Differences in CXCR4-mediated signaling in B cells

CXCR4: from B-cell development to B cell-mediated diseases

Chemokine receptors are members of the G protein-coupled receptor superfamily. The C-X-C chemokine receptor type 4 (CXCR4), one of the most studied chemokine receptors, is widely expressed in hematopoietic and immune cell populations. It is involved in leukocyte trafficking in lymphoid organs and inflammatory sites through its interaction with its natural ligand CXCL12. CXCR4 assumes a pivotal role in B-cell development, ranging from early progenitors to the differentiation of antibody-secreting cells. This review emphasizes the significance of CXCR4 across the various stages of B-cell development, including central tolerance, and delves into the association between CXCR4 and B cell-mediated disorders, from immunodeficiencies such as WHIM (warts, hypogammaglobulinemia, infections, and myelokathexis) syndrome to autoimmune diseases such as systemic lupus erythematosus. The potential of CXCR4 as a therapeutic target is discussed, especially through the identification of novel molecules capable of modulating specific pockets of the CXCR4 molecule. These insights provide a basis for innovative therapeutic approaches in the field.

Case Report: Altered NK Cell Compartment and Reduced CXCR4 Chemotactic Response of B Lymphocytes in an Immunodeficient Patient With HPV-Related Disease

The study of inborn errors of immunity (IEI) provides unique opportunities to elucidate the microbiome and pathogenic mechanisms related to severe viral infection. Several immunological and genetic anomalies may contribute to the susceptibility to develop Human Papillomavirus (HPV) pathogenesis. They include different acquired immunodeficiencies, EVER1-2 or CIB1 mutations underlying epidermodysplasia verruciformis (EV) syndrome and multiple IEI. Whereas EV syndrome patients are specifically unable to control infections with beta HPV, individuals with IEI show broader infectious and immune phenotypes. The WHIM (warts, hypogammaglobulinemia, infection, and myelokathexis) syndrome caused by gain-of-CXCR4-function mutation manifests by HPV-induced extensive cutaneous warts but also anogenital lesions that eventually progress to dysplasia. Here we report alterations of B and NK cells in a female patient suffering from cutaneous and mucosal HPV-induced lesions due to an as-yet unidentified genetic defect. Despite no detected mutations in CXCR4, B but not NK cells displayed a defective CXCR4-dependent chemotactic response toward CXCL12. In addition, NK cells showed an abnormal distribution with an expanded CD56^bright cell subset and defective cytotoxicity of CD56^dim cells. Our observations extend the clinical and immunological spectrum of IEI associated with selective susceptibility toward HPV pathogenesis, thus providing new insight on the immune control of HPV infection and potential host susceptibility factors.

Mesenchymal lineage cells and their importance in B lymphocyte niches

Early B lymphopoiesis occurs in the bone marrow and is reliant on interactions with numerous cell types in the bone marrow microenvironment, particularly those of the mesenchymal lineage. Each cellular niche that supports the distinct stages of B lymphopoiesis is unique. Different cell types and signaling molecules are important for the progressive stages of B lymphocyte differentiation. Cells expressing CXCL12 and IL-7 have long been recognized as having essential roles in facilitating progression through stages of B lymphopoiesis. Recently, a number of other factors that extrinsically mediate B lymphopoiesis (positively or negatively) have been identified. In addition, the use of transgenic mouse models to delete specific genes in mesenchymal lineage cells has further contributed to our understanding of how B lymphopoiesis is regulated in the bone marrow. This review will cover the current understanding of B lymphocyte niches in the bone marrow and key extrinsic molecules and signaling pathways involved in these niches, with a focus on how mesenchymal lineage cells regulate B lymphopoiesis.

Isotype Specific Assembly of B Cell Antigen Receptors and Synergism With Chemokine Receptor CXCR4

Expression of the membrane-bound form of the immunoglobulin (Ig) as part of the antigen receptor is indispensable for both the development and the effector function of B cells. Among five known isotypes, IgM and IgD are the common B cell antigen receptors (BCRs) that are co-expressed in naïve B cells. Despite having identical antigen specificity and being associated with the same signaling heterodimer Igα/Igβ (CD79a/CD79b), IgM and IgD-BCR isotypes functionally differ from each other in the manner of antigen binding, the formation of isolated nanoclusters and in their interaction with co-receptors such as CD19 and CXCR4 on the plasma membrane. With recent developments in experimental techniques, it is now possible to investigate the nanoscale organization of the BCR and better understand early events of BCR engagement. Interestingly, the cytoskeleton network beneath the membrane controls the BCR isotype-specific organization and its interaction with co-receptors. BCR triggering results in reorganization of the cytoskeleton network, which is further modulated by isotype-specific signals from co-receptors. For instance, IgD-BCR is closely associated with CXCR4 on mature B cells and this close proximity allows CXCR4 to employ the BCR machinery as signaling hub. In this review, we discuss the functional specificity and nanocluster assembly of BCR isotypes and the consequences of cross-talk between CXCR4 and IgD-BCR. Furthermore, given the role of BCR and CXCR4 signaling in the development and survival of leukemic B cells, we discuss the consequences of the cross-talk between CXCR4 and the BCR for controlling the growth of transformed B cells.

Isotype Specific Assembly of B Cell Antigen Receptors and Synergism With Chemokine Receptor CXCR4

Expression of the membrane-bound form of the immunoglobulin (Ig) as part of the antigen receptor is indispensable for both the development and the effector function of B cells. Among five known isotypes, IgM and IgD are the common B cell antigen receptors (BCRs) that are co-expressed in naïve B cells. Despite having identical antigen specificity and being associated with the same signaling heterodimer Igα/Igβ (CD79a/CD79b), IgM and IgD-BCR isotypes functionally differ from each other in the manner of antigen binding, the formation of isolated nanoclusters and in their interaction with co-receptors such as CD19 and CXCR4 on the plasma membrane. With recent developments in experimental techniques, it is now possible to investigate the nanoscale organization of the BCR and better understand early events of BCR engagement. Interestingly, the cytoskeleton network beneath the membrane controls the BCR isotype-specific organization and its interaction with co-receptors. BCR triggering results in reorganization of the cytoskeleton network, which is further modulated by isotype-specific signals from co-receptors. For instance, IgD-BCR is closely associated with CXCR4 on mature B cells and this close proximity allows CXCR4 to employ the BCR machinery as signaling hub. In this review, we discuss the functional specificity and nanocluster assembly of BCR isotypes and the consequences of cross-talk between CXCR4 and IgD-BCR. Furthermore, given the role of BCR and CXCR4 signaling in the development and survival of leukemic B cells, we discuss the consequences of the cross-talk between CXCR4 and the BCR for controlling the growth of transformed B cells.

Calcium Independent Effect of Orai1 and STIM1 in Non-Hodgkin B Cell Lymphoma Dissemination

Ca²⁺ release-activated Ca²⁺ channels, composed of Orai1 and STIM1 (stromal interaction molecule 1) proteins, are the main Ca²⁺ entry mechanism in lymphocytes. Their role in cell migration and metastasis is demonstrated in solid cancers but it remains elusive in malignant hemopathies. Diffuse large B cell lymphoma (DLBCL) is characterized by the dissemination of neoplastic B cells throughout the organism which is under the control of chemokines such as Stromal Derived Factor 1 (SDF-1) and its receptor CXCR4. CXCR4 activation triggers a complex intracellular signaling including an increase in intracellular Ca²⁺ concentration whose role is still unclear. Using pharmacological and genetic approaches, we revealed that STIM1 and Orai1 were responsible for Ca²⁺ influx induced by SDF-1. Furthermore, we provide in vitro and in vivo evidence that they are necessary for basal or SDF-1-induced DLBCL cell migration which is independent of Ca²⁺ entry. We identify that they act as effectors coupling RhoA and ROCK dependent signaling pathway to MLC2 phosphorylation and actin polymerization. Finally, we revealed an alteration of Orai1 and STIM1 expression in extra-nodal DLBCL. Thus, we discovered a novel Ca²⁺-independent but Orai1 and STIM1-dependent signaling pathway involved in basal and CXCR4 dependent cell migration, which could be relevant for DLBCL physiopathology.

Expression of pro- and anti-inflammatory cytokines and chemokines during the ovulatory cycle and effects of aging on their expression in the uterine mucosa of laying hens

The aim of this study was to examine whether cytokines and chemokines expressed in the uterine mucosa play a role in the process of eggshell formation in the chicken uterus. Changes in the expression levels of pro- and anti-inflammatory cytokines and chemokines in the uterine mucosa during an ovulatory cycle (experiment 1) and effects of aging on their expression (experiment 2) were examined. In experiment 1, the expression of the pro-inflammatory cytokines IL1β, IL6, TNFSF15, and IFNγ, and a chemokine CX3CL1 was found to increase during eggshell biomineralization (16 h following oviposition), while anti-inflammatory TGFβ2 expression was found to increase at 4 h following oviposition. In experiment 2, a higher expression of the anti-inflammatory cytokines TGFβ2 and TGFβ3, and chemokines CXCLi2 and CX3CL1, was observed in aged hens than in young hens. A significantly higher number of macrophages and CD8+ T cells were observed in the uterine tissue of aged hens than in young hens. Furthermore, the expression of adhesion molecules associated with leukocytic infiltration was found to be higher in aged hens than in young hens. We conclude that the eggshell formation process may be affected by the pro- and anti-inflammatory cytokines and chemokines. The balanced expressions of these molecules might be disrupted in aged hens.

The analysis of heterotaxy patients reveals new loss-of-function variants of GRK5

G protein-coupled receptor kinase 5 (GRK5) is a regulator of cardiac performance and a potential therapeutic target in heart failure in the adult. Additionally, we have previously classified GRK5 as a determinant of left-right asymmetry and proper heart development using zebrafish. We thus aimed to identify GRK5 variants of functional significance by analysing 187 individuals with laterality defects (heterotaxy) that were associated with a congenital heart defect (CHD). Using Sanger sequencing we identified two moderately frequent variants in GRK5 with minor allele frequencies <10%, and seven very rare polymorphisms with minor allele frequencies <1%, two of which are novel variants. Given their evolutionarily conserved position in zebrafish, in-depth functional characterisation of four variants (p.Q41L, p.G298S, p.R304C and p.T425M) was performed. We tested the effects of these variants on normal subcellular localisation and the ability to desensitise receptor signalling as well as their ability to correct the left-right asymmetry defect upon Grk5l knockdown in zebrafish. While p.Q41L, p.R304C and p.T425M responded normally in the first two aspects, neither p.Q41L nor p.R304C were capable of rescuing the lateralisation phenotype. The fourth variant, p.G298S was identified as a complete loss-of-function variant in all assays and provides insight into the functions of GRK5.

Dysfunctions in the migratory phenotype and properties of circulating immature transitional B cells during HIV-1 infection

OBJECTIVE

The frequency of immature transitional B cells is increased in blood of HIV-1-infected individuals. We investigated whether HIV-1 infection affects expression and function of chemokine receptors important for egress of immature transitional B cells from bone marrow and migration to lymphoid organs.

DESIGN

This is a cross-sectional study analysing the migratory phenotype and function of immature transitional B cells in HIV-1-infected individuals, in relation to antiretroviral treatment and age.

METHODS

Frequency of blood immature transitional B cells and their phenotypic characteristics, including chemokine receptors and a maturation marker, were determined by immunostainings. Migratory capacities were studied in a migration assay.

RESULTS

The increased frequency of immature transitional B cells in untreated HIV-1 infection was normalized in patients receiving antiretroviral treatment; in our cohorts, age did not have an impact on the frequency of circulating immature transitional B cells. Immature transitional B cells from nontreated patients expressed low levels of CD21 molecule. We found an elevated frequency of CXCR3 and CXCR4 expressing immature transitional B cells in treated and nontreated patients. CXCR4 receptor was unresponsive to CXCL12 ligand in in-vitro migration and internalization assays. In addition, CXCR5 expression was downregulated on immature transitional B cells from infected patients, and these cells migrated poorly in response to CXCR5 ligand.

CONCLUSION

Circulating immature transitional B cells from HIV-1-infected patients are not fully mature, probably due to premature egress from bone marrow; these cells showed a phenotype which could impair entry into secondary lymphoid organs. Changes in migratory capacity of immature transitional B cells may affect B-cell maturation during HIV-1 infection.

Altered chemotactic response to CXCL12 in patients carrying GATA2 mutations

GATA2 deficiency-formerly described as MonoMAC syndrome; dendritic cells, monocytes, B cells, and natural killer cell deficiency; familial myelodysplastic syndrome/acute myeloid leukemia; or Emberger syndrome-encompasses a range of hematologic and nonhematologic anomalies, mainly characterized by monocytopenia, B lymphopenia, natural killer cell cytopenia, neutropenia, immunodeficiency, and a high risk of developing acute myeloid leukemia. Herein, we present 7 patients with GATA2 deficiency recruited into the French Severe Chronic Neutropenia Registry, which enrolls patients with all kinds of congenital neutropenia. We performed extended immunophenotyping of their whole blood lymphocyte populations, together with the analysis of their chemotactic responses. Lymphopenia was recorded for B and CD4(+) T cells in 6 patients. Although only 3 patients displayed natural killer cell cytopenia, the CD56(bright) natural killer subpopulation was nearly absent in all 7 patients. Natural killer cells from 6 patients showed decreased CXCL12/CXCR4-dependent chemotaxis, whereas other lymphocytes, and most significantly B lymphocytes, displayed enhanced CXCL12-induced chemotaxis compared with healthy volunteers. Surface expression of CXCR4 was significantly diminished in the patients' natural killer cells, although the total expression of the receptor was found to be equivalent to that of natural killer cells from healthy individual controls. Together, these data reveal that GATA2 deficiency is associated with impaired membrane expression and chemotactic dysfunctions of CXCR4. These dysfunctions may contribute to the physiopathology of this deficiency by affecting the normal distribution of lymphocytes and thus potentially affecting the susceptibility of patients to associated infections.

BTK inhibition results in impaired CXCR4 chemokine receptor surface expression, signaling and function in chronic lymphocytic leukemia

Bruton's tyrosine kinase (BTK) is involved in the regulation of B-cell growth, migration and adhesion. The importance of BTK in cell trafficking is emphasized by the clonal contraction proceeded by lymphocytosis typical for the enzyme inhibitor, ibrutinib, in B-cell malignancies, including chronic lymphocytic leukemia (CLL). Here, we investigated BTK regulation of leukemic B-cell trafficking in a mouse model of aggressive TCL1 CLL-like disease. Inhibiting BTK by ibrutinib reduced surface membrane (sm) levels of CXCR4 but not CXCR5, CD49d and other adhesion/homing receptors. Decreased smCXCR4 levels resulted from blocking receptor signal transduction, which in turn aborted cycling from and to the membrane. This resulted in rapid re-distribution of CLL cells from spleens and lymph nodes into the circulation. CLL cells with impaired smCXCR4 from BTK inhibition failed to home to spleens. These functional changes mainly resulted from inhibition of CXCR4 phosphorylation at Ser339, mediated directly by blocking BTK enzymatic activity and indirectly by affecting the function of downstream targets PLCγ2 and PKCμ, and eventually synthesis of PIM-1 and BTK itself. Our data identify CXCR4 as a key regulator in BTK-mediated CLL-cell retention and have elucidated a complex set of not previously described mechanisms responsible for these effects.

CD99 regulates CXCL12-induced chemotaxis of human plasma cells

Migration of plasma cells (PCs) is crucial for the control of PC survival and antibody production and is controlled by chemokines, most importantly by CXCL12. This study investigated the role of CD99 in CXCL12-induced PC migration. Among B cell subsets in the tonsils, CD99 expression was highest in PCs. CD99 expression increased during in vitro differentiation of germinal center B cells and was highest in PCs. CD99 engagement reduced chemotactic migration of PCs toward CXCL12 and reduced extracellular signal-regulated kinase (ERK) activation by CXCL12. An ERK inhibitor reduced CXCL12-mediated chemotactic migration, which suggests that ERK has a critical role in migration. CD99 engagement did not influence apoptosis, differentiation, or antibody secretion of PCs. We propose a novel role of CD99 in PCs that suppresses ERK activation and chemotactic migration of these cells.

CXCL12/CXCR4 axis in the pathogenesis of acute lymphoblastic leukemia (ALL): a possible therapeutic target

Acute lymphoblastic leukemia (ALL) is the commonest childhood malignancy, accounting for approximately 80 % of leukemia in the pediatric group, and its etiology is unknown. This neoplasia is characterized by male predominance, high-risk features and poor outcome, mainly in recurrence patients and adults. In recent years, advances in the success of childhood ALL treatment were verified, and the rate of cure is over 80 % of individuals. However, there is a considerable scope for improving therapeutic outcome in this neoplasia. Improvements in ALL therapy might readily be achieved by developing additional biomarkers that can predict and refine prognosis in patients with ALL. In normal hematopoietic cells, cytokines provide the stimulus for proliferation, survival, self-renewal, differentiation and functional activation. Abnormalities of cytokines are characteristic in all forms of leukemia, including ALL. The stromal cell-derived factor-1 (SDF-1 or CXCL12) is a member of the CXC chemokine family that binds to CXC chemokine receptor 4 (CXCR4). The CXCL12/CXCR4 axis appears to play a role in dissemination of solid tumors and hematopoietic diseases. Understanding the mechanisms by which ALL cells are disseminated will provide additional information to expand therapeutic approach. Therefore, this review summarizes information relating to ALL cell biology, focusing specifically in a cytokine receptor important axis, CXCL12/CXCR4, that may have implications for novel treatment strategies to improve life expectancy of patients with this neoplasia.

Herpes simplex virus enhances chemokine function through modulation of receptor trafficking and oligomerization

Glycoprotein G (gG) from herpes simplex virus 1 and 2 (HSV-1 and HSV-2, important human neurotropic pathogens) is the first viral chemokine-binding protein found to potentiate chemokine function. Here we show that gG attaches to cell surface glycosaminoglycans and induces lipid raft clustering, increasing the incorporation of CXCR4 receptors into these microdomains. gG induces conformational rearrangements in CXCR4 homodimers and changes their intracellular partners, leading to sustained, functional chemokine/receptor complexes at the surface. This results in increased chemotaxis dependent on the cholesterol content of the plasma membrane and receptor association to Src-kinases and phosphatidylinositol-3-kinase signalling pathways, but independent of clathrin-mediated endocytosis. Furthermore, using electron microscopy, we show that such enhanced functionality is associated with the accumulation of low-order CXCR4 nanoclusters. Our results provide insights into basic mechanisms of chemokine receptor function and into a viral strategy of immune modulation.

Peripheral regulatory cells immunophenotyping in primary Sjögren's syndrome: a cross-sectional study

Introduction

IL-10--producing B cells, Foxp3-expressing T cells (Tregs) and the IDO-expressing dendritic cells (pDC) are able to modulate inflammatory processes, to induce immunological tolerance and, in turn, to inhibit the pathogenesis of autoimmune disease.

The aim of the study was to characterize and to enumerate peripheral IL-10--producing B cells, Tregs and pDCregs in primary Sjögren's Syndrome (pSS) patients in regard of their clinical and serologic activity.

Methods

Fifty pSS patients and 25 healthy individuals were included in the study. CD19⁺--expressing peripheral B lymphocytes were purified by positive selection. CD19⁺/CD24^hi/CD38^hi/IL-10--producing B cells, CD4⁺/CD25^hi/Foxp3⁺ and CD8⁺/CD28^-/Foxp3⁺ Tregs, as well as CCR6⁺/CD123⁺/IDO⁺ DCs, were quantitated by flow cytometry.

Results

Immature/transitional circulating IgA⁺ IL-10--producing B cells had higher levels in pSS patients versus control group, whereas CD19⁺/CD38^hi/IgG⁺/IL-10⁺ cells had lower percentage versus control. Indeed CD19⁺/CD24^hi/CD38^hi/CD5⁺/IL-10⁺, CD19⁺/CD24^hi/CD38^hi/CD10⁺/IL-10⁺, CD19⁺/CD24^hi/CD38^hi/CD20⁺/IL-10⁺, CD19⁺/CD24^hi/CD38^hi/CD27^-/IL-10⁺, and CD19⁺/CD24^hi/CD38^hi/CXCR7⁺/IL-10⁺ cells had higher frequency in clinical inactive pSS patients when compared with control group. Remarkably, only percentages of CD19⁺/CD24^hi/CD38^hi/CD10⁺/IL-10⁺ and CD19⁺/CD24^hi/CD38^hi/CD27^-/IL-10⁺ subsets were increased in pSS serologic inactive versus control group (P < 0.05). The percentage of IDO-expressing pDC cells was higher in pSS patients regardless of their clinical or serologic activity. There were no statistically significant differences in the percentage of CD4⁺/CD25^hi/Foxp3⁺ Tregs between patient groups versus controls. Nonetheless, a decrease in the frequency of CD8⁺/CD28^-/Foxp3⁺ Tregs was found in inactive pSS patients versus controls (P < 0.05).

Conclusions

The findings of this exploratory study show that clinical inactive pSS patients have an increased frequency of IL-10--producing B cells and IDO-expressing pDC cells.

Multiple levels of chemokine receptor regulation in the control of mouse natural killer cell development

Chemokines play a fundamental role in lymphocyte development, mainly attributable to the control of the correct localization in the proper microenvironments of cells undergoing maturation. Natural killer (NK) cell development occurs in the bone marrow (BM) where their localization is regulated by the balance of chemokine function in cell retention into tissues and mobilization into circulation. In addition, NK cells from several extra-medullary tissues are phenotypically and functionally different from their circulating counterpart suggesting that maturation can be completed in organs other than BM. Indeed, a role of chemokines in NK cell localization into tissues during homeostatic conditions is also documented. In this review, we summarize the current notion related to the relevance of several chemokine/chemokine receptor axes in NK cell development with a focus on the regulation of their expression and function.

Absence of CC chemokine receptors 2a and 2b from human adipose lineage cells

Previous results have suggested the existence of receptors for monocyte chemoattractant protein-1 (MCP-1), CC chemokine receptors 2 (CCR2), in human adipocytes and their involvement in mediating effects of MCP-1 on adipocyte functions. However, the presence of CCR2 present on non-adipose-lineage cells of adipose tissue has not been excluded. We have used human Simpson-Golabi-Behmel-Syndrome (SGBS) preadipocytes and in-vitro-differentiated mature adipocytes to investigate the expression of CCR2 in human (pre)adipocytes. We found that the cells are devoid of CCR2 receptor protein and mRNA expression and fail to respond to treatment with all known CCR2 chemokine agonists. CCR2 is also absent from (pre)adipocytes prepared in vitro from human multipotent adipose-derived stem cells, bone-marrow-derived mesenchymal stem cells, or from primary (pre)adipocytes. Conditions mimicking proinflammatory changes in adipose tissue did not induce CCR2 receptor expression. We conclude that CCR2 is absent from human adipose lineage cells. Functional effects previously described for MCP-1 in human adipose tissue may be mediated indirectly through paracrine effects on non-adipose-lineage cells or by a (pre)adipocyte receptor for MCP-1 distinct from CCR2.

Expression of CXCL12 receptors in B cells from Mexican Mestizos patients with systemic Lupus erythematosus

BACKGROUND

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease characterized by B-cell hyper-reactivity and the production of pathogenic anti-nuclear-directed auto-antibodies (Abs). B-cell ontogeny is partly dependent on the CXCL12/CXCR4 axis for which the contribution to SLE pathogenesis remains unclear. CXCR7, the novel receptor for CXCL12, is differentially expressed among memory B-cell subsets. However, its biological role in SLE remains to be explored.

METHODS

Relative CXCR4 and CXCR7 expression levels were compared by quantitative PCR in leukocytes from blood samples of 41 Mexican Mestizos patients with SLE and 45 ethnicity-matched healthy subjects. Intracellular and membrane expression of both receptors was analyzed by flow cytometry in naive and Ab-secreting B cells. B-cell responsiveness to CXCL12 was investigated using Transwell-based chemotaxis assays. Data were analyzed using the Kruskal-Wallis test for comparisons of values amongst healthy controls and patients with inactive or active SLE, and non-parametrically using the Mann-Whitney U-test for multiple comparisons and unpaired samples. Correlations were determined by Spearman's ranking.

RESULT

SLE leukocytes displayed reduced levels of CXCR4 and CXCR7 transcripts. In SLE patients, a significant defect in CXCR4 expression was detected at the surface of naive and Ab-secreting B cells, associated with an abnormal intracellular localization of the receptor. CXCR7 predominantly localized in cytosolic compartments of B cells from healthy and SLE individuals. Disease activity did not impact on these expression patterns. Altered receptor compartmentalization correlated with an impaired CXCL12-promoted migration of SLE B cells.

CONCLUSIONS

Our data highlight a down-regulation of CXCL12 receptors on circulating B cells from SLE patients that likely influences their migratory behavior and distribution.

Peripheral regulatory cells immunophenotyping in kidney transplant recipients with different clinical profiles: a cross-sectional study

Regulatory Foxp3-expressing T cells (Tregs), IL-10-producing B cells (Bregs), and IDO-expressing dendritic cells (DCregs) downregulate inflammatory processes and induces peripheral tolerance. These subpopulations also might participate in maintaining allograft immunological quiescence in kidney transplant recipients (KTRs) with an excellent long-term graft function under immunosuppression (ELTGF). The aim of the study was to characterize and to enumerate peripheral Tregs, Bregs, and DCregs in KTR with an ELTGF for more than 5 years after transplant. Fourteen KTR with an ELTGF, 9 KTR with chronic graft dysfunction (CGD), and 12 healthy donors (HDs) were included in the study. CD19⁺-expressing peripheral B lymphocytes were purified by positive selection. IL-10-producing B cells, CD4⁺/CD25^hi, and CD8⁺/CD28⁻ Tregs, as well as CCR6⁺/CD123⁺/IDO⁺ DCs, were quantitated by flow cytometry. IL-10-producing Bregs (immature/transitional, but not CD19⁺/CD38^hi/CD24^hi/CD27⁺B10 cells), CCR6⁺/CD123⁺/IDO⁺ DCs, and Tregs from ELTGF patients had similar or higher percentages versus HD (P < 0.05). By contrast, number of Tregs, DCregs, and Bregs except for CD27⁺B10 cells from CGD patients had lower levels versus HD and ELTGF patients (P < 0.05). The findings of this exploratory study might suggest that in ELTGF patients, peripheral tolerance mechanisms could be directly involved in the maintenance of a quiescent immunologic state and graft function stability.

CXCR7 impact on CXCL12 biology and disease

It is known that the chemokine receptor CXCR7 (RDC1) can be engaged by both chemokines CXCL12 (SDF-1) and CXCL11 (I-TAC), but the exact expression pattern and function of CXCR7 is controversial. CXCR7 expression seems to be enhanced during pathological inflammation and tumor development, and emerging data suggest this receptor is an attractive therapeutic target for autoimmune diseases and cancer. CXCR7/CXCR4 heterodimerization, β-arrestin-mediated signaling, and modulation of CXCL12 responsiveness by CXCR7 suggest that the monogamous CXCR4/CXCL12 signaling axis is an oversimplified model that needs to be revisited. Consequently, research into CXCR7 biology is of great interest and further studies are warranted. This review summarizes recent findings about the CXCR7 receptor and analyses its impact on understanding the roles of CXCL12 biology in health and disease.

Proper desensitization of CXCR4 is required for lymphocyte development and peripheral compartmentalization in mice

Desensitization controls G protein-dependent signaling of chemokine receptors. We investigate the physiologic implication of this process for CXCR4 in a mouse model harboring a heterozygous mutation of the Cxcr4 gene, which engenders a desensitization-resistant receptor. Such anomaly is linked to the warts, hypogammaglobulinemia, infections, myelokathexis (WHIM) syndrome, a human rare combined immunodeficiency. Cxcr4(+/mutant(1013)) mice display leukocytes with enhanced responses to Cxcl12 and exhibit leukopenia as reported in patients. Treatment with CXCL12/CXCR4 antagonists transiently reverses blood anomalies, further demonstrating the causal role of the mutant receptor in the leukopenia. Strikingly, neutropenia occurs in a context of normal bone marrow architecture and granulocyte lineage maturation, indicating a minor role for Cxcr4-dependent signaling in those processes. In contrast, Cxcr4(+/1013) mice show defective thymopoiesis and B-cell development, accounting for circulating lymphopenia. Concomitantly, mature T and B cells are abnormally compartmentalized in the periphery, with a reduction of primary follicles in the spleen and their absence in lymph nodes mirrored by an unfurling of the T-cell zone. These mice provide a model to decipher the role of CXCR4 desensitization in the homeostasis of B and T cells and to investigate which manifestations of patients with WHIM syndrome may be overcome by dampening the gain of CXCR4 function.

LPS-induced migration of peritoneal B-1 cells is associated with upregulation of CXCR4 and increased migratory sensitivity to CXCL12

B-1 cells, which constitute a predominant lymphocyte subset in serosal cavities and produce most of natural antibodies, are subdivided into the CD5(+) B-1a and CD5(-) B-1b cell subpopulations, but the differential roles of B-1a and B-1b cells are not well understood. We report that B-1a cells preferentially migrate out of the peritoneal cavity and upregulate the expression of CXCR4 with heightened sensitivity to CXCL12 and CXCL13 upon LPS treatment compared to B-1b and B-2 cells. Whereas B-1a cells were slightly more abundant than B-1b and B-2 cells in the homeostatic condition, the number of B-1a cells preferentially decreased 48 hr after LPS treatment. The decrease in the peritoneal B-1a cell number was accompanied with increased migration of B-1a cells toward CXCL-12 and CXCL-13 in in vitro transmigration assay using peritoneal B cells from LPS treated mice. The expression level of CXCR4, but not of CXCR5, was also more prominently increased in B-1a cells upon LPS stimulation. LPS-stimulated B-1a cells did not accumulate in omental milky spots in contrast to B-2 cells. These results suggest that B-1a cells actively migrate out of the peritoneal cavity through the regulation of the migratory responsiveness to chemokines and actively participate in systemic immune responses.

Attenuation of CXCR4 responses by CCL18 in acute lymphocytic leukemia B cells

CCL18 and CXCL12 are homeostatic chemokines with high constitutive concentrations in serum. Elevated levels of CCL18 have been described in various diseases including childhood acute lymphocytic leukemia (ALL) but its functions remain poorly characterized. Its receptor has not been identified, but functional cellular responses like lymphocyte chemotaxis have been described. CXCL12 is a pivotal chemokine for hematopoiesis and B cell homing processes. We demonstrate that CCL18 interferes with CXCL12-mediated pre-B ALL cell activation. CXCL12-induced calcium mobilization, chemotaxis, pseudo-emperipolesis and cellular proliferation could be significantly reduced by CCL18 in pre-B ALL cell lines. The results could be observed in primary cells from patients suffering from pre-B ALL, but not in cells from patients suffering from common ALL. Direct effects of CCL18 on the receptor for CXCL12, CXCR4, could be excluded. Moreover, we found that CCL18 modulations of CXCL12-induced responses are mediated through the chemokine-like receptor GPR30. CCL18 bound to GPR30 expressing cells, and antibodies against GPR30 abolished this binding as well as CCL18-mediated functional effects. We also observed that, CCL18 interferes with the activation of GPR30 by previously identified ligands (17β-estradiol and chemical agonists). We therefore suggest that CCL18 is an important modulator of CXCR4-dependent responses in pre-B ALL cells via interactions with GPR30.

CXCL12-induced glioblastoma cell migration requires intermediate conductance Ca2+-activated K+ channel activity

The activation of ion channels is crucial during cell movement, including glioblastoma cell invasion in the brain parenchyma. In this context, we describe for the first time the contribution of intermediate conductance Ca2+-activated K (IKCa) channel activity in the chemotactic response of human glioblastoma cell lines, primary cultures, and freshly dissociated tissues to CXC chemokine ligand 12 (CXCL12), a chemokine whose expression in glioblastoma has been correlated with its invasive capacity. We show that blockade of the IKCa channel with its specific inhibitor 1-[(2-chlorophenyl) diphenylmethyl]-1 H-pyrazole (TRAM-34) or IKCa channel silencing by short hairpin RNA (shRNA) completely abolished CXCL12-induced cell migration. We further demonstrate that this is not a general mechanism in glioblastoma cell migration since epidermal growth factor (EGF), which also activates IKCa channels in the glioblastoma-derived cell line GL15, stimulate cell chemotaxis even if the IKCa channels have been blocked or silenced. Furthermore, we demonstrate that both CXCL12 and EGF induce Ca2+ mobilization and IKCa channel activation but only CXCL12 induces a long-term upregulation of the IKCa channel activity. Furthermore, the Ca2+-chelating agent BAPTA-AM abolished the CXCL12-induced, but not the EGF-induced, glioblastoma cell chemotaxis. In addition, we demonstrate that the extracellular signal-regulated kinase (ERK)1/2 pathway is only partially implicated in the modulation of CXCL12-induced glioblastoma cell movement, whereas the phosphoinositol-3 kinase (PI3K) pathway is not involved. In contrast, EGF-induced glioblastoma migration requires both ERK1/2 and PI3K activity. All together these findings suggest that the efficacy of glioblastoma invasiveness might be related to an array of nonoverlapping mechanisms activated by different chemotactic agents.

Molecular cloning, characterization, and expression analysis of the CXCR4 gene from Turbot: Scophthalmus maximus

Chemokine receptor 4 (CXCR4) belongs to the large superfamily of G protein-coupled receptors. The EST sequence of CXCR4 from turbot (Scophthalmus maximus L.) was obtained from a subtractive cDNA library. In the present study, the full-length cDNA sequence of turbot CXCR4 was obtained, and sequence analysis indicated that its primary structure was highly similar to CXCR4 from other vertebrates. Quantitative real-time PCR demonstrated that the highest expression level of turbot CXCR4 was in the spleen following injection with physiological saline (PS). After turbot were challenged with Vibrio harveyi, the lowest expression level of CXCR4 was detected at 8 hours in the spleen and 12 hours in the head kidney, and then increased gradually to 36 hours. These findings suggested that CXCR4 may play a significant role in the immune response of turbot.

Regulatory T cells and their prognostic value for patients with squamous cell carcinoma of the head and neck

Regulatory T cells (Treg) are important regulators of anti-cancer immune responses, and an increase in Treg frequency was observed in the blood of cancer patients. Blood samples from 112 patients with head and neck squamous cell carcinoma antigen (HNSCC) were obtained at the time of tumour diagnosis, and lymphocyte subpopulations (CD3⁺; CD3⁻CD16⁺CD56⁺; CD4⁺; CD8⁺; CD19⁺; CD4⁺CD45RA⁺) with emphasis on Treg counts (CD3⁺CD4⁺CD25⁺), complete blood count and tumour markers (squamous cell carcinoma [SCC]; CEA; α-1-antitrypsin [AAT]; Cyfra 21–1; C-reactive protein [CRP]) were analysed. The data were grouped according to TNM classification, and their significance for the course of the disease at an interval of 1 year after the end of the therapy was determined. The percentage of CD8⁺ cells increased and the CD/D8 ratio decreased with tumour grade. The ratio of B lymphocytes decreased in patients with locoregional metastases (11.25%versus 9.22%). Treg (15.2%) and CD4⁺ cells (45.3%) increased, while NK cells (11.8%) decreased in HNSCC patients compared to controls (9.0%, 38.1% and 15.8%, respectively). The data obtained at time of diagnosis were used to assess the significance of tumour markers (SCC, Cyfra 21–1 and AAT) for evaluation of prognosis. The erythrocyte counts (4.64 × 10¹²/l versus 4.45 × 10¹²/l) and haemoglobin levels (14.58 g/dl versus 14.05 g/dl) decreased, while Treg counts (8.91%versus 15.70%) increased in patients with early recurrence. Our results show that examination of these parameters could be helpful for prognostication in HNSCC patients and aid improvement of treatment strategy.

How chemokines invite leukocytes to dance

A prominent activity of the chemokine system is the regulation of leukocyte trafficking. Here we summarize recent findings on the initial steps in chemokine receptor-induced signal transduction in leukocytes. In particular, we discuss the potential influences of the formation of oligomers of ligand and receptor and of coupling between chemokine signals and regulators of the cytoskeleton, such as small GTPases.

Generation and characterization of novel local and metastatic human neuroblastoma variants

Neuroblastoma (NB) is the most commonly occurring solid tumor in children. The disease usually arises in the adrenal medulla, and it is characterized by a remarkable heterogeneity in its progression. Most NB patients with an advanced disease have massive bone marrow infiltration at diagnosis. Lung metastasis represents a widely disseminated stage and is typically considered to be a terminal event. Much like other malignancies, NB progression is a complex, multistep process. The expression, function, and significance of the various factors involved in NB progression must be studied in relevant in vivo and in vitro models. Currently, models consisting of metastatic and nonmetastatic cell variants of the same genetic background exist for several types of cancer; however, none exists for NB. In the present study, we describe the generation of a NB metastasis model. SH-SY5Y and MHH-NB-11 NB cells were inoculated orthotopically into the adrenal glands of athymic nude mice. Neuroblastoma cells metastasizing to the lungs were isolated from mice bearing adrenal tumors. Lung metastatic variants were generated by repeated cycles of in vivo passage. Characterization of these variants included cellular morphology and immunophenotyping in vitro, aggressiveness in vivo, and various biologic parameters in vitro. The NB metastatic variant in each model displayed unique properties, and both metastatic variants demonstrated a metastatic phenotype in vivo. These reproducible models of human NB metastasis will serve as an unlimited source of transcriptomic and proteomic material. Such models can facilitate future studies on NB metastasis and the identification of novel NB biomarkers and targets for therapy.

SOCS3 protein developmentally regulates the chemokine receptor CXCR4-FAK signaling pathway during B lymphopoiesis

The chemokine CXCL12 induces prolonged focal adhesion kinase (FAK) phosphorylation and sustained proadhesive responses in progenitor bone-marrow (BM) B cells, but not in mature peripheral B cells. Here we demonstrate that suppressor of cytokine signaling 3 (SOCS3) regulated CXCL12-induced FAK phosphorylation through the ubiquitin-proteasome pathway. CXCL12 triggered increased FAK ubiquitination in mature B cells, but not in progenitor B cells. Accordingly, SOCS3 expression was low in progenitor B cells, increased in immature B cells, and highest in mature B cells. SOCS3 overexpression in pro-B cells impaired CXCL12-induced FAK phosphorylation and proadhesive responses. Conversely, SOCS3-deficient mature B cells from Cre(MMTV)Socs3(fl/fl) mice exhibited prolonged FAK phosphorylation and adhesion to VCAM-1. In contrast to wild-type mice, Cre(MMTV)Socs3(fl/fl) mice had a 2-fold increase in immature B cells, which were evenly distributed in endosteal and perisinusoidal BM compartments. We propose that the developmental regulation of CXCR4-FAK signaling by SOCS3 is an important mechanism to control the lodgement of B cell precursors in the BM microenvironment.

Expression pattern and cellular sources of chemokines in primary central nervous system lymphoma

The expression pattern of a subset of chemokines and their corresponding receptors was investigated in primary central nervous system lymphomas (PCNSL). The tumor cells consistently expressed CXCR4, CXCL12, CXCR5, and CXCL13, both at mRNA and protein levels. Cerebral endothelial cells were positive for CXCL12 and CXCL13, while reactive astrocytes and microglial cells expressed CXCL12, CCR5, and CCR6. Inflammatory T cells in PCNSL were characterized by CCR5 and CCR6 positivity. Taken together, our data indicate a cell type-specific repertoire of chemokine and chemokine receptor expression in PCNSL suggesting that chemokine-mediated interactions facilitate crossing of the blood-brain barrier as well as intracerebral dissemination of PCNSL cells. In addition, chemokines expressed by tumor cells may contribute to induction of reactive glial changes and influence the composition of inflammatory infiltrates in PCNSL. Therefore, cell type specific expression of distinct chemokine profiles likely plays a role in the pathogenesis of PCNSL and may contribute to their characteristic histological appearance.