Functional differences between monocyte chemotactic protein-1 receptor A and monocyte chemotactic protein-1 receptor B expressed in a Jurkat T cell

Role of chemokine receptor 2 in rheumatoid arthritis: A research update

Rheumatoid arthritis (RA) is a multisystemic and inflammatory autoimmune disease characterized by joint destruction. The C-C motif chemokine receptor 2 (CCR2) is mainly expressed in monocytes and T cells, initiating their migration to sites of inflammation, ultimately leading to cartilage damage and bone destruction. CCR2 has long been considered a prospective target for treating autoimmune diseases. However, clinical studies on inhibitors or neutralizing antibodies against CCR2 in RA have exhibited limited efficacy. Recent evidence indicates that CCR2 may play different roles in RA. Hence, a comprehensive understanding regarding the role of CCR2 may facilitate the development of targeted drugs and provide novel insights for improving CCL2-mediated inflammatory diseases. This review summarizes the biological characteristics of CCR2, the related signaling pathways, and recent developments in CCR2-targeting therapeutics.

Combination therapy with bevacizumab and a CCR2 inhibitor for human ovarian cancer: An in vivo validation study

BACKGROUND

Anti-angiogenic therapy with bevacizumab (BEV), an anti-VEGF antibody, plays a critical role in the treatment of ovarian cancer. However, despite an encouraging initial response, most tumors become resistant to BEV over time, and a new strategy that enables sustainable treatment using BEV is therefore needed.

METHODS

To overcome the resistance to BEV in patients with ovarian cancer, we performed a validation study of combination therapy with BEV (10 mg/kg) and the CCR2 inhibitor BMS CCR2 22 (20 mg/kg) (BEV/CCR2i) using 3 consecutive patient-derived xenografts (PDXs) of immunodeficient mice.

RESULTS

BEV/CCR2i demonstrated a significant effect of growth suppression in the BEV-resistant serous PDX and BEV-sensitive serous PDX compared with BEV (30.4% after the second cycle and 15.5% after the first cycle, respectively), and treatment cessation did not attenuate this effect. Tissue clearing and immunohistochemistry with an anti-α-SMA antibody suggested that BEV/CCR2i suppressed angiogenesis from the host mice more than BEV. In addition, human CD31 immunohistochemistry revealed that BEV/CCR2i decreased microvessels originating from the patients to a significantly greater degree than BEV. Regarding the BEV-resistant clear cell PDX, the effect of BEV/CCR2i was unclear during the first five cycles, but the following two cycles of increased-dose BEV/CCR2i (CCR2i 40 mg/kg) significantly suppressed tumor growth compared with BEV (28.3%) by inhibiting the CCR2B-MAPK pathway.

CONCLUSIONS

BEV/CCR2i showed a sustained anticancer immunity-independent effect in human ovarian cancer that was more significant in serous carcinoma than in clear cell carcinoma.

Role of CCL2/CCR2 axis in the pathogenesis of COVID-19 and possible Treatments: All options on the Table

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is cause of the novel coronavirus disease (COVID-19). In the last two years, SARS-CoV-2 has infected millions of people worldwide with different waves, resulting in the death of many individuals. The evidence disclosed that the host immune responses to SARS-CoV-2 play a pivotal role in COVID-19 pathogenesis and clinical manifestations. In addition to inducing antiviral immune responses, SARS-CoV-2 can also cause dysregulated inflammatory responses characterized by the noticeable release of proinflammatory mediators in COVID-19 patients. Among these proinflammatory mediators, chemokines are considered a subset of cytokines that participate in the chemotaxis process to recruit immune and non-immune cells to the site of inflammation and infection. Researchers have demonstrated that monocyte chemoattractant protein-1 (MCP-1/CCL2) and its receptor (CCR2) are involved in the recruitment of monocytes and infiltration of these cells into the lungs of patients suffering from COVID-19. Moreover, elevated levels of CCL2 have been reported in the bronchoalveolar lavage fluid (BALF) obtained from patients with severe COVID-19, initiating cytokine storm and promoting CD163⁺ myeloid cells infiltration in the airways and further alveolar damage. Therefore, CCL2/CCR axis plays a key role in the immunopathogenesis of COVID-19 and targeted therapy of involved molecules in this axis can be a potential therapeutic approach for these patients. This review discusses the biology of the CCL2/CCR2 axis as well as the role of this axis in COVID-19 immunopathogenesis, along with therapeutic options aimed at inhibiting CCL2/CCR2 and modulating dysregulated inflammatory responses in patients with severe SARS-CoV-2 infection.

Targeting the CCL2/CCR2 Axis in Cancer Immunotherapy: One Stone, Three Birds?

CCR2 is predominantly expressed by monocytes/macrophages with strong proinflammatory functions, prompting the development of CCR2 antagonists to dampen unwanted immune responses in inflammatory and autoimmune diseases. Paradoxically, CCR2-expressing monocytes/macrophages, particularly in tumor microenvironments, can be strongly immunosuppressive. Thus, targeting the recruitment of immunosuppressive monocytes/macrophages to tumors by CCR2 antagonism has recently been investigated as a strategy to modify the tumor microenvironment and enhance anti-tumor immunity. We present here that beneficial effects of CCR2 antagonism in the tumor setting extend beyond blocking chemotaxis of suppressive myeloid cells. Signaling within the CCL2/CCR2 axis shows underappreciated effects on myeloid cell survival and function polarization. Apart from myeloid cells, T cells are also known to express CCR2. Nevertheless, tissue homing of Treg cells among T cell populations is preferentially affected by CCR2 deficiency. Further, CCR2 signaling also directly enhances Treg functional potency. Thus, although Tregs are not the sole type of T cells expressing CCR2, the net outcome of CCR2 antagonism in T cells favors the anti-tumor arm of immune responses. Finally, the CCL2/CCR2 axis directly contributes to survival/growth and invasion/metastasis of many types of tumors bearing CCR2. Together, CCR2 links to two main types of suppressive immune cells by multiple mechanisms. Such a CCR2-assoicated immunosuppressive network is further entangled with paracrine and autocrine CCR2 signaling of tumor cells. Strategies to target CCL2/CCR2 axis as cancer therapy in the view of three types of CCR2-expessing cells in tumor microenvironment are discussed.

Phenotypic characterization of MCP-1 expressing neurons in the rat cerebral cortex

Chemokines are small, secreted molecules that mediate inflammatory reactions. Neurons and astrocytes constitutively express chemokines implicated in the process of neuroinflammation associated with neurodegenerative diseases. The monocyte chemoattractant protein-1 (MCP-1) has been widely related to this process. However, the constitutive expression of this molecule by neurons has not been elucidated so far. In this study, we set out to characterize the neurochemical phenotype of MCP-1-expressing neurons in the rat neocortex to infer its role in basal conditions. We observed the presence of two populations of neurons expressing MCP-1: One population of cells with weak expression of MCP-1 corresponding to principal neurons (Tbr-1 positive) and a second population with high expression of MCP-1 corresponding to inhibitory neurons (GAD-67 positive), in particular to CCK/CBR1 interneurons. Moreover, high MCP-1-expressing neurons were metabolically active (pCREB positive). The population of CCK interneurons that co-localizes with MCP-1 corresponds to the regular-spiking basket cells and is co-responsible for the perisomatic inhibition of principal pyramidal neurons. Previous studies have demonstrated that MCP-1 can alter the electric properties of neurons and a tonic function for this molecule has been postulated. As CCK-inhibitory neurons are affected in mood disorders, whether the expression of MCP-1 was maintained in humans could be part of the link between inflammatory responses and observed changes in mood state.

Monocyte chemoattractant protein-1 (MCP-1/CCL2) in diabetic retinopathy: latest evidence and clinical considerations

Diabetic retinopathy (DR) is considered as a diabetes-related complication that can render severe visual impairments and is also a risk factor for acquired blindness in both developed as well as developing countries. Through fibrovascular epiretinal membranes (ERMs), this condition can similarly lead to tractional retinal detachment. Laboratory efforts evaluating the DR pathogenesis can be provided by ocular vitreous fluid and ERMs resulting from vitrectomy. The clinical stages of DR are significantly associated with expression levels of certain chemokines, including monocyte chemotactic protein-1 (MCP-1) in the intraocular fluid. The MCP-1 is also a known potent chemotactic factor for monocytes and macrophages that can stimulate them to produce superoxide and other mediators. Following hyperglycemia, retinal pigmented epithelial (RPE) cells, endothelial cells, and Müller's glial cells are of utmost importance for MCP-1 production, and vitreous MCP-1 levels rise in patients with DR. Increased expression of the MCP-1 in the eyes can also play a significant role in the pathogenesis of DR. In this review, current clinical and laboratory progress achieved on the MCP-1 and the DR concerning neovascularization and inflammatory responses in vitreous and/or aqueous humor of DR patients was summarized. It was suggested that further exploration of the MCP-1/CCR2 axis association between clinical stages of DR and expression levels of inflammatory and angiogenic cytokines and chemokines, principally the MCP-1 might lead to potential therapies aiming at neutralizing antibodies and viral vectors.

CCL2/CCR2 signaling pathway in glioblastoma multiforme

Glioblastoma multiform (GBM) is described as one of the most frequent primary brain tumors. These types of malignancies constitute only 15% of all primary brain tumors. Despite, extensive developments on effective therapeutic methods during the 20th century as well as the first decade of the present century (21st), the median survival rate for patients suffering from GBM is only approximately 15 months, even in response to multi-modal therapy. numerous types of reticuloendothelial system cells such as macrophages and microglial cells occupied within both GBM and also normal surrounding tissues. These immune cells acquire an otherwise activated phenotype with potent tumor-tropic functions that contribute to the glioma growth and invasion. The CC chemokine, CCL2 (previously named MCP-1) is of the most important CC chemokines family member involving in regulation of oriented migration and penetrative infiltration of mainly reticuloendothelial system cells specifically monocyte/macrophage phenotypes. Fundamental parts are played by CCL2 and its related receptor (the CCR2) in brain tumors and obviously in migration of monocytes from the bloodstream through the vascular endothelium. Therefore, CCL2/CCR2 axis is required for the routine immunological surveillance of tissues, in accordance with response to inflammation. Briefly, in this review, we have tried our best to collect the latest, straightened and summarize literature reports exist within data base regarding the interaction between microglia/macrophages and CCL2/CCR2 axis in GBM. We aimed to discuss potential application of this chemokine/receptor interaction axis for the expansion of future anti-glioma therapies as well.

CXC Chemokine Receptor 3 Alternative Splice Variants Selectively Activate Different Signaling Pathways

The G protein-coupled receptor (GPCR) C-X-C chemokine receptor 3 (CXCR3) is a potential drug target that mediates signaling involved in cancer metastasis and inflammatory diseases. The CXCR3 primary transcript has three potential alternative splice variants and cell-type specific expression results in receptor variants that are believed to have different functional characteristics. However, the molecular pharmacology of ligand binding to CXCR3 alternative splice variants and their downstream signaling pathways remain poorly explored. To better understand the role of the functional consequences of alternative splicing of CXCR3, we measured signaling in response to four different chemokine ligands (CXCL4, CXCL9, CXCL10, and CXCL11) with agonist activity at CXCR3. Both CXCL10 and CXCL11 activated splice variant CXCR3A. Whereas CXCL10 displayed full agonistic activity for Gαi activation and extracellular signal regulated kinase (ERK) 1/2 phosphorylation and partial agonist activity for β-arrestin recruitment, CXCL9 triggered only modest ERK1/2 phosphorylation. CXCL11 induced CXCR3B-mediated β-arrestin recruitment and little ERK phosphorylation. CXCR3Alt signaling was limited to modest ligand-induced receptor internalization and ERK1/2 phosphorylation in response to chemokines CXCL11, CXCL10, and CXCL9. These results show that CXCR3 splice variants activate different signaling pathways and that CXCR3 variant function is not redundant, suggesting a mechanism for tissue specific biased agonism. Our data show an additional layer of complexity for chemokine receptor signaling that might be exploited to target specific CXCR3 splice variants.

Targeting the CCL2-CCR2 signaling axis in cancer metastasis

The CCL2-CCR2 signaling axis has generated increasing interest in recent years due to its association with the progression of cancer. Although first described as a chemotactic molecule with physiological roles in regulating inflammation, recent studies have revealed a pro-tumorigenic function for CCL2 in favoring cancer development and subsequent metastasis. CCL2 binds the cognate receptor CCR2, and together this signaling pair has been shown to have multiple pro-tumorigenic roles, from mediating tumor growth and angiogenesis to recruiting and usurping host stromal cells to support tumor progression. The importance of CCL2-CCR2 signaling has been further championed by the establishment of clinical trials targeting this signaling pair in solid and metastatic cancers. Here we review the roles of CCL2-CCR2 signaling in the development and progression of cancer metastasis. We further evaluate the outcome of several clinical trials targeting either CCL2 or CCR2, and discuss the prospects and challenges of manipulating CCL2-CCR2 interaction as a potential approach for combating metastatic disease.

Senescence-Associated MCP-1 Secretion Is Dependent on a Decline in BMI1 in Human Mesenchymal Stromal Cells

AIMS

Cellular senescence and its secretory phenotype (senescence-associated secretory phenotype [SASP]) develop after long-term expansion of mesenchymal stromal cells (MSCs). Further investigation of this phenotype is required to improve the therapeutic efficacy of MSC-based cell therapies. In this study, we show that positive feedback between SASP and inherent senescence processes plays a crucial role in the senescence of umbilical cord blood-derived MSCs (UCB-MSCs).

RESULTS

We found that monocyte chemoattractant protein-1 (MCP-1) was secreted as a dominant component of the SASP during expansion of UCB-MSCs and reinforced senescence via its cognate receptor chemokine (c-c motif) receptor 2 (CCR2) by activating the ROS-p38-MAPK-p53/p21 signaling cascade in both an autocrine and paracrine manner. The activated p53 in turn increased MCP-1 secretion, completing a feed-forward loop that triggered the senescence program in UCB-MSCs. Accordingly, knockdown of CCR2 in UCB-MSCs significantly improved their therapeutic ability to alleviate airway inflammation in an experimental allergic asthma model. Moreover, BMI1, a polycomb protein, repressed the expression of MCP-1 by binding to its regulatory elements. The reduction in BMI1 levels during UCB-MSC senescence altered the epigenetic status of MCP-1, including the loss of H2AK119Ub, and resulted in derepression of MCP-1.

INNOVATION

Our results provide the first evidence supporting the existence of the SASP as a causative contributor to UCB-MSC senescence and reveal a so far unappreciated link between epigenetic regulation and SASP for maintaining a stable senescent phenotype.

CONCLUSION

Senescence of UCB-MSCs is orchestrated by MCP-1, which is secreted as a major component of the SASP and is epigenetically regulated by BMI1.

Synthesis, binding affinity and structure-activity relationships of novel, selective and dual targeting CCR2 and CCR5 receptor antagonists

CCR2 and CCR5 receptors play a key role in the development and progression of several inflammatory, cardiovascular and autoimmune diseases. Therefore, dual targeting of both receptors appeals as a promising strategy for the treatment of such complex, multifactorial disorders. Herein we report on the design, synthesis and biological evaluation of benzo[7]annulene- and [7]annulenothiophene-based selective and dual CCR2 and CCR5 receptor antagonists. Intermediates were designed in such a way that diversification could be introduced at the end of the synthesis. Starting from the lead compound TAK-779 (1), the quaternary ammonium moiety was exchanged by different non-charged moieties, the 4-methylphenyl moiety was extensively modified and the benzo[7]annulene core was replaced bioisosterically by the [7]annulenothiophene system. The naphthyl derivative 9h represents the most promising dual antagonist (Ki (CCR2) = 25 nM, IC50 (CCR5) = 17 nM), whereas the 6-isopropoxy-3-pyridyl and 4-methoxycarbonylphenyl derivatives 9k and 9r show more than 20-fold selectivity for the CCR2 (Ki = 19 nM) over the CCR5 receptor.

The protective effect of MCP-1 -2518 A>G promoter polymorphism in Turkish chronic renal failure patients requiring long-term hemodialysis

OBJECTIVE

Monocyte chemoattractant protein-1 (MCP-1) plays a major role in the pathogenesis and progression of different types of human renal disease. Therefore, in this study, we aimed to investigate the effect of MCP-1 gene -2518 A>G promoter polymorphism in chronic renal failure (CRF) patients requiring long-term hemodialysis.

METHODS

The study population consisted of 201 adult CRF patients requiring long-term hemodialysis and 194 healthy controls. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used for genotyping of MCP-1 -2518 A>G polymorphism in the CRF patients and healthy controls.

RESULTS

There were statistically significant differences in terms of genotypic (χ (2) = 12.69, p = 0.02) and allelic (χ (2) = 5.72, p = 0.02) frequencies of MCP-1 -2518 A>G between CRF patients and control subjects. According to our results, in the patient group MCP-1 -2518 AA genotype frequency was significantly higher than that of control group. On the other hand, heterozygous AG genotype frequency in the control group was significantly higher than that of the study group. Three different main disease subgroups of CRF (hypertension, diabetes mellitus, and atherosclerosis) patients were also evaluated, and significant associations were found between hypertension (genotype: χ (2) = 9.28, p = 0.01; allele: χ (2) = 6.00, p = 0.01), atherosclerosis (genotype: χ (2) = 5.37, p = 0.02; allele: χ (2) = 4.13, p = 0.04), and distributions of MCP-1 -2518 A>G genotypes and alleles. However, no significant association was found between diabetes mellitus and distributions of MCP-1 -2518 A>G genotype and allele frequencies (genotype: χ (2) = 2.37, p = 0.3; allele: χ (2) = 1.88, p = 0.17).

CONCLUSION

Current data show that MCP-1 -2518 AA genotype may cause susceptibility to CRF, while G allele may have a protective effect against development of CRF. In addition, MCP-1 -2518 AA genotype seems to associate with CRF originated from hypertension and atherosclerosis in our study population.

A MCP-1 promoter polymorphism at G-2518A is associated with spontaneous preterm birth

Monocyte chemoattractant protein-1 (MCP-1) is an important chemokine involved in the pathogenesis of spontaneous preterm birth (SPTB). We examined whether the MCP-1 G-2518A polymorphism is associated with the risk of SPTB in a Chinese population. The MCP-1 G-2518A polymorphism was genotyped in 569 preterm singleton neonates and in 673 term neonates using polymerase chain reaction-restriction fragment length polymorphism analysis. The distribution of the MCP-1 G-2518A genotype and the allele frequencies between the SPTB patients and the controls were not significantly different in the overall sample. However, we found that the AA genotype was associated with significantly increased susceptibility to very SPTB (<32 weeks) [odds ratio (OR) 2.07; 95 % confidence interval (CI), 1.27-3.36; P = 0.005) and extremely SPTB (<28 weeks) (OR 2.74; 95 % CI, 1.10-6.72; P = 0.014) compared with -2518G-positive genotypes (GG + GA genotypes). When extremely preterm neonates and very preterm neonates were combined, the AA genotype was also significantly associated with increased susceptibility to SPTB (OR 2.23; 95 % CI, 1.40-3.54; P < 0.001). The MCP-1 G-2518A polymorphism was not associated with increased susceptibility to SPTB in patients with premature rupture of the membranes (PROM) or in those without PROM. Our findings suggest that the MCP-1 G-2518A polymorphism may plays a role in mediating the susceptibility to SPTB in the Chinese population. Knowledge of genetic factors contributing to the pathogenesis of SPTB may have implications for screening and treatment of this disorder.

Stimulatory role of the chemokine CCL2 in the migration and peptide expression of embryonic hypothalamic neurons

Neuroinflammation is a feedback mechanism against infection, with recent studies suggesting a neuromodulatory role. The chemokine, (C-C motif) ligand 2 (CCL2), and its receptor, (C-C motif) receptor type 2 (CCR2), affect neuromodulation and migration in response to damage. Although CCL2 co-localizes with neuropeptides in the hypothalamus that control voluntary behavior, the function of CCL2/CCR2 is unknown. This led us to consider the possibility that CCL2 acting through CCR2, under natural conditions, may affect the migration and peptide levels of hypothalamic neurons that control voluntary behavior. This study used primary embryonic hypothalamic neurons to examine the effect of CCL2 on migratory behavior and on levels of the peptides, enkephalin (ENK) and galanin. Treatment with CCL2 led to a significant, dose-dependent increase in the number of migrated neurons and an increase in the velocity and distance traveled. CCL2 also significantly increased the number of ENK-expressing and CCR2/ENK co-expressing neurons and the percentage of neurons that contain higher levels of ENK. Lastly, CCL2 produced a dose-dependent increase in expression of ENK and galanin. These results provide evidence for a stimulatory effect of CCL2 on embryonic hypothalamic neurons involving changes in migratory behavior, expression, and synthesis of neuropeptides that function in controlling behavior. Our results demonstrate that the chemokine, CCL2, functions through its receptor, CCR2, to stimulate the migration and expression of the orexigenic peptides, enkephalin (ENK) and galanin (GAL), in developing embryonic hypothalamic neurons that are important for controlling ingestive behavior. This evidence reveals broad effects of CCL2 in the developing hypothalamus, showing this chemokine system to be tightly linked to the hypothalamic peptide neurons.

Monocyte chemoattractant protein-1 and the blood-brain barrier

The blood-brain barrier (BBB) is a dynamic structure that maintains the homeostasis of the brain and thus proper neurological functions. BBB compromise has been found in many pathological conditions, including neuroinflammation. Monocyte chemoattractant protein-1 (MCP1), a chemokine that is transiently and significantly up-regulated during inflammation, is able to disrupt the integrity of BBB and modulate the progression of various diseases, including excitotoxic injury and hemorrhage. In this review, we first introduce the biochemistry and biology of MCP1, and then summarize the effects of MCP1 on BBB integrity as well as individual BBB components.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXIX. Update on the extended family of chemokine receptors and introducing a new nomenclature for atypical chemokine receptors

Sixteen years ago, the Nomenclature Committee of the International Union of Pharmacology approved a system for naming human seven-transmembrane (7TM) G protein-coupled chemokine receptors, the large family of leukocyte chemoattractant receptors that regulates immune system development and function, in large part by mediating leukocyte trafficking. This was announced in Pharmacological Reviews in a major overview of the first decade of research in this field [Murphy PM, Baggiolini M, Charo IF, Hébert CA, Horuk R, Matsushima K, Miller LH, Oppenheim JJ, and Power CA (2000) Pharmacol Rev 52:145-176]. Since then, several new receptors have been discovered, and major advances have been made for the others in many areas, including structural biology, signal transduction mechanisms, biology, and pharmacology. New and diverse roles have been identified in infection, immunity, inflammation, development, cancer, and other areas. The first two drugs acting at chemokine receptors have been approved by the U.S. Food and Drug Administration (FDA), maraviroc targeting CCR5 in human immunodeficiency virus (HIV)/AIDS, and plerixafor targeting CXCR4 for stem cell mobilization for transplantation in cancer, and other candidates are now undergoing pivotal clinical trials for diverse disease indications. In addition, a subfamily of atypical chemokine receptors has emerged that may signal through arrestins instead of G proteins to act as chemokine scavengers, and many microbial and invertebrate G protein-coupled chemokine receptors and soluble chemokine-binding proteins have been described. Here, we review this extended family of chemokine receptors and chemokine-binding proteins at the basic, translational, and clinical levels, including an update on drug development. We also introduce a new nomenclature for atypical chemokine receptors with the stem ACKR (atypical chemokine receptor) approved by the Nomenclature Committee of the International Union of Pharmacology and the Human Genome Nomenclature Committee.

Ceramide 1-phosphate induces macrophage chemoattractant protein-1 release: involvement in ceramide 1-phosphate-stimulated cell migration

The bioactive sphingolipid ceramide 1-phosphate (C1P) is implicated in inflammatory responses and was recently shown to promote cell migration. However, the mechanisms involved in these actions are poorly described. Using J774A.1 macrophages, we have now discovered a new biological activity of C1P: stimulation of monocyte chemoattractant protein-1 (MCP-1) release. This novel effect of C1P was pertussis toxin (PTX) sensitive, suggesting the intervention of Gi protein-coupled receptors. Treatment of the macrophages with C1P caused activation of the phosphatidylinositol 3-kinase (PI3K)/Akt, mitogen-activated protein kinase kinase (MEK)/extracellularly regulated kinases (ERK), and p38 pathways. Inhibition of these kinases using selective inhibitors or specific siRNA blocked the stimulation of MCP-1 release by C1P. C1P stimulated nuclear factor-κB activity, and blockade of this transcription factor also resulted in complete inhibition of MCP-1 release. Also, C1P stimulated MCP-1 release and cell migration in human THP-1 monocytes and 3T3-L1 preadipocytes. A key observation was that sequestration of MCP-1 with a neutralizing antibody or treatment with MCP-1 siRNA abolished C1P-stimulated cell migration. Also, inhibition of the pathways involved in C1P-stimulated MCP-1 release completely blocked the stimulation of cell migration by C1P. It can be concluded that C1P promotes MCP-1 release in different cell types and that this chemokine is a major mediator of C1P-stimulated cell migration. The PI3K/Akt, MEK/ERK, and p38 pathways are important downstream effectors in this action.

Relationship between CCR2-V64I polymorphism and cancer risk: a meta-analysis

BACKGROUND AND OBJECTIVES

The role of CCR2-V64I polymorphism in various cancers has been reported in many studies. However, results from published studies on the association between CCR2-V64I polymorphism and cancer risk are conflicting. Therefore, we performed a meta-analysis to estimate the overall cancer risk associated with the polymorphism.

METHODS

Electronic searches of PubMed and EMBASE were conducted for all publications on the association between this variant and cancer. Odds ratios (OR) with 95% confidence intervals (95% CI) were used to access the strength of this association.

RESULTS

Sixteen studies with 2661 cancer patients and 5801 healthy controls were included. Overall, significant association was found between the CCR2-V64I polymorphism and cancer risk (OR=1.84, 95% CI=1.35-2.51, AA vs GA/GG, P=0.37). In the subgroup analysis stratified by cancer types, there was a significant association between this polymorphism and bladder cancer (OR=2.06, 95% CI=1.02-4.15, AA vs GA/GG, P=0.11), cervical cancer (OR=3.34, 95% CI=1.48-7.50, AA vs GG, P=0.56), and oral cancer (OR=2.04, 95% CI=1.46-2.84, GA vs GG, P=0.70). In the subgroup analysis stratified by ethnicities, an increased cancer risk was also found in Europeans (OR=2.31, 95% CI=1.45-3.68, AA vs GA/GG, P=0.16) and Asians (OR=1.88, 95% CI=1.12-3.16, AA vs GA/GG, P=0.92).

CONCLUSION

This meta-analysis suggested that CCR2-V64I polymorphism may contribute to an increased risk of cancer.

Membranar effects exerted in vitro by polyphenols - quercetin, epigallocatechin gallate and curcumin - on HUVEC and Jurkat cells, relevant for diabetes mellitus

Polyphenols are largely studied for their beneficial action in various pathologies, but the correlation with their effects on cell membranes is still elusive. In the present study we assessed the effects exerted in vitro by quercetin, epigallocatechin gallate and curcumin on membrane fluidity and transmembrane potential of human umbilical vein endothelial cells and Jurkat T lymphoblasts, in experimental conditions mimicking diabetes mellitus, i.e. high glucose conditions or increased concentration of advanced glycation end products. Results showed that the investigated polyphenols had beneficial effects on cell membranes altered in diabetic conditions, by restoring transmembrane potential and by membrane "stiffening". Moreover, they limited the release of pro-inflammatory factors, like monocyte chemotactic protein-1. These effects were more obvious for cells exposed to advanced glycation end products specific for the late stages of diabetes. Apparently, the inhibitory action of polyphenols on lipid peroxidation was associated with a decrease of membrane fluidity. Concluding, our in vitro study highlighted the potential beneficial action of polyphenols mainly in the late stages of diabetes, exerted at the level of membrane fluidity and transmembrane potential, accompanied by an anti-inflammatory effect on endothelial and immune cells.

Relationships of single nucleotide polymorphisms of monocyte chemoattractant protein 1 and chemokine receptor 2 with susceptibility and clinicopathologic characteristics of neoplasia of uterine cervix in Taiwan women

Few studies reported the implication of single nucleotide polymorphisms (SNPs) of monocyte chemoattractant protein 1 (MCP-1) and its receptor chemokine receptor 2 (CCR-2) in clinical significance of cancer of uterine cervix. We hypothesized that SNPs of MCP-1 and CCR-2 may affect the expression of these genes and then proteins. Therefore, we investigated the influence of the gene polymorphisms of MCP-1 and CCR-2 on the susceptibility and clinicopathologic characteristics of cervical neoplasia in Taiwan women. We recruited 86 patients with invasive cancer and 61 with high-grade dysplasia and 253 control women and selected 1 MCP-1 SNP rs1024611 (-2518G/A) and 1 CCR-2 SNP rs1799864 (190G/A; V64I) to determine their genotypes distribution using polymerase chain reaction-restriction fragment length polymorphism. In comparison to normal individuals with homozygotes GG in MCP-2 SNP, women with GA or AA carried a 2.01 odds ratio of developing cervical cancer. Nevertheless, it was not demonstrated in CCR-2 SNP. Furthermore, women with mutant homozygote (AA) of MCP-1 SNP increased the risk of deep stromal invasion, large tumor diameter, and parametrium invasion of cervical cancer, when compared to those with wild homozygote GG or heterozygote GA. However, women with mutant homozygotes (AA) of CCR-2 SNP did not increase the risk of poor clinicopathologic characteristics. In conclusion, MCP-1 SNP may be correlated with the development, deep stromal invasion, large tumor diameter, and parametrium invasion of cervical cancer but not with cancer recurrence or survival of Taiwan women patients with cancer. However, the SNP of its receptor, CCR-2, is not implicated in cervical cancer.

Genetic variants of the monocyte chemoattractant protein-1 gene and its receptor CCR2 and risk of coronary artery disease: a meta-analysis

OBJECTIVE

Monocyte chemoattractant protein-1 (MCP-1) and its receptor chemokine (C-C motif) receptor 2 (CCR2) are implicated in promoting atherosclerosis. Many studies have searched the association between variants of the MCP-1 gene or CCR2 gene and risk of coronary artery disease (CAD), but the results are inconsistent.

METHODS

We conducted a meta-analysis of 20 publications including 24 studies on 2 genetic variants [A-2518G in the MCP-1 and V64I in the CCR2] published before January 2011, including a total of 9844 patients with CAD and 11,821 controls. Publication bias and heterogeneity among studies were explored.

RESULTS

In a combined analysis, the pooled OR for CAD of the -2518G allele was 1.42 (95%CI: 1.06-1.92) compared to wild-type A allele under a recessive model in Caucasian group, but there is an indication of publication bias and heterogeneity among the 9 studies. When the analyses were restricted to 2 large studies (n≥500 cases), the pooled OR was 1.08 (95%CI: 0.85-1.37). Our analyses detected a possibility of publication bias with an overestimate of the true association by smaller studies. A meta-analysis of studies on the CCR2 V64I variant showed no significant association with CAD, the pooled OR of 64I was 1.27 (95%CI: 0.81-1.99) in recessive model and 1.06 (95%CI: 0.95-1.19) in dominant model, respectively.

CONCLUSIONS

The results indicate that MCP-1-2518G allele had probably increased risk of CAD in Caucasian but this is likely to be due to publication bias and insufficient sample size. The CCR2 V64I has not been found any association with CAD.

Polymorphisms in chemokine and receptor genes and gastric cancer risk and survival in a high risk Polish population

OBJECTIVE

To examine if genetic variations in chemokine receptor and ligand genes are associated with gastric cancer risk and survival.

METHODS

The study included 298 cases and 417 controls from a population-based study of gastric cancer conducted in Warsaw, Poland in 1994-1996. We investigated seven single nucleotide polymorphisms in a chemokine ligand (CXCL12) and chemokine receptor (CCR2, CCR5, CX3CR1) genes and one frameshift deletion (CCR5) in blood leukocyte DNA in relation to gastric cancer risk and survival. Genotyping was conducted at the NCI Core Genotyping Facility. Odds ratios and 95% confidence intervals were computed using univariate and multivariate logistic regression models. Survival analysis was performed using Cox proportional hazards models.

RESULTS

Gastric cancer risk was not associated with single chemokine polymorphisms. A CCR5 haplotype that contained the common alleles of IVS1+151 G>T (rs2734648), IVS2+80 C>T (rs1800024) and minor allele of IVS1+246 A>G (rs1799987) was associated with a borderline significantly increased risk (OR = 1.5, 95% CI: 1.0?2.2). For gastric cancer cases, there was a greater risk of death for carriers of the minor alleles of CCR2 Ex2+241 G>A (rs1799864) (HR = 1.5, 95% CI: 1.1-2.1) and CCR5 IVS2+80 C>T (rs1800024) (HR = 1.5, 95% CI: 1.1-2.1). Carriers of the CCR5 minor allele of IVS1+151 G>T (rs2734648) had a decreased risk of death compared to homozygote carriers of the common allele (HR = 0.8, 95% CI: 0.6-1.0).

CONCLUSIONS

Our findings do not support an association between gastric cancer risk and single chemokine genetic variation. The observed associations between cancer risk and a CCR5 haplotype and between survival and polymorphisms in CCR2 and CCR5 need replication in future studies.

Genetic polymorphism of CCR2-64I increased the susceptibility of hepatocellular carcinoma

BACKGROUND AND OBJECTIVES

The purpose of this study was to investigate genetic impact of monocyte chemoattractant protein-1 (MCP-1) and its receptor chemokine receptor-2 (CCR2) gene polymorphisms on the susceptibility and clinicopathological characteristics of hepatocellular carcinoma (HCC).

METHODS

A total of 446 subjects, including 344 healthy controls and 102 patients with HCC, were recruited in this study and subjected to PCR-RFLP to estimate the impact of these two polymorphic variants on HCC.

RESULTS

No relationship between MCP-1 -2518G/A gene polymorphism and HCC risk was found among our recruited HCC patients and healthy controls. However, there was a significantly increased risk (AOR = 1.91; 95% CI = 1.11-3.29) of having HCC among subjects with GA heterozygotes of CCR2 V64I after adjusting for other confoundings. There was no synergistic effect between gene polymorphism and environmental risk factors, including tobacco and alcohol consumptions, as well as clinicopathological parameters of HCC for MCP-1 -2518G/A and CCR2 V64I genes, respectively.

CONCLUSIONS

CCR2-64I gene polymorphism is an important factor for the susceptibility of HCC but it might not influence the clinical pathological progression of HCC, and the contribution of CCR2-64I gene polymorphism on the susceptibility of HCC could be not through the affection of liver injury-related clinical pathological characteristics.

Monocyte chemoattractant protein-1 (MCP-1): an overview

Chemokines constitute a family of chemoattractant cytokines and are subdivided into four families on the basis of the number and spacing of the conserved cysteine residues in the N-terminus of the protein. Chemokines play a major role in selectively recruiting monocytes, neutrophils, and lymphocytes, as well as in inducing chemotaxis through the activation of G-protein-coupled receptors. Monocyte chemoattractant protein-1 (MCP-1/CCL2) is one of the key chemokines that regulate migration and infiltration of monocytes/macrophages. Both CCL2 and its receptor CCR2 have been demonstrated to be induced and involved in various diseases. Migration of monocytes from the blood stream across the vascular endothelium is required for routine immunological surveillance of tissues, as well as in response to inflammation. This review will discuss these biological processes and the structure and function of CCL2.

Monocyte chemoattractant protein-1 (MCP-1): an overview

Chemokines constitute a family of chemoattractant cytokines and are subdivided into four families on the basis of the number and spacing of the conserved cysteine residues in the N-terminus of the protein. Chemokines play a major role in selectively recruiting monocytes, neutrophils, and lymphocytes, as well as in inducing chemotaxis through the activation of G-protein-coupled receptors. Monocyte chemoattractant protein-1 (MCP-1/CCL2) is one of the key chemokines that regulate migration and infiltration of monocytes/macrophages. Both CCL2 and its receptor CCR2 have been demonstrated to be induced and involved in various diseases. Migration of monocytes from the blood stream across the vascular endothelium is required for routine immunological surveillance of tissues, as well as in response to inflammation. This review will discuss these biological processes and the structure and function of CCL2.

Involvement of calpain in the process of Jurkat T cell chemotaxis

Massive T cell infiltration into the central nervous system is a hallmark of multiple sclerosis (MS) and its rodent model experimental autoimmune encephalomyelitis (EAE), resulting in the induction of many of the pathophysiological events that lead to neuroinflammation and neurodegeneration. Thus, blocking T cell migration into the central nervous system may reduce disease severity in MS and EAE. One potential target for reducing T cell migration is inhibition of the Ca(2+)-activated neutral protease calpain. Previous studies in other cell types have demonstrated that migration is reduced by incubation of cells with calpain inhibitors. Thus, we hypothesize that calpain inhibition will reduce migration of T cells in response to and toward the chemokine CCL2. To test this hypothesis, the intracellular free Ca(2+) levels in Jurkat E6-1 T cells was first measured by the fura-2 assay to assess whether the intracellular ion environment would support calpain activation. The intracellular free Ca(2+) levels were found to increase in response to CCL2. The cells were next treated with the calpain inhibitor calpeptin in a multiwelled Boyden chamber with CCL2 used as the chemoattractant. These studies demonstrate that inhibition of calpain with its inhibitor calpeptin produces a dose-dependent inhibition of chemotaxis. Calpain activity, as measured by live cell imaging, was also increased in response to CCL2, providing further evidence of its involvement in the process of chemotaxis and migration. These studies provide evidence for the involvement of calpain in the mechanisms of chemotaxis and warrants further exploration in MS patient and EAE animal samples.

MCP-1/CCR2 system is involved in high glucose-induced fibronectin and type IV collagen expression in cultured mesangial cells

Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that plays an important role in the recruitment of macrophages. Although previous studies have demonstrated the importance of MCP-1 in the pathogenesis of diabetic nephropathy (DN) in terms of inflammation, the role of MCP-1 and its receptor (C-C chemokine receptor 2; CCR2) in extracellular matrix (ECM) accumulation under diabetic conditions has been largely unexplored. This study was undertaken to investigate the functional role of the MCP-1/CCR2 system in high glucose-induced ECM (fibronectin and type IV collagen) protein expression in cultured mesangial cells (MCs). Mouse MCs were exposed to medium containing 5.6 mM glucose (NG), NG+24.4 mM mannitol (NG+M), or 30 mM glucose (HG) with or without mutant MCP-1 (mMCP-1), CCR2 small interfering (si)RNA, or CCR2 inhibitor (RS102895). To examine the relationship between MCP-1 and transforming growth factor (TGF)-β1, MCs were also treated with TGF-β1 (2 ng/ml) with or without mMCP-1 or CCR2 siRNA. Transient transfection was performed with Lipofectamine 2000 for 24 h. Cell viability was determined by an MTT assay, mouse and human MCP-1 and TGF-β1 levels by ELISA, and CCR2 and ECM protein expression by Western blotting. Transfections of mMCP-1 and CCR2 siRNA increased human MCP-1 levels and inhibited CCR2 expression, respectively. HG-induced ECM protein expression and TGF-β1 levels were significantly attenuated by mMCP-1, CCR2 siRNA, and RS102895 ( P < 0.05). MCP-1 directly increased ECM protein expression, and this increase was inhibited by an anti-TGF-β1 antibody. In addition, TGF-β1-induced ECM protein expression was significantly abrogated by the inhibition of the MCP-1/CCR2 system ( P < 0.05). These results suggest that an interaction between the MCP-1/CCR2 system and TGF-β1 may contribute to ECM accumulation in DN.

Circulating MCP-1 levels shows linkage to chemokine receptor gene cluster on chromosome 3: the NHLBI family heart study follow-up examination

Atherogenesis is a chronic inflammatory process. Critical in the inflammation process is monocyte chemoattractant protein-1 (MCP-1). To locate genomic regions that affect circulating MCP-1 levels, a genome-wide linkage scan was conducted in a sample of whites and blacks. Phenotype and genetic marker data were available for 2501 white and 513 black participants in the National Heart Lung Blood Institute Family Heart Study follow-up examination. Heritability for MCP-1 was 0.37 in whites and 0.47 in blacks after adjusting for the effects of sex, age, age-sex interaction, smoking status, lifetime smoking exposure (pack-years) and field center. Significant linkage was observed for MCP-1 in a combined black and white sample on chromosome 3 (logarithm of the odds ratio (LOD)=3.5 at 78 cM, P=0.0001) and suggestive linkage was observed in whites on chromosome 5 (LOD=1.8 at 128 cM, P=0.002). Located under the linkage peak on chromosome 3 is the chemokine receptor gene cluster, including CCR2, the receptor for MCP-1. This study provides preliminary evidence linking genetic variation in a receptor to circulating levels of its ligand, as previously demonstrated for the low-density lipoprotein receptor. Further characterization of these chromosomal regions is needed to identify the functional mutations associated with circulating levels of MCP-1.

CC chemokine receptor-2A is frequently overexpressed in glioblastoma

Macrophages and monocytes migrate in response to chemotactic cytokines such as monocyte chemoattractant protein 1 (MCP-1/CCL2) in a variety of tissues including the central nervous system. Overexpression of MCP-1 has been reported in glioblastoma (GBM), which correlates to prominent macrophage infiltration characterized by this tumor type, but whether MCP-1 receptor is also expressed by the neoplastic cells remains unclear. Expression of MCP-1 and its receptor, CC chemokine receptor 2 (CCR2), were examined in GBM using cDNA microarrays and validated in two independent microarray datasets. We investigated the expression of the CCR2A isoform in human glioma cell lines and GBM, and found overexpression of CCR2A in most GBM specimens examined when compared to normal brain tissues. CCR2A is mainly localized in the cytoplasm of neoplastic cells, and pronounced neuronal cytoplasmic CCR2A immunoreactivity in tumor-infiltrating area was associated with prior chemo/radiation therapy. Glioma cells ectopically overexpressing CCR2A demonstrated increased migration compared to vector-transfected cells in vitro. Inhibition of MCP-1 synthesis suppressed migration of CCR2A-overexpressed glioma cells. Our data suggest that CCR2A might be associated with the pathobiology of GBM such as host response to treatment and tumor cell migration.

Association of CCR2 polymorphisms with the number of closed coronary artery vessels in coronary artery disease

Coronary artery disease (CAD) is one of the most common forms of heart disease. It has been demonstrated that chemokine-mediated inflammation is associated with the development of CAD. In this study, in order to determine the role of CCR2, a receptor for MCP-1, in the development of CAD, we initially sequenced and identified the genetic variants of CCR2 using 24 unrelated Korean individuals' DNA samples. A total of 13 genetic variants, including 1 deletion and 12 SNPs, were identified in the Korean population. Although we could not detect any association of CCR2 polymorphic markers with CAD, several SNP markers of CCR2 gene showed highly significant signals with the number of arteries with significant coronary artery stenosis in the CAD male patients. The most significant signal was detected at the SNP located at exon 2 (+780T>C, Asn260Asn) CI: 1.19-1.87, P=0.0005 (odds ratio: 1.49, 95% CI: 1.19-1.87, p=0.0005) (Table 3). This result indicates that CCR2 can play a role in the pathogenesis of CAD, especially to the number of vessels in CAD.

Induction of chemokines and chemokine receptors CCR2b and CCR4 in authentic human osteoclasts differentiated with RANKL and osteoclast like cells differentiated by MCP-1 and RANTES

Chemokines MCP-1 and RANTES are induced when authentic bone resorbing human osteoclasts differentiate from monocyte precursors in vitro. In addition, MCP-1 and RANTES can stimulate the differentiation of cells with the visual appearance of osteoclasts, being multinuclear and positive for tartrate resistance acid phosphatase (TRAP +). We show here that MIP1alpha is also potently induced by RANKL during human osteoclast differentiation and that this chemokine also induces the formation of TRAP + multinucleated cells in the absence of RANKL. MIP1alpha was able to overcome the potent inhibition of GM-CSF on osteoclast differentiation, permitting the cells to pass through to TRAP + multinuclear cells, however these were unable to form resorption pits. Chemokine receptors CCR2b and CCR4 were potently induced by RANKL (12.6- and 49-fold, P = 4.0 x 10(-7) and 4.0 x 10(-8), respectively), while CCR1 and CCR5 were not regulated. Chemokine treatment in the absence of RANKL also induced MCP-1, RANTES and MIP1alpha. Unexpectedly, treatment with MCP-1 in the absence of RANKL resulted in 458-fold induction of CCR4 (P = 1.0 x 10(-10)), while RANTES treatment resulted in twofold repression (P = 1.0 x 10(-4)). Since CCR2b and CCR4 are MCP-1 receptors, these data support the existence of an MCP-1 autocrine loop in human osteoclasts differentiated using RANKL.

Protective role of the polymorphism CCR2-64I in the progression from squamous intraepithelial lesions to invasive cervical carcinoma

OBJECTIVE

Invasive cervical cancer (ICC) is one of the most common malignant diseases among women, representing almost 10% of all the cancers in the female population. The aim of this study was to explore the association of the CCR2-64I polymorphism with the risk of developing invasive cervical cancer (ICC) from squamous intraepithelial lesions (SILs).

METHODS

DNA samples were extracted from peripheral blood cells of 109 patients with squamous intraepithelial lesions (28 low-grade and 81 high-grade cases) and 217 patients with ICC. The CCR2-64I polymorphism was analyzed through polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) (BseJI). The odds ratio (OR) and its 95% confidence interval (CI) were calculated as a measure of the association between CCR2-64I genotypes and cervical cancer risk.

RESULTS

The frequency of the G/A genotype was significantly higher in SIL patients (n = 109) than ICC patients (n = 217) (P = 0.005; OR = 0.42; 95% CI: 0.22-0.83). Furthermore, no association was found when we analyzed the influence of the A allele in the progression from low-grade SIL (LSIL) to high-grade SIL (HSIL) (OR = 1.05; 95% CI = 0.370-2.98; P = 0.930), but a statistically significant association was found in the progression from high-grade SIL to ICC (OR = 0.435; 95% CI = 0.222-0.854; P = 0.014).

CONCLUSION

These findings suggest that CCR2-64I polymorphism might have a protective role in the evolution from high-grade SIL to ICC.

Synergy between proinflammatory ligands of G protein-coupled receptors in neutrophil activation and migration

The chemokine dose and the time period during which the chemotactic gradient is established determine the number of leukocytes that infiltrate inflamed tissues. At suboptimal chemokine concentrations, neutrophils may require a priming agent or a second stimulus for full activation. An interesting mode of cooperative action to reach maximal migration is synergy between chemokines. This was first observed between the plasma CC chemokine regakine-1 and the tissue CXC chemokine ligand interleukin-8 (IL-8/CXCL8) in neutrophil chemotaxis. Addition of antibodies against IL-8 or regakine-1 in the Boyden microchamber assay abrogated this synergy. Other CC chemokines, such as CC chemokine ligand-2 monocyte chemotactic protein-1 (MCP-1/CCL2), MCP-2 (CCL8), and MCP-3 (CCL7) as well as the CXC chemokine receptor-4 (CXCR4) agonist stromal cell-derived factor-1alpha (SDF-1alpha/CXCL12), also dose-dependently enhanced neutrophil chemotaxis toward a suboptimal concentration of IL-8. These chemokines synergized equally well with the anaphylatoxin C5a in neutrophil chemotaxis. Alternatively, IL-8 and C5a did not synergize with an inactive precursor form of CXCL7, connective tissue-activating peptide-III/CXCL7, or the chemoattractant neutrophil-activating peptide-2/CXCL7. In the chemotaxis assay under agarose, MCP-3 dose-dependently increased the migration distance of neutrophils toward IL-8. In addition, the combination of IL-8 and MCP-3 resulted in enhanced neutrophil shape change. AMD3100, a specific CXCR4 inhibitor, reduced the synergistic effect between SDF-1alpha and IL-8 significantly. SDF-1alpha, but not MCP-1, synergized with IL-8 in chemotaxis with CXCR1-transfected, CXCR4-positive Jurkat cells. Thus, proinflammatory chemokines (IL-8, MCP-1), coinduced during infection in the tissue, synergize with each other or with constitutive chemokines (regakine-1, SDF-1alpha) to enhance the inflammatory response.

Chemotaxis Receptors and Signaling

Chemotaxis is an important cellular response common in biology. In many chemotaxing cells the signal that regulates movement is initiated by G protein-coupled receptors on the cell surface that bind specific chemoattractants. These receptors share important structural similarities with other G protein-coupled receptors, including rhodopsin, which currently serves as the best starting point for modeling their structures. However, the chemotaxis receptors also share a number of relatively unique structural features that are less common in other GPCRs. The chemoattractant ligands of chemotaxis receptors exhibit a broad variety of sizes and chemical properties, ranging from small molecules and peptides to protein ligands. As a result, different chemotaxis receptors have evolved specialized mechanisms for the early steps of ligand binding and receptor activation. The mechanism of transmembrane signaling is currently under intensive study and several alternate mechanisms proposing different conformational rearrangements of the transmembrane helices have been proposed. Some chemotaxis receptors are proposed to form dimers, and in certain cases dimer formation is proposed to play a role in transmembrane signaling. In principle the structural and dynamical changes that occur during transmembrane signaling could be specialized for different receptors, or could be broadly conserved. Extensive mutagenesis studies have been carried out, and have begun to identify critical residues involved in ligand binding, receptor activation, and transmembrane signaling.

The Peyer's patch microenvironment suppresses T cell responses to chemokines and other stimuli

Immunosurveillance of mucosal sites presents immune cells with challenges not encountered in the periphery. T cells in the gut must distinguish enteric pathogens from innocuous non-self Ag derived from food or commensal bacteria. The mechanisms that regulate T cells in the gut remain incompletely understood. We assessed the effect of the Peyer's patch microenvironment on T cell responses to chemokines. Chemokines are believed to play an important role during T cell priming by facilitating T cell migration into and within lymphoid tissues as well as T cell encounter and interaction with APCs. We found a profound suppression of chemokine-stimulated T cell chemotaxis and actin polymerization in Peyer's patch relative to lymph node. Chemokine hyporesponsiveness is imposed upon T cells within hours of their entry into Peyer's patches and is reversed following their removal. Suppression was not restricted to chemokine stimulation, as T cell responses to Con A and PMA were also suppressed. The global nature of this defect is further underscored by an impairment in calcium mobilization. Evidence indicates that a soluble factor contributes to this hyporesponsiveness, and comparison of Peyer's patches and lymph nodes revealed striking differences in their chemokine and cytokine constitution, indicating a marked Th2 bias in the Peyer's patches. The role of the Th2 microenvironment in mediating suppression is suggested by the ability of Nippostrongylus brasiliensis to elicit hyporesponsiveness in lymph node T cells. The suppressive milieu encountered by T cells in Peyer's patches may be critical for discouraging undesired immune responses and promoting tolerance.