients with sarcoidosis than in BALF of patients with immunoglobulin G4 (IgG4)-related disease (IgG4-RD), indicating that CCL1 might act as a marker of disease activity in sarcoidosis. Notably, less invasive sampling sources are desirable, as BAL cannot always be performed due to its inherent risk. In this study, we sought to decipher the correlation between serum levels of CCL1 and clinical characteristics of sarcoidosis. Serum samples were obtained from 44 patients with clinically confirmed sarcoidosis, 14 patients with IgG4-RD, and 14 healthy controls. The clinical and radiological findings were retrospectively evaluated. Serum levels of CCL1 were measured using a sandwich enzyme-linked immunosorbent assay. Serum levels of other 17 cytokines and chemokines were measured using a MILLIPLEX® MAP KIT and Luminex® magnetic beads. Serum levels of CCL1 were significantly higher in patients with sarcoidosis than in patients with IgG4-RD and healthy controls. Serum CCL1 was positively correlated with the degree of hilar lymph node swelling on chest computed tomography and serum levels of soluble interleukin 2 receptor. Positive correlations were also observed between serum CCL1 and total cell counts, lymphocyte counts in BALF, and serum T helper 1 mediators such as IP-10 and TNF-α in patients with sarcoidosis. Serum CCL1 levels were significantly elevated in sarcoidosis and correlated with clinical parameters of the disease. In addition, serum and BALF levels of CCL1 were positively correlated in a statistically significant manner. Although further research in this field is necessary, CCL1 might have the potential to be a reliable serological marker of disease activity in sarcoidosis.

Gadolinium causes M1 and M2 microglial apoptosis after intracerebral haemorrhage and exerts acute neuroprotective effects.

OBJECTIVES: Gadolinium (Gd) affects microglial polarization during remyelination. We previously reported that the suppression of proinflammatory microglia was neuroprotective in intracerebral haemorrhage (ICH). The objective of the present study was to investigate the effects of Gd on microglial polarization and neuronal injury after ICH. METHODS: Gadolinium was intraperitoneally administered to ICH mice prepared by an intrastriatal microinjection of collagenase type VII. The polarization of M1, 2a, b and c microglia was evaluated by real-time PCR using the respective markers. Changes in representative mRNAs were also confirmed by immunological methods. Neuroprotective effects were evaluated by counting NeuN-positive cells and a behavioural analysis. KEY FINDINGS: One day after ICH, the mRNA levels of proinflammatory M1 microglial markers, such as inducible nitric oxide synthase (iNOS), and anti-inflammatory M2 microglial markers, such as arginase1 (M2a, c), Ym1 (M2a), and transforming growth factor-ß (M2c), increased, while those of chemokine CCL1 (M2b) only increased after 3 days. Gd decreased the levels of all M1 and M2 markers. Arginase1 and iNOS protein levels also increased, and Gd reduced them due to apoptotic cell death. Gadolinium attenuated oedema, neuron loss, neurological deficits and the mortality rate without affecting haematoma sizes. CONCLUSIONS: Gadolinium induced M1 and M2 microglial apoptosis and exerted acute neuroprotective effects after ICH.

Spinal CCL1/CCR8 regulates phosphorylation of GluA1-containing AMPA receptor in postoperative pain after tibial fracture and orthopedic surgery in mice.

Chronic postoperative pain might be a pivotal component hindering recovery and regains the function after bone fracture and orthopedic surgery. However, the underlying mechanisms remain largely unclear. AMPA receptor of excitatory synapses is considered due to its critical role in pathologic pain. Chemokine CCL1 related neuroinflammation plays a role in excitatory synaptic transmission and nociceptive transduction. This study examined whether spinal CCL1 is associated with fracture-associated postoperative pain via AMPA receptor. We herein discovered that the tibial fracture with orthopedic surgery initiated and maintained chronic postoperative pain along with spinal up-regulation of CCL1/CCR8 expression and phosphorylation of GluA1-containing AMPA receptor. Central CCL1/CCR8 inhibition impaired mechanical and cold allodynia, and phosphorylated GluA1-containing AMPA receptor in the spinal dorsal horn. Intrathecal injection of GluA1-containing AMPA receptor antagonist NASPM alleviated fracture-related postoperative pain. Also, exogenous CCL1 delivery facilitated acute pain behaviors and spinal phosphorylation of GluA1-containing AMPA receptor in naïve mice, reversing by co-application of NASPM. Our current results indicated that spinal CCL1/CCR8-mediated GluA1-containing AMPA receptor activation is vital in the pathogenesis of fracture associated postoperative pain in mice.

A natural bioactive feed additive alters expression of genes involved in inflammation in whole blood of healthy Angus heifers.

A greater demand for food animal production without antibiotics has created the common practice of feeding food animals dietary immunomodulatory feed additives (IFA) throughout their life cycle. However, little is known about the impact of IFA on cytokine and chemokine signaling in non-stressed, non-pathogen-challenged food animals during the early feeding period. We evaluated the expression of 82 genes related to cytokine and chemokine signaling in the whole blood of growing Angus heifers to determine the effect of IFA supplementation on cytokine and chemokine signaling during the first 28 d of feeding. One gene (CCL1) was significantly up-regulated and 14 genes (17%) were significantly down-regulated by IFA feeding during the entire early feeding period including 5 of 21 (24%) evaluated chemokine and IL receptors (CCR1, CCR2, IL1R1, IL10RA, IL10RB). These data when taken together suggest providing an IFA in the diet of growing beef cattle during the early feeding period may suppress the inflammatory response through cytokine-cytokine receptor signaling.

Tumour exosomal CEMIP protein promotes cancer cell colonization in brain metastasis.

The development of effective therapies against brain metastasis is currently hindered by limitations in our understanding of the molecular mechanisms driving it. Here we define the contributions of tumour-secreted exosomes to brain metastatic colonization and demonstrate that pre-conditioning the brain microenvironment with exosomes from brain metastatic cells enhances cancer cell outgrowth. Proteomic analysis identified cell migration-inducing and hyaluronan-binding protein (CEMIP) as elevated in exosomes from brain metastatic but not lung or bone metastatic cells. CEMIP depletion in tumour cells impaired brain metastasis, disrupting invasion and tumour cell association with the brain vasculature, phenotypes rescued by pre-conditioning the brain microenvironment with CEMIP+ exosomes. Moreover, uptake of CEMIP+ exosomes by brain endothelial and microglial cells induced endothelial cell branching and inflammation in the perivascular niche by upregulating the pro-inflammatory cytokines encoded by Ptgs2, Tnf and Ccl/Cxcl, known to promote brain vascular remodelling and metastasis. CEMIP was elevated in tumour tissues and exosomes from patients with brain metastasis and predicted brain metastasis progression and patient survival. Collectively, our findings suggest that targeting exosomal CEMIP could constitute a future avenue for the prevention and treatment of brain metastasis.

A CCL1/CCR8-dependent feed-forward mechanism drives ILC2 functions in type 2-mediated inflammation.

Group 2 innate lymphoid cells (ILC2s) possess indispensable roles during type 2-mediated inflammatory diseases. Although their physiological and detrimental immune functions seem to depend on the anatomical compartment they reside, their tissue tropism and the molecular and immunological processes regulating the self-renewal of the local pool of ILC2s in the context of inflammation or infection are incompletely understood. Here, we analyzed the role of the CC-chemokine receptor CCR8 for the biological functions of ILC2s. In vitro and in vivo experiments indicated that CCR8 is in comparison to the related molecule CCR4 less important for migration of these cells. However, we found that activated mouse and human ILC2s produce the CCR8 ligand CCL1 and are a major source of CCL1 in vivo. CCL1 signaling to ILC2s regulates their proliferation and supports their capacity to protect against helminthic infections. In summary, we identify a novel chemokine receptor-dependent mechanism by which ILC2s are regulated during type 2 responses.

Peritumoural CCL1 and CCL22 expressing cells in hepatocellular carcinomas shape the tumour immune infiltrate.

Development, course of disease and prognosis of hepatocellular carcinomas (HCC) are strongly influenced by the immune system. Immunosuppressive regulatory T cells (Treg) have been shown to negatively impact disease progression and survival. To further understand the mechanisms of Treg attraction to HCC lesions, this study provides an analysis of Treg attracting chemokines in human HCC tissues. We analysed the expression of the Treg attracting chemokines CCL1 and CCL22 as well as the infiltration of FoxP3+ Treg and CD8+ T cells in paraffin-embedded tissue sections of 62 HCC patients. Expression of both chemokines was detected in 47 of 62 tissue slides. Chemokine expression was generally higher in tumour stroma and peritumoural liver tissue than in the tumour tissue itself. CD8+ T cells and FoxP3+ Treg were found at high levels in many tumour tissues. Intratumoural infiltration of Treg positively correlated with CCL22 levels in peritumoural liver tissue. In contrast, no correlation of Treg numbers and expression of CCL1 was detected. In summary, we describe here that the chemokines CCL1 and CCL22 are expressed in HCC tissues and, to a higher extent, in the stroma and peritumoural liver tissue. CCL22 may contribute to Treg recruitment and immunosuppression, whereas the role of CCL1 remains to be defined. It will be interesting to investigate the potential of these chemokines as drug targets for cancer therapy.

miR-21-5p inhibits neuropathic pain development via directly targeting C-C motif ligand 1 and tissue inhibitor of metalloproteinase-3.

MicroRNAs (miRNA) play important roles in neuroinflammation and neuropathic pain development; however, the underlying mechanism requires further investigation. The expression of miR-21-5p was remarkably upregulated in chronic constrictive injury (CCI) rat model. A significant alleviated neuropathic pain development and reduced the expression of cytokines was observed in CCI rat after exogenous injection of miR-21-5p mimic. The dual-luciferase analysis revealed that tissue inhibitor of metalloproteinase-3 (TIMP3) and chemokines C-C motif ligand 1 (CCL1) was direct downstream target of miR-21-5p. Moreover, silencing of TIMP3 and CCL1 could rescue mechanical allodynia, thermal hyperalgesia and cytokine release in CCI rat, suggesting that TIMP3 and CCL1 exert their function by mediating neuroinflammation in neuropathic pain development. Therefore, we have identified a novel miR-21-5p-CCL1/TIMP3-cytokine axis in regulation of neuropathic pain development in CCI rat model, which is valuable for enhancing our understanding of neuropathic pain and developing miRNAs as potential therapeutic options in the future.

Comparison of the chemokine profiles in the bronchoalveolar lavage fluid between IgG4-related respiratory disease and sarcoidosis: CC-chemokine ligand 1 might be involved in the pathogenesis of sarcoidosis.

BACKGROUND: We previously reported that the cytokine profiles in the bronchoalveolar lavage fluid (BALF) of IgG4-related respiratory disease (IgG4-RRD) more closely resemble the T-helper (Th) 2 response than sarcoidosis. The present study aimed to assess the chemokines in the BALF of IgG4-RRD and sarcoidosis in order to evaluate any possible associations between these chemokines and other markers. METHODS: We examined 12 chemokines using a MILLIPLEX® MAP Kit (Millipore, Darmstadt, Germany) in the same BALF samples of the same 44 patients (IgG4-RRD, n = 11; sarcoidosis, n = 33) in which we had previously evaluated the cytokines. RESULTS: The levels of CC-chemokine ligand (CCL)26 in the BALF of IgG4-RRD patients (median 24.5, range 3.1-401.1 pg/mL) were significantly higher than those in the BALF of sarcoidosis patients (median 3.1, range 3.1-155.6 pg/mL, p < 0.05). Interestingly, the BALF levels of CCL1 in the sarcoidosis patients (median 13.1, range 0.1-106.9 pg/mL) were significantly higher than those of the IgG4-RRD patients (median 9.8, range 0.1-14.7 pg/mL, p < 0.05). Furthermore, the CCL1 levels in the BALF were correlated with the total cell count (ρ = 0.539, p < 0.001), lymphocyte fraction (R = 0.406, P < 0.05), lymphocyte count (R = 0.686, P < 0.001), TNF-α level, (R = 0.748, P < 0.001), and IL-2 level (R = 0.757, P < 0.001) in the BALF of sarcoidosis patients. CONCLUSIONS: CCL1 might reflect disease activity and its involvement in the pathogenesis of sarcoidosis might be more closely related to Th1 than to Th2.

PPARγ Expression Is Diminished in Macrophages of Recurrent Miscarriage Placentas.

PPARγ belongs to the group of nuclear receptors which is expressed in the trophoblast and together with other factors is responsible for the maintenance of pregnancy. Apart from that PPARγ is also a main factor for macrophage polarization. The aim of this study was to investigate the combined expression pattern and frequency of PPARγ under physiological circumstances and in spontaneous and recurrent miscarriages in the trophoblast and in maternal macrophages of the decidua. Human placental tissues of the first trimester (15 physiologic pregnancies, 15 spontaneous abortion and 16 recurrent miscarriage placentas) were analyzed for expression of the nuclear receptor PPARγ. Expression changes were evaluated by immunohistochemistry and real time PCR (RT-PCR) in trophoblast and in maternal macrophages of the decidua. Maternal macrophages were identified by double immunofluorescence using cluster of differentiation 68 (CD68) as marker for macrophages and further characterized regarding their M1/M2 polarization status. The intermediate villous trophoblast revealed a significantly lower PPARγ expression in spontaneous and recurrent abortion. Maternal macrophages express PPARγ. Their number is significantly enhanced in the decidua of spontaneous miscarriages whereas in recurrent miscarriages maternal macrophages seem to express PPARγ only in very few cases. PPARγ is associated with an M2 polarization state that is common for decidual macrophages. The lack of PPARγ in recurrent miscarriage decidual macrophages seems to be associated with a specific inflammatory response against the fetus.