The CXCR7 chemokine receptor promotes B-cell retention in the splenic marginal zone and serves as a sink for CXCL12

Abstract

IntroductionLocalization and retention of B cells in the marginal zone (MZ) depends on antigenic specificity, 1,2 interactions between integrins and their receptors, 3 and signaling by the lysophospholipid, S1P, through the S1P 1 receptor. 4 Although MZ B cells are considered nonrecirculatory, exposure to cognate Ag or bacterial products causes them to relocalize from the MZ to the splenic white pulp, 4 providing for efficient delivery of captured Ags to follicular dendritic cells. 5 Although no direct evidence links chemokine involvement to MZ B-cell localization and retention, the MZs are strikingly reduced or absent in mice deficient in a series of factors that may act downstream of chemokine receptors. 6 Recent studies, however, showed that transcripts for the chemokine receptor, CXCR7, were expressed at much higher levels by mouse MZ than follicular (FO) B cells. 7-9 CXCR7 has variously been reported to function as the primary receptor and scavenger for CXCL12, 8,10,11 a modulator of CXCR4 activity, or to act directly on different tumor types. 11,12 This prompted us to determine whether CXCR7 and its ligands, CXCL11 and CXCL12, 11,13 might influence MZ B-cell biology by taking advantage of recently developed CXCR7-specific mAbs and small molecule inhibitors. We found that CXCR7 was expressed on MZ but not on FO B cells and that treatment with inhibitors disrupted the normal organization of the MZ, altered MZ B-cell numbers, and increased serum levels of CXCL12, resulting in altered homeostasis of granulocytes. Methods Flow cytometrySplenic single-cell suspensions were blocked with a Fc receptor-blocking mAb, 2.4G2, and stained with fluorochrome-labeled Abs specific for B220, CD19, CD23, CD21, Gr-1, CD3, CD11b, ␣L, ␣4, ␤1, and ␣4␤7 (purchased from BD Biosciences or eBioscience). In some experiments, cells were stained with anti-CXCR7 mAb (11G8; provided by ChemoCentryx) followed by FITC-conjugated secondary Ab. An isotype control Ab was included as a negative control. The cells were analyzed by FACSCalibur or LSRII (BD Biosciences), and the data were analyzed by FlowJo Version 7.5.5 software (TreeStar). Animals, treatment, serum CXCL12, and histologic analysisFVB and B6 mice (2-6 months old) were purchased from The Jackson Laboratory. FVB mice have unusually large MZs, 14 whereas B6 mice are functionally deficient in CXCL11 because of a deletion in the coding sequence. 15 Mice were injected subcutaneously with CXCR7 antagonists CCX754 (100 mg/kg twice daily) or CCX771 (30 mg/kg daily; provided by ChemoCentryx) for 2-7 days. The specificity, half-life, and effect of the inhibitors have been reported previously. 11,16,17 Control mice were injected with equal volumes of vehicles (10% Captisol). The spleens were analyzed by flow cytometry and confocal microscopy, as described previously, with the use of labeled mAb to IgM, metallophilic macrophages (MOMA-1), and marginal sinus epithelial cells (MAdCAM-1). 18 The slides were imaged at 20°C with the use of ϫ10 and ϫ20 oil-immersion lenses on a Leica SP2 4-chanel c...

Deregulation of ETS1 and FLI1 contributes to the pathogenesis of diffuse large B-cell lymphoma

“…[39][40][41][42] Although less is known regarding the role of CXCR7, 43,44 CXCR5 and CXCR4 regulate the development and the trafficking of B cells within the GC. 45 In normal lymphoid tissue, CXCR4 is highly expressed in the dark zone of the GC, attracting the centroblasts, whereas CXCR5 expression is in the light zone and contributes to attracting B cells to the area and is then downregulated during plasmacytic differentiation.…”

Chemokine receptors in gastric MALT lymphoma: loss of CXCR4 and upregulation of CXCR7 is associated with progression to diffuse large B-cell lymphoma

“…This may cause proliferative and pro-survival effects in the lymphoma cells. As pharmacological blockage of the interaction of CXCL12 with CXCR7 leads to retention of marginal zone B cells in the splenic marginal zone, 56 it might be speculated that CXCR7-CXCL12 interaction is essential for the homing process of MALT lymphoma and extranodal diffuse large B-cell lymphoma cells to the gastric mucosa.…”

Intrinsic Molecular Factors Cause Aberrant Expansion of the Splenic Marginal Zone B Cell Population in Nonobese Diabetic Mice

“…At these sites, B cells gain access to various molecular factors that drive both the differentiation and survival of the MZ B cell subset (38). Proteins encoded by S1pr3 and Cxcr7 (named sphingosine-1-phosphate receptor-3 [S1PR 3 ] and CXCR7, respectively) have been shown to play specific roles in the migration and/or retention of B cells within the MZ niche (4,46,47). Our previous study showed that NOD MZ B cells had an increased capacity for migration toward sphingosine-1-phosphate (S1P) compared with those from B6 mice in chemotaxis assays, which was dependent on their elevated expression of S1PR 3 (12).…”

“…CXCR7 acts as a scavenging receptor that binds and degrades CXCL12 and CXCL11, preventing them from interacting with CXCR4 and CXCR3, respectively (48,49). A recent report by Wang et al (47) demonstrated that CXCR7 plays a role in guiding B cells to the MZ by restricting CXCL12 from binding to CXCR4 and that blocking CXCR7 with small molecule inhibitors decreased localization of MZ B cells within this niche. Consistent with their higher gene expression of Cxcr7 (Fig.…”