A selective and potent CXCR3 antagonist SCH 546738 attenuates the development of autoimmune diseases and delays graft rejection

ABSTRACT: BACKGROUND: The CXCR3 receptor and its three interferon-inducible ligands (CXCL9, CXCL10 and CXCL11) have been implicated as playing a central role in directing a Th1 inflammatory response. Recent studies strongly support that the CXCR3 receptor is a very attractive therapeutic target for treating autoimmune diseases, such as rheumatoid arthritis, multiple sclerosis and psoriasis, and to prevent transplant rejection. We describe here the in vitro and in vivo pharmacological characterizations of a novel and potent small molecule CXCR3 antagonist, SCH 546738. RESULTS: In this study, we evaluated in vitro pharmacological properties of SCH 546738 by radioligand receptor binding and human activated T cell chemotaxis assays. In vivo efficacy of SCH 546738 was determined by mouse collagen-induced arthritis, rat and mouse experimental autoimmune encephalomyelitis, and rat cardiac transplantation models. We show that SCH 546738 binds to human CXCR3 with a high affinity of 0.4 nM. In addition, SCH 546738 displaces radiolabeled CXCL10 and CXCL11 from human CXCR3 with IC50 ranging from 0.8 to 2.2 nM in a non-competitive manner. SCH 546738 potently and specifically inhibits CXCR3-mediated chemotaxis in human activated T cells with IC90 about 10 nM. SCH 546738 attenuates the disease development in mouse collagen-induced arthritis model. SCH 546738 also significantly reduces disease severity in rat and mouse experimental autoimmune encephalomyelitis models. Furthermore, SCH 546738 alone achieves dose-dependent prolongation of rat cardiac allograft survival. Most significantly, SCH 546738 in combination with CsA supports permanent engraftment. CONCLUSIONS: SCH 546738 is a novel, potent and non-competitive small molecule CXCR3 antagonist. It is efficacious in multiple preclinical disease models. These results demonstrate that therapy with CXCR3 antagonists may serve as a new strategy for treatment of autoimmune diseases, including rheumatoid arthritis and multiple sclerosis, and to prevent transplant rejection.     

CXCL4-induced migration of activated T lymphocytes is mediated by the chemokine receptor CXCR3

The chemokine CXCL4/platelet factor-4 is released by activated platelets in micromolar concentrations and is a chemoattractant for leukocytes via an unidentified receptor. Recently, a variant of the human chemokine receptor CXCR3 (CXCR3-B) was described, which transduced apoptotic but not chemotactic signals in microvascular endothelial cells following exposure to high concentrations of CXCL4. Here, we show that CXCL4 can induce intracellular calcium release and the migration of activated human T lymphocytes. CXCL4-induced chemotaxis of T lymphocytes was inhibited by a CXCR3 antagonist and pretreatment of cells with pertussis toxin (PTX), suggestive of CXCR3-mediated G-protein signaling via Galphai-sensitive subunits. Specific binding by T lymphocytes of the CXCR3 ligand CXCL10 was not effectively competed by CXCL4, suggesting that the two are allotopic ligands. We subsequently used expression systems to dissect the potential roles of each CXCR3 isoform in mediating CXCL4 function. Transient expression of the CXCR3-A and CXCR3-B isoforms in the murine pre-B cell L1.2 produced cells that migrated in response to CXCL4 in a manner sensitive to PTX and a CXCR3 antagonist. Binding of radiolabeled CXCL4 to L1.2 CXCR3 transfectants was of low affinity and appeared to be mediated chiefly by glycosaminoglycans (GAGs), as no specific CXCL4 binding was observed in GAG-deficient 745-Chinese hamster ovary cells stably expressing CXCR3. We suggest that following platelet activation, the CXCR3/CXCL4 axis may play a role in T lymphocyte recruitment and the subsequent amplification of inflammation observed in diseases such as atherosclerosis. In such a setting, antagonism of the CXCR3/CXCL4 axis may represent a useful, therapeutic intervention.     

Opposing roles for CXCR3 signaling in central nervous system versus ocular inflammation mediated by the astrocyte-targeted production of IL-12

CXCR3 and its ligands are important for the trafficking of activated CD4(+) T(H)1 T cells, CD8(+) T cells, and natural killer cells during inflammation. Recent functional studies demonstrate a more diverse role of CXCR3 in inflammatory diseases of the central nervous system (CNS). We examined the impact of CXCR3 on a less complex interferon-γ-dependent, type 1 cell-mediated immune response in the CNS, induced in mice by the transgenic production of glial fibrillary acidic protein IL-12 (GF-IL12) by astrocytes and retinal Müller cells. GF-IL12 mice develop ataxia because of severe cerebellar inflammation but have little overt ocular disease. Surprisingly, CXCR3-deficient GF-IL12 mice (GF-IL12/CXCR3KO) have drastically reduced ataxia but developed cataracts, severe ocular inflammation, and eye atrophy. Most GF-IL12/CXCR3KO mice had minimal cerebellar inflammation but severe retinal disorganization, loss of photoreceptors, and lens destruction in the eye. The number of CD3(+), CD11b(+), and natural killer 1.1(+) cells were reduced in the CNS but highly increased in the eyes of GF-IL12/CXCR3KO compared with GF-IL12 mice. High levels of interferon-γ, IL-1, tumor necrosis factor α, CXCL9, CXCL10, and CCL5 were found in GF-IL12 cerebelli and GF-IL12/CXCR3KO eyes. Our findings demonstrate key but paradoxical functions for CXCR3 in IL-12-induced immune disease in the CNS, promoting inflammation in the brain yet restricting it in the eye. We conclude that the function of CXCR3 in cellular immune disease is driven by a common trigger and is controlled by tissue-specific factors.     

Expression of rat I-TAC/CXCL11/SCYA11 during central nervous system inflammation: comparison with other CXCR3 ligands

The chemokines are a large gene superfamily with critical roles in development and immunity. The chemokine receptor CXCR3 appears to play a major role in the trafficking of activated Th1 lymphocytes. There are at least three major ligands for CXCR3: mig/CXCL9, IP-10/CXCL10 and I-TAC/CXCL11, and of these three ligands, CXCL11 is the least well-characterized. In this study, we have cloned a rat ortholog of CXCL11, evaluated its function, and examined its expression in the Th-1-mediated disease, experimental autoimmune encephalomyelitis (EAE) in the rat. Based on its predicted primary amino-acid sequence, rat I-TAC/CXCL11 was synthesized and shown to induce chemotaxis of activated rat T lymphocytes in vitro and the in vivo migration of T lymphocytes when injected into the skin. I-TAC/CXCL11 expression, as determined by RT-PCR, increased in lymph node and spinal cord tissue collected from rats in which EAE had been actively induced, and in spinal cord tissue from rats in which EAE had been passively induced. The kinetics of expression were similar to that of CXCR3 and IP-10/CXCL10, although expression of both CXCR3 and IP-10/CXCL10 was more intense than that of I-TAC/CXCL11 and increased more rapidly in both lymph nodes and the spinal cord. Only minor levels of expression of the related chemokine mig/CXCL9 were observed. Immunohistochemistry revealed that the major cellular source of I-TAC/CXCL11 in the central nervous system (CNS) during EAE is likely to be the astrocyte. Together, these data indicate that I-TAC/CXCL11 is expressed in the CNS during the clinical phase of EAE. However, the observation that I-TAC/CXCL11 is expressed after receptor expression is detected suggests that it is not essential for the initial migration of CXCR3-bearing cells into the CNS.     

Reciprocal regulation of CXCR4 and CXCR7 in intestinal mucosal homeostasis and inflammatory bowel disease

IBDs are characterized by increased influx of immune cells to the mucosa of genetically susceptible persons. Cellular migration to injury sites is mediated by chemokines. CXCL12 is a ubiquitous, constitutive chemokine that participates in stem cell proliferation and migration and mediates T lymphocyte migration to inflamed tissues. We have recently reported that CXCL12 and its receptor, CXCR4, are expressed in normal and more prominently, inflamed human intestinal mucosa. However, the interactions and roles of CXCL12 and its receptors, CXCR4 and the recently discovered CXCR7, in intestinal inflammation have not been defined. In the present study, we further dissected the effects of CXCL12 on lymphocytes in intestinal homeostasis and inflammation and delineated the interplay between CXCL12 and its receptors CXCR4 and CXCR7. To that end, fresh mononuclear cells were isolated from mucosa and PB of healthy or IBD patients. Phenotypical and functional assays were conducted using flow cytometry, Transwell migration chambers, and ELISA. The data show that CXCL12-mediated migration of T cells is CXCR4- but not CXCR7-dependent. T cell activation reciprocally regulates CXCR7 and CXCR4 expression and migratory capacity. IBD PBTs expressed more CXCR7 than normal PBTs. Finally, T cells attracted by CXCL12 are mostly of a memory phenotype. In conclusion, the present study suggests that the interplay between CXCL12 and its receptors affects homeostasis and inflammation in the intestinal mucosa.     

AMD3100干预调节性T细胞迁移机制研究

CXCR4+细胞在CD4+CD25+Foxp3+调节性T细胞亚群中占有一定的比例。趋化因子CXCL12与细胞表面的特异性受体CXCR4相互作用,调节这些细胞的迁移和归巢等生理过程。AMD3100是一种人工合成的大环类拮抗剂,可特异性拮抗CXCR4。本研究采用磁珠亲和细胞分选术纯化BALB/c小鼠脾脏CD4+CD25+调节性T细胞,并采用transwell共培养系统,研究AMD3100对调节性T细胞迁移的影响。研究发现,AMD3100以剂量依赖性模式抑制CXCR4+CD4+CD25+T细胞从transwell培养系统的上室迁移至下室,采用中和抗体阻断CXCR4可观察到相似效应。当AMD3100终浓度为2.0μg/ml时,迁移到下室的CXCR4+细胞占总数的2.2%,显著低于磷酸盐缓冲液对照组(36.2%)(P<0.01)。此外,CD4+CD25+细胞24h迁移率也显著下降(AMD3100处理组和磷酸盐缓冲液对照组分别为3.1%和35.5%,P<0.01)。提示AMD3100可特异性抑制CXCR4+CD4+CD25+细胞迁移。由于CXCR4是CXCL12的特异性受体,这一效应提示AMD3100可削弱CXCL12的作用。此外,由于AMD3100处理后可使CD4+CD25+细胞24h迁移率下降,提示这种拮抗剂有可能短时间内削弱调节性T细胞的功能。     

Expression and agonist responsiveness of CXCR3 variants in human T lymphocytes

The chemokine receptor CXCR3 and its ligands CXCL9, CXCL10 and CXCL11 are involved in variety of inflammatory disorders including multiple sclerosis, rheumatoid arthritis, psoriasis and sarcoidosis. Two alternatively spliced variants of the human CXCR3-A receptor have been described, termed CXCR3-B and CXCR3-alt. Human CXCR3-B binds CXCL9, CXCL10, CXCL11 as well as an additional ligand CXCL4. In contrast, CXCR3-alt only binds CXCL11. We report that CXCL4 induces intracellular calcium mobilization as well as Akt and p44/p42 extracellular signal-regulated kinase phosphorylation, in activated human T lymphocytes. These responses have similar concentration dependence and time-courses to those induced by established CXCR3 agonists. Moreover, phosphorylation of Akt and p44/p42 is inhibited by pertussis toxin, suggesting coupling to Gα(i) protein. Surprisingly, and in contrast with the other CXCR3 agonists, stimulation of T lymphocytes with CXCL4 failed to elicit migratory responses and did not lead to loss of surface CXCR3 expression. Taken together, our findings show that, although CXCL4 is coupled to downstream biochemical machinery, its role in T cells is probably distinct from that of CXCR3-A agonists.     

The chemokines CCL5, CCL2 and CXCL12 play significant roles in the migration of Th1 cells into rheumatoid synovial tissue

As the T-cell population in the synovial tissue (ST) in rheumatoid arthritis (RA) is dominated by T helper (Th) 1 cells, this study was designed to examine whether there is a preferential migration of polarized T cells to ST, and to identify the chemokines responsible for the migration. This was done by developing 10 T-cell clones specific for an arbitrary antigen (mouse immunoglobulin G (IgG)) from the peripheral blood (PB) of a healthy donor sensitized to mouse IgG. The Th polarizations of the clones were determined by measuring secreted interferon-gamma and interleukin-4, following anti-CD3 stimulation. Migration to pools of RA ST cell-derived supernatants was analysed. Expression of the chemokine receptors CCR1, CCR2, CCR3, CCR4, CCR5, CCR6, CCR7, CCR8, CXCR3 and CXCR4 were analysed by flow cytometry. Th1 clones showed significantly higher migration to RA ST cell-derived supernatant compared with Th2 clones. Blocking of either of the chemokines, CCL5 or CCL2, strongly inhibited migration of the Th1 cells between 56 and 77%, while blocking of CXCL12 inhibited migration between 44 and 61%. Blocking of CXCL10 had only a minor inhibitory effect. Our results demonstrate a selective migration of Th1 cells to RA ST supernatant and that blocking either CCL5, CCL2 or CXCL12 significantly inhibits T-cell migration. This indicates that CCL5, CCL2 and CXCL12 play significant roles in attracting Th1 cells towards the RA ST, and may prove potent targets for obstructing T-cell migration to the synovium.     

趋化因子及其受体CXCL12/CXCR4在人前列腺癌转移机制中的作用

目的 探讨趋化因子及其受体CXCL12/CXCR4在人前列腺癌转移机制中的作用.方法 免疫组织化学技术分析CXCL12/CXCR4蛋白在18例前列腺癌组织中的表达;免疫细胞化学技术分析CXCL12/CXCR4蛋白在人前列腺癌细胞株PC3、DU145和LNCap中的表达;迁移、侵袭试验分析外源性CXCL12对PC3、DU145和LNCap体外侵袭能力的调节作用.结果 18例人前列腺癌组织中,17例不同强度表达CXCR4蛋白,1例阴性表达,同时除1例标本弱表达CXCL12蛋白外,其余不表达CXCL12蛋白.3种前列腺癌细胞株均表达CXCR4蛋白,不表达CXCL12蛋白.外源性CXCLl2可明显促进PC3、DU145及LNCap的体外迁移、侵袭,以抗CXCL12或CXCR4抗体预处理PC3、LNCap细胞可以拮抗CXCL12对它们的促迁移、侵袭作用.结论 人前列腺癌组织表达CXCR4蛋白,CXCL12/CXCR4信号通路可能参与前列腺癌的侵袭、转移.     

Slit-2/Robo-1 modulates the CXCL12/CXCR4-induced chemotaxis of T cells

Slit, which mediates its function by binding to the Roundabout (Robo) receptor, has been shown to regulate neuronal, dendritic, and leukocyte migration. However, the molecular mechanism by which the Slit/Robo complex inhibits the migration of cells is not well defined. Here, we showed that Slit-2 can inhibit the CXCL12-induced chemotaxis and transendothelial migration of T cells and monocytes. We observed that CXCR4 associates with Robo-1 and that Slit-2 treatment enhances this association with the Robo-1 receptor. Robo-1 is a single-pass transmembrane receptor whose intracellular region contains four conserved motifs designated as CC0, CC1, CC2, and CC3. Structural and functional analyses of Robo receptors revealed that interaction of the CC3 motif with the CXCR4 receptor may regulate the CXCL12-induced chemotaxis of T cells. We further characterized Slit-2-mediated inhibition of the CXCL12/CXCR4 chemotactic pathway and found that Slit-2 can block the CXCL12-induced activation of the Src and Lck kinases but not Lyn kinase. Although Slit-2 did not inhibit the CXCL12-induced activation of MAPKs, it did inhibit the Akt phosphorylation and Rac activation induced by this chemokine. Altogether, our studies indicate a novel mechanism by which the Slit/Robo complex may inhibit the CXCR4/CXCL12-mediated chemotaxis of T cells.     

CXCR3-mediated opposite effects of CXCL10 and CXCL4 on TH1 or TH2 cytokine production

BACKGROUND: Two variants of the CXCR3 receptor exist, one (CXCR3-A) reactive with CXCL9, CXCL10, and CXCL11 and the other (CXCR3-B) also reactive with CXCL4. Both variants are contemporarily expressed by human T cells. OBJECTIVE: We sought to investigate the in vitro effects of CXCL10 and CXCL4 on the production of TH1 or TH2 cytokines. METHODS: The cytokine profile of antigen-specific human CD4+ T-cell lines obtained in the absence or presence of CXCL10 or CXCL4 was evaluated by means of quantitative RT-PCR, flow cytometry, and ELISA. RESULTS: CXCL10 upregulated IFN-gamma and downregulated IL-4, IL-5, and IL-13 production, whereas CXCL4 downregulated IFN-gamma and upregulated TH2 cytokines. Similar effects were also observed on polyclonally activated pure naive CD4+ T cells. The opposite effects of CXCL10 and CXCL4 on TH1 and TH2 cytokine production were inhibited by an anti-CXCR3 antibody able to neutralize both CXCR3-A and CXCR3-B and were apparently related to the activation of distinct signal transduction pathways. Moreover, CXCL10 upregulated mRNA levels of T-box expressed in T cells and downregulated GATA-3 expression, whereas CXCL4 downregulated T-box expressed in T cells and upregulated GATA-3. Finally, CXCL4, but not CXCL10, induced direct activation of IL-5 and IL-13 promoters. CONCLUSION: CXCL10 and CXCL4 exert opposite effects on the production of human TH1 and TH2 cytokines, likely through their respective interaction with CXCR3-A or CXCR3-B and the consequent activation of different signal transduction pathways. This might represent an internal regulatory pathway of TH cell responses and might contribute to the modulation of chronic inflammatory reactions, including allergy.     

CXCR4 expression affects overall survival of HCC patients whereas CXCR7 expression does not

Hepatocellular carcinoma (HCC) is a heterogeneous disease with a poor prognosis and limited markers for predicting patient survival. Because chemokines and chemokine receptors play numerous and integral roles in HCC disease progression, the CXCR4–CXCL12–CXCR7 axis was studied in HCC patients. CXCR4 and CXCR7 expression was analyzed by immunohistochemistry in 86 HCC patients (training cohort) and validated in 42 unrelated HCC patients (validation cohort). CXCR4 levels were low in 22.1% of patients, intermediate in 30.2%, and high in 47.7%, whereas CXCR7 levels were low in 9.3% of patients, intermediate in 44.2% and high in 46.5% of the patients in the training cohort. When correlated to patient outcome, only CXCR4 affected overall survival (P=0.03). CXCR4–CXCL12–CXCR7 mRNA levels were examined in 33/86 patients. Interestingly, the common CXCR4–CXCR7 ligand CXCL12 was expressed at significantly lower levels in tumor tissues compared to adjacent normal liver (P=0.032). The expression and function of CXCR4 and CXCR7 was also analyzed in several human HCC cell lines. CXCR4 was expressed in Huh7, Hep3B, SNU398, SNU449 and SNU475 cells, whereas CXCR7 was expressed in HepG2, Huh7, SNU449 and SNU475 cells. Huh7, SNU449 and SNU475 cells migrated toward CXCL12, and this migration was inhibited by AMD3100/anti-CXCR4 and by CCX771/anti-CXCR7. Moreover, SNU449 and Huh7 cells exhibited matrix invasion in the presence of CXCL12 and CXCL11, a ligand exclusive to CXCR7. In conclusion, CXCR4 affects the prognosis of HCC patients but CXCR7 does not. Therefore, the CXCR4–CXCL12–CXCR7 axis plays a role in the interaction of HCC with the surrounding normal tissue and represents a suitable therapeutic target.     

CXCR3 blockade inhibits T-cell migration into the CNS during EAE and prevents development of adoptively transferred, but not actively induced, disease

Autoreactive T-cell infiltration into the CNS is critical in MS and EAE. The chemokine receptor CXCR3 and its ligands are implicated in MS and mouse EAE, but the contribution of CXCR3 to T-cell migration into the inflamed CNS remains controversial. During active disease in a rat EAE model, blood T-cell, spleen T-cell and T lymphoblast migration into the CNS was inhibited by a CXCR3 blocking mAb by, 30-70%, ～75% and 50-80%, respectively. However, CXCR3 blockade after active immunization did not inhibit EAE, did not alter total T-cell accumulation in the CNS and did not affect Treg accumulation or the presence of cells producing IFN-γ or IL-17. Conversely, CXCR3 blockade during EAE induced by adoptive transfer of myelin basic protein-activated T cells delayed disease onset, shortened its duration and reduced disease severity. Moreover, CXCR3 blockade inhibited leukocyte infiltration of the CNS>95%, virtually abolishing infiltration of transferred T cells. Thus, CXCR3 plays a major role in T-cell migration to the CNS and can be critical for encephalitogenic T-cell migration into the CNS to induce disease, but CXCR3-independent recruitment can also produce EAE.     

Differential roles for CXCR3 in CD4+ and CD8+ T cell trafficking following viral infection of the CNS

Lymphocyte infiltration into the central nervous system (CNS) following viral infection represents an important component of host defense and is required for control of viral replication. However, the mechanisms governing inflammation in response to viral infection of the CNS are not well understood. Following intracranial (i.c.) infection of susceptible mice with mouse hepatitis virus (MHV), mice develop an acute encephalomyelitis followed by a chronic demyelinating disease. The CXC chemokine ligand 10 (CXCL10) is expressed following MHV infection and signals T cells to migrate into the CNS. The functional contribution of the CXCL10 receptor CXCR3 in host defense and disease in response to MHV infection was evaluated. The majority of CD4+ and CD8+ T cells infiltrating the CNS following MHV infection express CXCR3. Administration of anti-CXCR3 antibody reduced CD4+ T cell infiltration (p相似文献   

CXCL12-CXCR4 interactions modulate prostate cancer cell migration, metalloproteinase expression and invasion

The mechanisms responsible for prostate cancer metastasis are incompletely understood at both the cellular and molecular levels. In this regard, chemokines are a family of small, cytokine-like proteins that induce motility of neoplastic cells, leukocytes and cancer cells. The current study evaluates the molecular mechanisms of CXCL12 and CXCR4 in prostate cancer cell migration and invasion. We report that functional CXCR4 is significantly expressed by prostate cancer cell lines, LNCaP and PC3, when compared with normal prostatic epithelial cells (PrEC). As measured using motility and invasion chamber assays, prostate cancer cells migrated and invaded through extracellular matrix components in response to CXCL12, at rates that corresponded to CXCR4 expression. Anti-CXCR4 antibodies (Abs) significantly impaired the migration and invasive potential of PC3 and LNCaP cells. CXCL12 induction also enhanced collagenase-1 (metalloproteinase-1 (MMP-1)) expression by LNCaP and PC3 cells. Collagenase-3 (MMP-13) was expressed by prostate cancer cells, but it was not expressed by PrEC cells or modulated by CXCL12. CXCL12 increased MMP-2 expression by LNCaP and PC3; however, MMP-9 expression was elevated only in PC3 cells after CXCL12-CXCR4 ligation. PC3 cells also expressed high levels of stromelysin-1 (MMP-3) after CXCL12 stimulation. CXCL12 also significantly increased stromelysin-2 (MMP-10) expression by LNCaP cells. Stromelysin-3 (MMP-11) was expressed by LNCaP cells, but not by PC3 or PrEC cells and CXCL12 induced PC3 MMP-11 expression. Membrane type-1 MMP (MMP-14) was not expressed by PrEC or LNCaP cells, but CXCL12 significantly enhanced MMP-14 expression by PC3 cells. These studies reveal important cellular and molecular mechanisms of CXCR4/CXCL12-mediated prostate cancer cell migration and invasion.     

Cannabinoid receptor CB2 modulates the CXCL12/CXCR4-mediated chemotaxis of T lymphocytes

Cannabinoids have been shown to influence the immune system. However, their immunomodulatory effects have not been extensively studied. In this investigation, we have observed that both primary and Jurkat T cells express a functional cannabinoid receptor 2 (CB₂). Furthermore, both the synthetic cannabinoids CP55,940 and WIN55,212-2, as well as the CB₂-selective agonist JWH-015, caused a significant inhibition of the chemokine CXCL12-induced and CXCR4-mediated chemotaxis of Jurkat T cells, as well as their transendothelial migration. Involvement of the CB₂ receptor was further confirmed by partial reversal of the inhibition using the CB₂-specific antagonist, AM630. Similarly, CP55,940 and JWH-015 inhibited the CXCL12-induced chemotaxis of primary CD4⁺ and CD8⁺ T lymphocytes. Further investigation of signaling studies to delineate the mechanism of inhibition revealed that cannabinoids enhance CXCL12-induced p44/42 MAP kinase activity. However, enhanced MAP kinase activity was not responsible for the inhibition of chemotaxis. This suggests that cannabinoids differentially regulate CXCR4-mediated migration and MAP kinase activation in T cells. Cannabinoids were also found to downregulate the PMA-enhanced enzyme activity of matrix metalloproteinase-9, which is known to play an important role in transendothelial migration. This study provides novel information regarding cannabinoid modulation of functional effects in T cells.     

Critical involvement of atypical chemokine receptor CXCR7 in allergic airway inflammation

Trafficking and recruitment of immune cells to the site of inflammation with spatial and temporal synchronization is crucial for the development of allergic airway inflammation. Particularly, chemokines are known to be key players in these processes. Previous studies revealed that the CXCL12/CXCR4 axis plays an important role in regulating allergic airway inflammation. However, the role of CXCR7, a recently discovered second receptor for CXCL12, in regulating airway inflammation has not been explored. Initially, CXCR7 was considered as a decoy receptor; however, numerous subsequent studies revealed that engagement of CXCR7 triggered its own signalling or modulated CXCR4‐mediated signalling. In the present study, we detected the expression of CXCR7 in airway epithelial cells. Use of a lentiviral delivery system to knock down the expression of CXCR7 in the lung of sensitized mice abrogated the cardinal features of asthma, indicating that CXCR7 plays a role in regulating allergic airway inflammation. The activation of mitogen‐activated protein kinase and Akt signalling in response to CXCL12 in the mouse epithelial cell line MLE‐12 was reduced when CXCR7 expression was knocked down. However, either knockdown or overexpression of CXCR7 in MLE‐12 did not affect CXCL12‐mediated calcium influx, indicating that CXCR7 does not modulate CXCR4‐mediated signalling, and that it functions as a signalling receptor rather than a decoy receptor. Finally, we found that the expression of chemokine CCL2 is regulated by CXCR7/CXCL12‐mediated signalling through β‐arrestin in airway epithelial cells. Hence, regulating the expression of CCL2 in airway epithelial cells may be one mechanism by which CXCR7 participates in regulating allergic airway inflammation.     

A crosstalk between intracellular CXCR7 and CXCR4 involved in rapid CXCL12-triggered integrin activation but not in chemokine-triggered motility of human T lymphocytes and CD34+ cells

The chemokine CXCL12 promotes migration of human leukocytes, hematopoietic progenitors, and tumor cells. The binding of CXCL12 to its receptor CXCR4 triggers Gi protein signals for motility and integrin activation in many cell types. CXCR7 is a second, recently identified receptor for CXCL12, but its role as an intrinsic G-protein-coupled receptor (GPCR) has been debated. We report that CXCR7 fails to support on its own any CXCL12-triggered integrin activation or motility in human T lymphocytes or CD34(+) progenitors. CXCR7 is also scarcely expressed on the surface of both cell types and concentrates right underneath the plasma membrane with partial colocalization in early endosomes. Nevertheless, various specific CXCR7 blockers get access to this pool and attenuate the ability of CXCR4 to properly rearrange by surface-bound CXCL12, a critical step in the ability of the GPCR to trigger optimal CXCL12-mediated stimulation of integrin activation in T lymphocytes as well as in CD34(+) cells. In contrast, CXCL12-triggered CXCR4 signaling to early targets, such as Akt as well as CXCR4-mediated chemotaxis, is insensitive to identical CXCR7 blocking. Our findings suggest that although CXCR7 is not an intrinsic signaling receptor for CXCL12 on lymphocytes or CD34(+) cells, its blocking can be useful for therapeutic interference with CXCR4-mediated activation of integrins.     

The relative activity of CXCR3 and CCR5 ligands in T lymphocyte migration: concordant and disparate activities in vitro and in vivo

In chronic inflammatory reactions such as rheumatoid arthritis and multiple sclerosis, T cells in the inflamed tissue express the chemokine receptors CXCR3 and CCR5, and the chemokine ligands (CCL) of these receptors are present in the inflammatory lesions. However, the contribution of these chemokines to T cell recruitment to sites of inflammation is unclear. In addition, the relative roles of the chemokines that bind CXCR3 (CXCL9, CXCL10, CXCL11) and CCR5 (CCL3, CCL4, CCL5) in this process are unknown. The in vitro chemotaxis and in vivo migration of antigen-activated T lymphoblasts and unactivated spleen T cells to chemokines were examined. T lymphoblasts migrated in vitro to CXCR3 ligands with a relative potency of CXCL10 > CXCL11 > CXCL9, but these cells demonstrated much less chemotaxis to the CCR5 ligands. In vivo, T lymphocytes were recruited in large numbers with rapid kinetics to skin sites injected with CXCL10 and CCL5 and less to CCL3, CCL4, CXCL9, and CXCL11. The combination of CCL5 with CXCL10 but not the other chemokines markedly increased recruitment. Coinjection of interferon-gamma, tumor necrosis factor alpha, and interleukin-1alpha to up-regulate endothelial cell adhesion molecule expression with CXCL10 or CCL5 induced an additive increase in lymphoblast migration. Thus, CXCR3 ligands are more chemotactic than CCR5 ligands in vitro; however, in vivo, CXCL10 and CCL5 have comparable T cell-recruiting activities to cutaneous sites and are more potent than the other CXCR3 and CCR5 chemokines. Therefore, in vitro chemotaxis induced by these chemokines is not necessarily predictive of their in vivo lymphocyte-recruiting activity.