Chemokine stromal cell-derived factor 1alpha activates basophils by means of CXCR4

BACKGROUND: The CXC chemokine receptor 4 (CXCR4) is predominantly expressed on inactivated naive T lymphocytes, B lymphocytes, dendritic cells, and endothelial cells. CXC chemokine stromal cell-derived factor 1alpha (SDF-1alpha) is the only known ligand for CXCR4. To date, the CXCR4 expression and function of SDF-1alpha in basophils are unknown. OBJECTIVE: The purpose of this study was to investigate the expression of CXCR4 and functions of SDF-1alpha in basophils and to characterize the role of the CXCR4-SDF-1alpha receptor ligand pair in the allergic inflammation. METHODS: Basophil purification, flow cytometry, real-time quantitative RT-PCR assay, Northern blotting, intracellular free Ca(2+) change, chemotaxis assay, and histamine release assay were used. RESULTS: CXCR4 is abundantly expressed on peripheral blood resting basophils (91%). Likewise, CXCR4 messenger (m)RNA is expressed in resting basophils (3.2 x 10(3) copies per 2 x 10(2) cells). The existence of CXCR4 mRNA was also confirmed in basophils by means of Northern blot analysis. SDF-1alpha induces an increase in intracellular free Ca(2+) in basophils. SDF-1alpha activates basophils to chemotaxis (chemotactic index = 3.8) and histamine release (36% of total content) through CXCR4 on the cells. The chemokines SDF-1alpha, eotaxin, RANTES, monocyte chemoattractant protein (MCP) 1, and macrophage inflammatory protein (MIP) 1alpha have been demonstrated at different potencies in induction of chemotaxis (eotaxin > SDF-1alpha > RANTES congruent with MCP-1 > MIP-1alpha) and histamine release (MCP-1 congruent with SDF-1alpha > eotaxin > RANTES > MIP-1alpha). The optimal concentration seen for SDF-1alpha effects (chemotaxis and histamine release) on basophils was 100 ng/mL. CONCLUSION: These results indicate that the CXCR4-SDF-1alpha receptor ligand pair may be important for the recruitment and activation of the basophils, which is a characteristic effector cell of the allergic inflammation.     

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.     

SDF-1 induces IL-8 production and transendothelial migration of human cord blood-derived mast cells

BACKGROUND: Mast cell numbers and expression of chemokines are known to increase in the context of angiogenesis and inflammation, but the mechanisms by which this occurs are not understood. Stromal-derived factor-1 (SDF-1) is an important chemokine in angiogenesis and cell migration. The effects of SDF-1 on human mast cells were examined. METHODS: Expression of the SDF-1 receptor CXC chemokine receptor 4 (CXCR4) on mast cells was examined by RT-PCR and flow cytometry. The ability of labeled cord blood-derived mast cells to migrate across HUVEC monolayers in response to SDF-1 was determined. The cytokine and chemokine responses of cord blood-derived mast cells to SDF-1 treatment over 24 h were examined by ELISA. RESULTS: Cord blood-derived human mast cells expressed the CXCR4 receptor for SDF-1 and migrated across HUVEC monolayers in response to this chemokine. Treatment of cord blood-derived mast cells with SDF-1 did not induce degranulation or the production of several cytokines but did induce a highly selective IL-8 response. CONCLUSION: Human mast cells can both migrate across vascular endothelium and produce the pro-angiogenic chemokine IL-8 in response to SDF-1. These responses may be important in angiogenic processes.     

Vascular endothelial growth factor and basic fibroblast growth factor induce expression of CXCR4 on human endothelial cells: In vivo neovascularization induced by stromal-derived factor-1alpha

The contribution of chemokines toward angiogenesis is currently a focus of intensive investigation. Certain members of the CXC chemokine family can induce bovine capillary endothelial cell migration in vitro and corneal angiogenesis in vivo, and apparently act via binding to their receptors CXCR1 and CXCR2. We used an RNAse protection assay that permitted the simultaneous detection of mRNA for various CXC chemokine receptors in resting human umbilical vein endothelial cells (HUVECs) and detected low levels of only CXCR4 mRNA. Stimulation of HUVECs with vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF) up-regulated levels of only CXCR4 mRNA. CXCR4 specifically binds the chemokine stromal-derived factor-1alpha (SDF-1alpha). Competitive binding studies using 125I-labeled SDF-1alpha with Scatchard analysis indicated that VEGF or bFGF induced an average number of approximately 16,600 CXCR4 molecules per endothelial cell, with a Kd = 1.23 x 10(-9) mol/L. These receptors were functional as HUVECs and human aorta endothelial cells (HAECs) migrated toward SDF-1alpha. Although SDF-1alpha-induced chemotaxis was inhibited by the addition of a neutralizing monoclonal CXCR4 antibody, endothelial chemotaxis toward VEGF was not altered; therefore, the angiogenic effect of VEGF is independent of SDF-1alpha. Furthermore, subcutaneous SDF-1alpha injections into mice induced formation of local small blood vessels that was accompanied by leukocytic infiltrates. To test whether these effects were dependent on circulating leukocytes, we successfully obtained SDF-1alpha-induced neovascularization from cross sections of leukocyte-free rat aorta. Taken together, our data indicate that SDF-1alpha acts as a potent chemoattractant for endothelial cells of different origins bearing CXCR4 and is a participant in angiogenesis that is regulated at the receptor level by VEGF and bFGF.     

SDF-1/CXCR4生物学轴与肿瘤关系的研究进展

趋化因子SDF-1,又称CXCL12,PBSF,与其特异性受体CXCR4广泛表达在多种组织和器官上,它们所构成的SDF-1/CXCR4 生物学轴在多种肿瘤的发生,发展以及转移中都发挥重要作用,其可能是通过MAPK,AKT通路发挥作用。对这一特殊生物学轴的研究可能为肿瘤防治找到新的突破口。     

The role of HIV-related chemokine receptors and chemokines in human erythropoiesis in vitro

In order to better define the role of HIV-related chemokines in human erythropoiesis we studied: A) the expression of chemokine receptors, both on human CD34(+) cells which include erythroid progenitors and on more mature erythroid cells; B) the functionality of these receptors by calcium flux, chemotaxis assay and phosphorylation of mitogen-activated protein kinases (MAPK) p42/44 (ERK1/ERK2) and AKT, and finally C) the influence of chemokines on BFU-E formation. We found that HIV-related chemokine receptor CXCR4, but not CCR5, is detectable on human CD34(+) BFU-E cells. CXCR4 surface expression decreased during erythroid maturation, although CXCR4 mRNA was still present in cells isolated from differentiated erythroid colonies. SDF-1, a CXCR4 ligand, induced calcium flux and phosphorylation of MAPK (p42/44) and AKT in CD34(+)KIT(+) bone marrow mononuclear cells which contain BFU-E, as well as chemotactic activity of both human CD34(+) BFU-E progenitors and erythroid cells isolated from day 2-6 BFU-E colonies. Responsiveness to SDF-1 decreased when the cells differentiated to the point of surface expression of the erythroid-specific marker Glycophorin-A. In contrast, the CCR5 ligands (macrophage inflammatory protein-1alpha [MIP-1alpha], MIP-1beta, and RANTES) did not activate calcium flux, MAPK and AKT phosphorylation or chemotaxis of CD34(+)KIT(+) cells or cells isolated from the BFU-E colonies. Interestingly, none of the chemokines tested in this study had any effect on BFU-E colony formation. In conclusion, only CXCR4 is functional, and its specific ligand SDF-1 may therefore play an important role in the homing and/or retention of early erythroid precursors in the bone marrow environment.     

CXC chemokines and their receptors are expressed in type II cells and upregulated following lung injury

The proinflammatory CXC chemokines GRO, CINC-2alpha, and macrophage inflammatory protein (MIP)-2 are a closely related family of neutrophil chemoattractants. Here, we report that freshly isolated alveolar Type II (TII) cells express these chemokine mRNAs at much higher levels than do freshly isolated Type I cells or alveolar macrophages (AM). TII cells also express CXCR2, the receptor for these chemokines. Lung injury caused by acid or Pseudomonas aeruginosa (Pa) caused an increase in TII cell expression of chemokine mRNAs and GRO protein. We compared the time courses of chemokine mRNA expression in cultured TII cells and AM. In TII cells, GRO mRNA levels were stable over 4 h, but decreased to undetectable levels by 24 h. CINC-2alpha and MIP-2 mRNA levels were low in freshly isolated cells, increased over 2-4 h in culture, and by 24 h dropped to undetectable levels. In contrast, none of these chemokine mRNAs were detected in freshly isolated AM, but expression was induced by tissue culture. In summary, we have shown that TII alveolar epithelial cells produce three of the major proinflammatory CXC chemokines (GRO, CINC-2alpha, and MIP-2) and their cognate receptor CXCR2. Chemokine expression is upregulated in response to lung injury. These observations support a central role for the TII cell as an immunologic effector cell in the alveolus and raise intriguing questions about how CXC chemokines and receptors modulate diverse normal and pathologic cellular responses in the alveoli.     

Stromal-Cell Derived Factor Is Expressed by Dendritic Cells and Endothelium in Human Skin

Stromal-cell derived factor or SDF-1 is a CXC chemokine constitutively expressed by stromal bone marrow cell cultures that binds to the G-protein-coupled receptor CXCR4. SDF-1/CXCR4 represents a unique, nonpromiscuous ligand/receptor pair that plays an essential role in prenatal myelo- and lymphopoiesis as well as in cardiovascular and neural development. SDF-1 prevents entry of CXCR4-dependent (X4) HIV viruses in T lymphocytes, by binding and internalizing CXCR4. The expression pattern of SDF-1 protein in normal tissues is not known. Here we describe an analysis of SDF-1 mRNA and protein in normal and inflamed skin by in situ hybridization and immunohistochemistry, using a novel anti-SDF-1 monoclonal antibody. We also describe the expression pattern of CXCR4 receptor by immunohistochemistry. Our results show that SDF-1 protein and mRNA are normally expressed by endothelial cells, pericytes, and either resident or explanted CD1a+ dendritic cells. Epithelial cells of sweat glands but not keratinocytes also express SDF-1. In various inflammatory skin diseases, a large number of mononuclear cells and fibroblasts in close contact with CXCR4-positive lymphocytic infiltrates also express SDF-1. CXCR4 was also detected in many different normal cell types, including endothelial and epithelial cells, which points to a role for SDF-1/CXCR4 cell signaling in vascular and epithelial homeostasis. The demonstration of SDF-1 expression in dendritic and endothelial cells provides new insights into the mechanisms of normal and pathological lymphocyte circulation and makes it possible to envisage a role for locally secreted SDF-1 in the selective incapacity of mucosal dendritic cells to support and propagate infection by X4 HIV isolates.     

Endotoxin induces rapid metalloproteinase-mediated shedding followed by up-regulation of the monocyte hemoglobin scavenger receptor CD163

Several lines of evidence have suggested that a CXC chemokine receptor 4 (CXCR4)/stromal cell-derived factor-1 [SDF-1; CXC chemokine ligand 12 (CXCL12)] pair is involved in baseline trafficking of leukocytes into extravascular tissues and that modulation of surface CXCR4 expression may represent an alternative mechanism for control of cell-specific biological responses to SDF-1/CXCL12. We explored the regulation of CXCR4 expression by cytokines in polymorphonuclear neutrophils (PMNs). No significant surface expression of CXCR4 in freshly isolated PMNs was detected, but expression became apparent gradually during incubation. SDF-1alpha/CXCL12 initiated Ca2+ mobilization and migratory responses in 20 h cultured PMNs. The surface CXCR4 expression was suppressed most potently by interferon-gamma (IFN-gamma). IFN-alpha, granulocyte-macrophage colony-stimulating factor (GM-CSF), and G-CSF also inhibited spontaneous CXCR4 expression. Real-time, quantitative PCR experiments revealed that a spontaneous increase and an IFN-gamma-mediated decrease in surface CXCR4 paralleled changes in the CXCR4 mRNA level. These results on PMNs support the argument that the SDF-1 (CXCL12)/CXCR4 system is regulated by cell type-specific mechanisms.     

移植物抗宿主病小鼠肝脏及异体CD8+ T细胞趋化因子和趋化因子受体表达分析

为探讨趋化因子及其受体介导的效应性细胞迁移在移植物抗宿主病(graft-versus-host disease,GVHD)发生发展中的重要作用,采用次要组织相容性抗原异配的GVHD小鼠模型,应用流式细胞分选术(FACS)、实时荧光定量聚合酶链反应等方法,分析GVHD靶器官和异体CD8+T细胞趋化因子及受体的表达。肝脏高表达干扰素诱导蛋白-10(IP-10)、干扰素诱导的T细胞趋化因子(ITAC)、γ干扰素诱生单核因子(MIG)、巨噬细胞炎症蛋白(MIP)-1α/β等趋化因子。异体CD8+T细胞上则高表达CXC趋化因子受体(CXCR)3和CC趋化因子受体(CCR)5。随着肝脏趋化因子的表达增加,异体CD8+T细胞迁移浸润的数量也增高。因而趋化因子及异体CD8+T细胞上趋化因子受体的特异对应关系,促使大量异体CD8+T细胞迁移浸润并造成肝脏损伤。     

Maturation decreases responsiveness of human bone marrow B lineage cells to stromal-derived factor 1 (SDF-1).

We compared the chemotactic responsiveness of different subsets of human B lineage cells to stromal derived factor-1 (SDF-1). High percentages (30-40% of input) of purified bone marrow progenitors including non-B lineage progenitors, pro-B cells, and pre-B cells migrated to SDF-1alpha, demonstrating that SDF-1 is an efficacious chemoattractant of these cells. Pro-B cells responded optimally to a lower concentration of SDF-1 than other subsets, demonstrating that SDF-1 is a more potent chemoattractant of this subset. A lower percentage (10-15% of input) of mature B lymphocytes migrated to SDF-1alpha than pro-B cells, demonstrating that responsiveness of B lineage cells to SDF-1 decreases during differentiation. Inhibition by anti-CXCR4 mAb demonstrated that migration of B lineage cells to SDF-1 was completely dependent on CXC chemokine receptor-4 (CXCR4). Mature B cells expressed higher levels of CXCR4 receptors than uncommitted progenitors and pro-B cells, despite differences in responsiveness to SDF-1. CXCR4 receptors expressed by unresponsive and SDF-1-responsive B cells bound SDF-1alpha with similar affinities (K(D) = 1.7-3.3 x 10(-9) M). Therefore, elements downstream from CXCR4 appear to regulate responsiveness of B cells to SDF-1. We speculate that SDF-1 and CXCR4 direct migration of progenitor cells in microenvironments that promote B lymphopoiesis.     

The chemokine SDF-1α triggers a chemotactic response and induces cell polarization in human B lymphocytes

We studied the expression and possible functional role of chemokine receptors CXCR3, CXCR4 and CCR5 in normal human B lymphocytes. B cells from both peripheral blood and tonsils expressed high levels of CXCR4 but not the other chemokine receptors tested. CXCR4 ligand, stromal cell-derived factor (SDF)-1α, elicited a potent chemotactic response and induced a polarized motile phenotype in B cells, resulting in redistribution of the adhesion molecule ICAM-3 to a posterior appendage of the cell, termed uropod, and of CXCR4 receptor to the leading edge of migrating B cells. Time-lapse videomicroscopy studies revealed that SDF-1α-treated cells recruited additional bystander B cells through the uropod. SDF-1α induced levels of cellular recruitment comparable to those elicited by polarization-inducing anti-ICAM-3 monoclonal antibody, in an LFA-1/ICAM-1, −3-dependent fashion. Moreover, this chemokine increased intracellular Ca²⁺ levels in B lymphocytes, and induced a rapid CXCR4 receptor down-regulation on the cell surface membrane. These results provide new insight into the important biological role of SDF-1α in physiological processes in which B cells participate, and suggest a key role for chemokines in normal B cell trafficking and recirculation.     

The in vitro migration capacity of human bone marrow mesenchymal stem cells: comparison of chemokine and growth factor chemotactic activities

Adult bone marrow (BM)-derived stem cells, including hematopoietic stem cells (HSCs) and MSCs, represent an important source of cells for the repair of a number of damaged tissues. In contrast to HSCs, the soluble factors able to induce MSC migration have not been extensively studied. In the present work, we compared the in vitro migration capacity of human BM-derived MSCs, preincubated or not with the inflammatory cytokines interleukin 1beta (IL1beta) and tumor necrosis factor alpha (TNFalpha), in response to 16 growth factors (GFs) and chemokines. We show that BM MSCs migrate in response to many chemotactic factors. The GFs platelet-derived growth factor-AB (PDGF-AB) and insulin-like growth factor 1 (IGF-1) are the most potent, whereas the chemokines RANTES, macrophage-derived chemokine (MDC), and stromal-derived factor-1 (SDF-1) have limited effect. Remarkably, preincubation with TNFalpha leads to increased MSC migration toward chemokines, whereas migration toward most GFs is unchanged. Consistent with these results, BM MSCs express the tyrosine kinase receptors PDGF-receptor (R) alpha, PDGF-Rbeta, and IGF-R, as well as the RANTES and MDC receptors CCR2, CCR3, and CCR4 and the SDF-1 receptor CXCR4. TNFalpha increases CCR2, CCR3, and CCR4 expression (as opposed to that of CXCR4), together with RANTES membrane binding. These data indicate that the migration capacity of BM MSCs is under the control of a large range of receptor tyrosine kinase GFs and CC and CXC chemokines. Most chemokines are more effective on TNFalpha-primed cells. Our results suggest that the mobilization of MSCs and their subsequent homing to injured tissues may depend on the systemic and local inflammatory state. Disclosure of potential conflicts of interest is found at the end of this article.     

Loss of SDF-1 receptor expression during positive selection in the thymus

SDF-1 is a member of the CXC chemokines. In contrast to other chemokines that are induced by inflammation, SDF-1 is constitutively produced by stromal cells. In order to investigate the physiological roles of SDF-1, we constructed a fusion protein, SDF-1-Cgamma1, composed from murine SDF-1alpha and the constant region of human IgG. SDF-1-Cgamma1 stained EL-4 T lymphoma cells and the staining was blocked by rhSDF-1beta. The expression levels of SDF-1R altered along with the T cell maturation. Most c-kit+ hematopoietic precursors in fetal liver in gestational day (GD) 14.5 embryo were SDF-1R-, while c- kit+ double-negative (DN) thymocytes in the embryo were positive for SDF-1R. The receptor expression increased along with T cell maturation up to double-positive (DP) cell stage. Interestingly, SDF-1R expression was down-modulated after positive selection; CD69+CD3hi DP and CD3hi single-positive thymocytes were SDF-1R-/lo. Northern blot analysis demonstrated that SDF-1 and CXCR4 mRNAs were abundantly expressed in the thymuses of embryo and adult mice. These results demonstrate that SDF-1R expression is involved in T cell development in the thymus, particularly in positive selection.      

Allo-immunization elicits CCR5 antibodies,SDF-1 chemokines,and CD8-suppressor factors that inhibit transmission of R5 and X4 HIV-1 in women

Studies in humans suggest that allo-immunization induces CC-chemokines, CD8-suppressor factors (SF) and anti-HIV immunity. Here we report that allo-immunization with unmatched leucocytes from partners of women with recurrent spontaneous abortion elicits specific antibodies to the CCR5 receptor. Such antibodies inhibit replication of M-tropic HIV-1 (R5) and MIP-1beta-mediated chemotaxis. These CCR5 antibodies were also found in the sera of multiparous women that were naturally immunized by semi-allogeneic fetal antigens. The specificity of these antibodies was demonstrated by adsorption with CCR5 transfected HEK-293 cells, a baculovirus CCR5 preparation and a peptide of the 2nd extra-cellular loop of CCR5. Allo-immunization also stimulated increased concentrations of the CXC chemokine, SDF-1alpha and CD8-SF that inhibit T-tropic HIV-1 (X4) replication. We suggest that allo- immunization may elicit (a) CC chemokines, CCR5 antibodies and CD8-SF that inhibit M-tropic HIV-1 infection and (b) the CXC chemokine SDF-1alpha and CD8-SF that inhibit T-tropic HIV-1 infection.     

I-TAC/CXCL11 is a natural antagonist for CCR5

The selective CXC chemokine receptor 3 (CXCR3) agonists, monokine induced by interferon-gamma (IFN- gamma)/CXC chemokine ligand 9 (CXCL9), IFN-inducible protein 10/CXCL10, and IFN-inducible T cell alpha chemoattractant (I-TAC)/CXCL11, attract CXCR3+ cells such as CD45RO+ T lymphocytes, B cells, and natural killer cells. Further, all three chemokines are potent, natural antagonists for chemokine receptor 3 (CCR3) and feature defensin-like, antimicrobial activities. In this study, we show that I-TAC, in addition to these effects, acts as an antagonist for CCR5. I-TAC inhibited the binding of macrophage-inflammatory protein-1alpha (MIP-1alpha)/CC chemokine ligand 3 (CCL3) to cells transfected with CCR5 and to monocytes. Furthermore, cell migration evoked by regulated on activation, normal T expressed and secreted (RANTES)/CCL5 and MIP-1beta/CCL4, the selective agonist of CCR5, was inhibited in transfected cells and monocytes, respectively. In two other functional assays, namely the release of free intracellular calcium and actin polymerization, I-TAC reduced CCR5 activities to minimal levels. Sequence and structure analyses indicate a potential role for K17, K49, and Q51 of I-TAC in CCR5 binding. Our results expand on the potential role of I-TAC as a negative modulator in leukocyte migration and activation, as I-TAC would specifically counteract the responses mediated by many "classical," inflammatory chemokines that act not only via CCR3 but via CCR5 as well.     

Heterologous desensitization of T cell functions by CCR5 and CXCR4 ligands: inhibition of cellular signaling,adhesion and chemotaxis

T cells migrate into inflamed sites through the extracellular matrix (ECM) in response to chemotactic areas and are then simultaneously or sequentially exposed to multiple chemotactic ligands. We examined the responses of human peripheral blood T cells, present in an ECM-like context, to combinatorial signaling transduced by SDF-1alpha (CXCL12), and two CCR5 ligands, RANTES (CCL5) and MIP-1beta (CCL4). Separately, these chemokines, at G protein-coupled receptor (GPCR)-stimulating concentrations, induced T cell adhesion to fibronectin (FN) and T cell chemotaxis. However, the pro-adhesive and pro-migratory capacities of SDF-1alpha and RANTES or MIP-1beta were mutually suppressed by the simultaneous or sequential exposure of the cells to these CCR5 or CXCR4 ligands. This cross-talk did not involve the internalization of the SDF-1alpha receptor, CXCR4, but rather, a decrease in phosphorylation of ERK and Pyk-2, as well as inhibition of Ca(2+) mobilization. Strikingly, early CXCR4 signaling of phosphatidylinositol-3-kinase, detected by SDF-1alpha-induced AKT phosphorylation, was insensitive to RANTES-CCR5 signals. Accordingly, early chemotaxis to SDF-1alpha was not susceptible to CCR5 occupancy, whereas late stages of T cell chemotaxis were markedly down-regulated. This is an example of a specialized functional desensitization of heterologous chemokine receptors that induces GPCR interference with T cell adhesion to ECM ligands and chemotaxis within chemokine-rich extravascular contexts.