CCR5-binding chemokines modulate CXCL12 (SDF-1)-induced responses of progenitor B cells in human bone marrow through heterologous desensitization of the CXCR4 chemokine receptor

Dynamic immune ecosystem of dengue infection revealed by single-cell sequencing

Dengue is the most common human arboviral disease worldwide, which can result in severe complications. A dysfunctional immune response in dengue infective patients is a recurrent theme impacting symptoms and mortality, but the heterogeneity and dynamics of immune infiltrates during dengue infection remain poorly characterized. Here, we identified the immune cell types in scRNA-seq data from 13127 cells of 10 dengue infective patients and discovered the dynamic immune ecosystems of dengue infection. Notably, genes that exhibited higher expression in specific cell types play important roles in response to virus infection in a module manner. Transcription factors (TFs) are the major regulators (i.e., PAX5, IRF7, KLF4, and IRF8) that can potentially regulate infection-related genes. We demonstrated that the dynamic rewired regulatory network during dengue infection. Moreover, our data revealed the complex cell-cell communications from control to fever and severe dengue patients and prevalent cell-cell communication rewiring was observed. We further identified the IFN-II and CXCL signaling pathways that medicated the communications and play important roles in dengue infection. Together, our comprehensive analysis of dynamic immune ecosystem of dengue infection provided novel insights for understanding the pathogenesis of and developing effective therapeutic strategies for dengue infection.

A Single-Cell Atlas of Tumor-Infiltrating Immune Cells in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies with limited treatment options. To guide the design of more effective immunotherapy strategies, mass cytometry was employed to characterize the cellular composition of the PDAC-infiltrating immune cells. The expression of 33 protein markers was examined at the single-cell level in more than two million immune cells from four types of clinical samples, including PDAC tumors, normal pancreatic tissues, chronic pancreatitis tissues, and peripheral blood. Based on the analyses, we identified 23 distinct T-cell phenotypes, with some cell clusters exhibiting aberrant frequencies in the tumors. Programmed cell death protein 1 (PD-1) was extensively expressed in CD4+ and CD8+ T cells and coexpressed with both stimulatory and inhibitory immune markers. In addition, we observed elevated levels of functional markers, such as CD137L and CD69, in PDAC-infiltrating immune cells. Moreover, the combination of PD-1 and CD8 was used to stratify PDAC tumors from The Cancer Genome Atlas database into three immune subtypes, with S1 (PD-1+CD8+) exhibiting the best prognosis. Further analysis suggested distinct molecular mechanisms for immune exclusion in different subtypes. Taken together, the single-cell protein expression data depicted a detailed cell atlas of the PDAC-infiltrating immune cells and revealed clinically relevant information regarding useful cell phenotypes and targets for immunotherapy development.

BAFF Inhibition Effectively Suppresses the Development of Anti-HLA.A2 Antibody in the Highly Sensitized Mouse Model

B cell activating factor (BAFF) is a cytokine that plays a role in the survival, proliferation and differentiation of B cells. We proposed to observe the effects of BAFF inhibition on the humoral immune responses of an allosensitized mouse model using HLA.A2 transgenic mice. Wild-type C57BL/6 mice were sensitized with skin allografts from C57BL/6-Tg (HLA-A2.1)1Enge/J mice and were treated with anti-BAFF monoclonal antibody (mAb) (named Sandy-2) or control IgG1 antibody. HLA.A2-specific IgG was reduced in BAFF-inhibited mice compared to the control group (Δ-13.62 vs. Δ27.07, p < 0.05). BAFF inhibition also resulted in increased pre-pro and immature B cell proportions and decreased mature B cells in the bone marrow (p < 0.05 vs. control). In the spleen, an increase in transitional B cells was observed with a significant decrease in marginal and follicular B cells (p < 0.05 vs. control). There was no significant difference in the proportions of long-lived plasma and memory B cells. Microarray analysis showed that 19 gene probes were significantly up- (>2-fold, p < 0.05) or down-regulated (≤2-fold, p < 0.05) in the BAFF-inhibited group. BAFF inhibition successfully reduced alloimmune responses through the reduction in alloantibody production and suppression of B cell differentiation and maturation. Our data suggest that BAFF suppression may serve as a useful target in desensitization therapy.

CCR5 and CXCL12 allelic variants: Possible association with childhood neuroblastoma susceptibility?

Neuroblastoma (NB) is a heterogeneous and particularly malignant childhood neoplasm in its higher stages, prone to form metastasis in selected organs and for which there is still no efficient treatment available beyond surgery. Evidence indicates that chemokines and their receptors present involvement as mediators of neuroinflammation and have a neurophysiological role. In the present study, we aimed to verify if CCR5 (rs333) and CXCL12 (rs1801157) allelic variants were associated with NB. For CCR5 (rs333) D32 carriers (OR: 5.96, IC: 2.21-16.06) and for CXCL12 genotype 3'A/3'A (OR:26.18, IC:6.15-111.4) there were statistically significant differences as well to allelic frequency (OR:4.20, IC: 2.19-8.03). Although no correlation was verified regarding prognostic parameters for both CCR5 and CXCL12 polymorphic variants, these polymorphisms may be associated with NB susceptibility which deserve attention for future investigations.

Deletion of C-C Motif Chemokine Ligand 5 Worsens Invariant Natural Killer T-Cell-Mediated Hepatitis via Compensatory Up-regulation of CXCR2-Related Chemokine Activity

BACKGROUND & AIMS

Chemokine-mediated immune cell recruitment plays pivotal roles in liver inflammation. C-C motif chemokine ligand 5 (CCL5) has been shown to be responsible for the recruitment of monocytes/macrophages and has been implicated in various liver diseases, including nonalcoholic fatty liver disease, fibrosis, and hepatocellular carcinoma. Previous studies have also shown that inhibition of CCL5 appears to be a promising therapeutic approach for several chronic liver diseases. However, whether blocking CCL5 could benefit immune cell-mediated hepatitis remains largely elusive.

METHODS

By adopting a specific agonist, alpha-galactosylceramide (α-Galcer), of invariant natural killer T cells (iNKTs), we investigated the function and mechanism of CCL5 in the iNKT induced murine hepatitis model.

RESULTS

We found significantly increased CCL5 expression in α-Galcer-induced hepatitis murine model. Such an increase in CCL5 is mainly enriched in non-parenchymal cells such as macrophages and iNKTs but not in hepatocytes. Surprisingly, CCL5 blockage by genetic deletion of Ccl5 does not affect the α-Galcer-induced iNKT activation but greatly worsens α-Galcer-induced liver injury accompanied by an increased hepatic neutrophil infiltration. Mechanistically, we demonstrated that greater neutrophil accumulation in the liver is responsible for the enhanced liver injury in Ccl5^-/- mice. Such an increased hepatic neutrophil infiltration is mainly caused by an enhanced CXCL1-CXCR2 signal in Ccl5^-/- mice. Therapeutically, either antibody-mediated neutrophil depletion or a CXCR2 antagonist, SB225002, mediated CXCR2 signaling blockage significantly ameliorated α-Galcer-induced liver injury in Ccl5^-/- mice.

CONCLUSIONS

Our present study demonstrates that (1) α-Galcer-induced murine hepatitis could greatly induce CCL5 production in macrophages and iNKT cells; (2) loss of CCL5 could enhance CXCL1 expression in hepatocytes and activate CXCL1-CXCR2 axis in neutrophils to augment their hepatic infiltration; and (3) neutrophil depletion or blockage of CXCL1-CXCR2 axis greatly improves α-Galcer-induced liver injury in Ccl5^-/- mice. This study suggests that clinical utilization of CCL5 blockage may compensatorily induce the activation of other chemokine pathways to enhance neutrophil recruitment and liver injury in hepatitis.

Inhibition of macrophage inflammatory protein-1β improves endothelial progenitor cell function and ischemia-induced angiogenesis in diabetes

Systemic inflammation might contribute to the impairment of neovasculogenesis and endothelial progenitor cell (EPC) function in clinical diabetes mellitus (DM). Macrophage inflammatory protein-1β (MIP-1β) is an inflammatory chemokine that may be up-regulated in clinical DM. Its role in diabetic vasculopathy was not clarified. This study aimed to investigate the role of MIP-1β in human EPCs and in neovasculogenesis in different diabetic animal models with hindlimb ischemia. EPCs chamber assay and in vitro tube formation assay were used to estimate the degree of EPC migration and tube formation abilities. Lepr^db/JNarl mice, C57BL/6 mice fed a high-fat diet, and streptozotocin-induced diabetic mice were used as different diabetic animal models. Laser Doppler imaging and flow cytometry were used to evaluate the degree of neovasculogenesis and the circulating levels of EPCs, respectively. MIP-1β impaired human EPC function for angiogenesis in vitro. Plasma MIP-1β levels were up-regulated in type 2 DM patients. MIP-1β inhibition enhanced the function and the C-X-C chemokine receptor type 4 expression of EPCs from type 2 diabetic patients, and improved EPC homing for ischemia-induced neovasculogenesis in different types of diabetic animals. MIP-1β directly impaired human EPC function. Inhibition of MIP-1β improved in vitro EPC function, and enhanced in vivo EPC homing and ischemia-induced neovasculogenesis, suggesting the critical role of MIP-1β for vasculopathy in the presence of DM.

Steatosis induced CCL5 contributes to early-stage liver fibrosis in nonalcoholic fatty liver disease progress

The rapidly increasing prevalence of nonalcoholic fatty liver disease (NAFLD) has become one of the major public health threats in China and worldwide. However, during the development of NAFLD, the key mechanism underlying the progression of related fibrosis remains unclear, which greatly impedes the development of optimal NAFLD therapy. In the current study, we were endeavored to characterize a proinflammatory cytokine, CCL5, as a major contributor for fibrosis in NAFLD. The results showed that CCL5 was highly expressed in fatty liver and NASH patients. In NAFLD rats induced by 8-week-HFD, CCL5 and its receptor, CCR5, were significantly up-regulated and liver fibrosis exclusively occurred in this group. In addition, we showed that hepatocytes are the major source contributing to this CCL5 elevation. Interestingly, a CCL5 inhibitor Met-CCL5, significantly decreased liver fibrosis but not hepatic steatosis. Using a cell model of hepatic steatosis, we found that the conditioned medium of lipid-overloaded hepatocytes (Fa2N-4 cells) which produced excessive CCL5 stimulated the profibrotic activities of hepatic stellate cells (LX-2) as manifested by increased migration rate, proliferation and collagen production of LX-2 cells. CCL5 knockdown in Fa2N-4 cells, Met-CCL5 or CCR5 antibody treatment on LX-2 cells all significantly inhibited the conditioned medium of FFA-treated Fa2N-4 cells to exert stimulatory effects on LX-2 cells. Consistently, the conditioned medium of Fa2N-4 cells with CCL5 over-expression significantly enhanced migration rate, cell proliferation and collagen production of LX-2 cells. All these results support that CCL5 produced by steatotic hepatocytes plays an essential role in fibrotic signaling machinery of NAFLD. In addition, we were able to identify C/EBP-β as the up-stream regulator of CCL5 gene transcription in hepatocytes treated with free fatty acid (FFA). Our data strongly supported that CCL5 plays a pivotal regulatory role in hepatic fibrosis during NAFLD, which constitutes a novel and exciting observation that may call for potential future development of specific CCL5-targeted NAFLD therapy.

Emerging role of chemokine CC motif ligand 4 related mechanisms in diabetes mellitus and cardiovascular disease: friends or foes?

Chemokines are critical components in pathology. The roles of chemokine CC motif ligand 4 (CCL4) and its receptor are associated with diabetes mellitus (DM) and atherosclerosis cardiovascular diseases. However, due to the complexity of these diseases, the specific effects of CCL4 remain unclear, although recent reports have suggested that multiple pathways are related to CCL4. In this review, we provide an overview of the role and potential mechanisms of CCL4 and one of its major receptors, fifth CC chemokine receptor (CCR5), in DM and cardiovascular diseases. CCL4-related mechanisms, including CCL4 and CCR5, might provide potential therapeutic targets in DM and/or atherosclerosis cardiovascular diseases.

Innate response activator B cells: origins and functions

Innate response activator (IRA) B cells are a subset of B-1a derived B cells that produce the growth factors granulocyte macrophage colony stimulating factor and IL-3. In mouse models of sepsis and pneumonia, B-1a B cells residing in serosal sites recognize bacteria, migrate to the spleen or lung, and differentiate to IRA B cells that then contribute to the host response by amplifying inflammation and producing polyreactive IgM. In atherosclerosis, IRA B cells accumulate in the spleen, where they promote extramedullary hematopoiesis and activate classical dendritic cells. In this review, we focus on the ontogeny and function of IRA B cells in acute and chronic inflammation.

Induced interleukin-33 expression enhances the tumorigenic activity of rat glioma cells

BACKGROUND

Glioma development is a multistep process associated with progressive genetic alterations but also regulated by cellular and noncellular components in a tumor-associated niche.

METHODS

Using 2 rat C6 glioma cell clones with different tumorigenesis, named C6-1 and C6-2, this study characterized genes associated with enhanced tumorigenic features of glioma cells by comparative cDNA microarray analysis combined with Q-PCR. Neurospehere formation and clonogenicity were examined to determine the growth of tumorigenic C6 glioma cells. The lentivirus-mediated gene knockdown approach was conducted to determine the role of interleukin-33 (IL-33) in glioma cell proliferation and migration. Transwell cell invasion assay was used to examine microglia migration induced by tumorigenic C6 cells.

RESULTS

The functional analysis of gene ontology (GO) biological processes shows that the upregulated genes found in tumorigenic C6 (C6-1) cells are closely related to cell proliferation. Tumorigenic C6 cells expressed cytokines and chemokines abundantly. Among these genes, IL-33 was profoundly induced in tumorigenic C6 cells with the expression of IL-33 receptor ST2. Furthermore, the growth rate and colony formation of tumorigenic C6 cells were attenuated by the inhibition of IL-33 and ST2 gene expression. Moreover, IL-33 was involved in tumorigenic glioma cell migration and regulation of the expression of several glioma-associated growth factors and chemokines in tumorigenic C6 cells.

CONCLUSION

Accordingly, we concluded that glioma cells with abundant production of IL-33 grow rapidly; moreover, the interactions of multiple cytokines/chemokines induced by glioma cells may develop a microenvironment that facilitates microglia/macrophage infiltration and fosters glioma growth in the brain.

Mechanisms regulating chemokine receptor activity

Co-ordinated movement and controlled positioning of leucocytes is key to the development, maintenance and proper functioning of the immune system. Chemokines and their receptors play an essential role in these events by mediating directed cell migration, often referred to as chemotaxis. The chemotactic property of these molecules is also thought to contribute to an array of pathologies where inappropriate recruitment of specific chemokine receptor-expressing leucocytes is observed, including cancer and inflammatory diseases. As a result, chemokine receptors have become major targets for therapeutic intervention, and during the past 15 years much research has been devoted to understanding the regulation of their biological activity. From these studies, processes which govern the availability of functional chemokine receptors at the cell surface have emerged as playing a central role. In this review, we summarize and discuss current knowledge on the molecular mechanisms contributing to the regulation of chemokine receptor surface expression, from gene transcription and protein degradation to post-translational modifications, multimerization, intracellular transport and cross-talk.

Importance of the CCR5-CCL5 axis for mucosal Trypanosoma cruzi protection and B cell activation

Trypanosoma cruzi is an intracellular parasite and the causative agent of Chagas disease. Previous work has shown that the chemokine receptor CCR5 plays a role in systemic T. cruzi protection. We evaluated the importance of CCR5 and CCL5 for mucosal protection against natural oral and conjunctival T. cruzi challenges. T. cruzi-immune CCR5(-/-) and wild-type C57BL/6 mice were generated by repeated infectious challenges with T. cruzi. CCR5(-/-) and wild-type mice developed equivalent levels of cellular, humoral, and protective mucosal responses. However, CCR5(-/-)-immune mice produced increased levels of CCL5 in protected gastric tissues, suggesting compensatory signaling through additional receptors. Neutralization of CCL5 in CCR5(-/-)-immune mice resulted in decreased mucosal inflammatory responses, reduced T. cruzi-specific Ab-secreting cells, and significantly less mucosal T. cruzi protection, confirming an important role for CCL5 in optimal immune control of T. cruzi replication at the point of initial mucosal invasion. To investigate further the mechanism responsible for mucosal protection mediated by CCL5-CCR5 signaling, we evaluated the effects of CCL5 on B cells. CCL5 enhanced proliferation and IgM secretion in highly purified B cells triggered by suboptimal doses of LPS. In addition, neutralization of endogenous CCL5 inhibited B cell proliferation and IgM secretion during stimulation of highly purified B cells, indicating that B cell production of CCL5 has important autocrine effects. These findings demonstrate direct effects of CCL5 on B cells, with significant implications for the development of mucosal adjuvants, and further suggest that CCL5 may be important as a general B cell coactivator.

Experimental stroke-induced changes in the bone marrow reveal complex regulation of leukocyte responses

Stroke induces a systemic response that involves rapid activation of inflammatory cascades, followed later by immunodepression. Experimental stroke-induced responses in the bone marrow, which is the primary source of circulating monocytes and granulocytes, have not been investigated previously. We show that cerebral ischaemia induced early (4  hours) release of CXCR2-positive granulocytes from the bone marrow, which was associated with rapid systemic upregulation of CXCL1 (a ligand for CXCR2) and granulocyte-colony-stimulating factor, a key cytokine involved in the mobilisation of bone marrow leukocytes. This process involves rapid activation of nuclear factor-κB and p38 mitogen-activated protein kinase in bone marrow myeloid cells. T-cell numbers in the bone marrow increased after stroke, and bone marrow cells did not show suppressed cytokine response to bacterial endotoxin stimulation in vitro. Stroke-induced laterality observed in the brain stem and in the bone marrow indicates direct involvement of the autonomic nervous system in stroke-induced cell mobilisation. We also show that systemic inflammatory changes and leukocyte responses in the bone marrow are profoundly affected by both anaesthetic and surgical stress. We conclude that stroke influences leukocyte responses in the bone marrow through multiple mechanisms and suggest that preclinical studies should take into consideration the effect of surgical manipulation in experimental models of stroke.

Genetically modified adipose tissue-derived mesenchymal stem cells overexpressing CXCR4 display increased motility, invasiveness, and homing to bone marrow of NOD/SCID mice

OBJECTIVE

This study evaluates usefulness of CXCR4 overexpression via retroviral transduction in adipose tissue-derived mesenchymal stem cells (AT-MSCs) as a strategy to increase their migration and engraftment ability.

MATERIALS AND METHODS

AT-MSCs were isolated from lipoaspirates from human healthy donors with liberase 3. Cells were transduced with retroviral vector carrying either CXCR4 or green fluorescent protein (GFP) complementary DNA, and neo-resistant colonies were selected and used in experiments. Chemotaxis, invasion through Matrigel, motor activity, gene expression, osteodifferentiation potential, and engraftment into bone marrow of nonobese diabetic/severe combined immunodeficient mice were analyzed for CXCR4-overexpressing cells and GFP-control cells.

RESULTS

Approximately 90% of retrovirus-transduced AT-MSCs expressed CXCR4 or GFP and maintained their ability to differentiate into osteocytes. CXCR4-transduced AT-MSCs displayed enhanced migration and higher invasiveness toward SDF-1 gradient. The upregulation of CXCR4 led to phosphorylation of mitogen-activated protein and AKT kinases and an increase in metalloproteinase expression after SDF-1 stimulation. The transplantation of CXCR4-transduced AT-MSCs into nonobese diabetic/severe combined immunodeficient mice led to increased engraftment into bone marrow in comparison to GFP-transduced AT-MSCs.

CONCLUSIONS

Adipose tissue is one of the alternative sources of MSCs to bone marrow. We showed that AT-MSCs overexpressing CXCR4 preserve their ability for osteodifferentiation. Enhanced migration and engraftment of the transduced AT-MSCs into bone marrow indicate the usefulness of this strategy in overcoming low engraftment of MSCs in clinical approaches of cellular therapies for bone disorders and can represent a powerful tool in regenerative medicine and gene therapies. Thus, these cells may be used as an alternative to bone marrow-derived MSCs.

CXCR4 and CCR5 ligands cooperate in monocyte and lymphocyte migration and in inhibition of dual-tropic (R5/X4) HIV-1 infection

One of the most important functions of chemokines and their receptors is the regulation of directional migration of leukocytes within tissues. In specific tissue compartments, cells are exposed to multiple chemokines presented in complex dimensional and temporal patterns. Therefore, a leukocyte requires the mechanisms to integrate the various directional signals it receives from different chemoattractants. In this study, we report that CCL3, CCL5, and CCL8, three potent mononuclear cell chemoattractants, are able to synergize with the homeostatic chemokine CXCL12 in the migration of CD14(+) monocytes, CD3(+) T-lymphocytes, or PHA-activated lymphoblasts. In addition, CCL5 augmented the CXCR4 ligand-driven ERK phosphorylation in mononuclear cells. Furthermore, the synergistic effect between CCL5 and CXCL12 in monocyte chemotaxis is inhibited in the presence of specific CCR1 antibody and AMD3100, but not by maraviroc. In HIV-1 infection assays, a combination of CXCL12 and CCL5 cooperated to inhibit the replication of the dual-tropic (R5/X4) HIV-1 HE strain. Finally, although the dual-tropic HIV-1 strain was barely suppressed by AMD3100 or maraviroc alone, HIV-1 infection was completely blocked by the combination of these two receptor antagonists. Our data demonstrate the cooperation between CCL5 and CXCL12, which has implications in migration of monocytes/lymphocytes during inflammation and in HIV-1 infection.

Anti-inflammatory effects of the GABA(B) receptor agonist baclofen in allergic contact dermatitis

The gamma amino butyric acid B (GABA(B)) receptor is a G protein-coupled receptor (GPCR) involved in synaptic transmission. Recent data indicate it to be also expressed on immune cells, along with chemokine receptors, which are also GPCRs. As GPCRs can undergo heterologous desensitization, we have examined the ability of baclofen, a GABA(B) receptor selective agonist, to interfere with the function of pro-inflammatory chemokine receptors known to be upregulated in cutaneous inflammation. In vitro, baclofen reduces chemotaxis of human peripheral blood mononuclear cells towards CCL2, CCL5, CXCL10, CXCL2 and CX3CL1 in a dose-dependant manner. Protein kinase C inhibitors calphostin C and G0 6976 could reverse this effect, pointing towards the involvement of both calcium-dependent and -independent protein kinase C in baclofen-induced inhibition of chemokine receptors. In an in vivo model of contact hypersensitivity in C57BL/6 mice, intraperitoneal injection of baclofen markedly alleviated signs of inflammation as well as recruitment of neutrophils, monocytes and lymphocytes into the skin. This study demonstrates a new role for the GABA(B) receptor in inflammation, making it a potential new therapeutic target to treat inflammatory skin diseases.

CCR5 ligands modulate CXCL12-induced chemotaxis, adhesion, and Akt phosphorylation of human cord blood CD34+ cells

CXCL12 and its receptor CXCR4 play an important role in hematopoietic stem/progenitor cell (HSPC) migration from and retention within the bone marrow. HSPCs are very selective in their chemotactic response and undergo chemotaxis only in response to CXCL12. In addition to CXCR4, HSPCs express receptors for various other chemokines; however, the role of these receptors is not well understood. Freshly isolated CD34(+) cells (highly enriched for HSPCs) from cord blood (CB) express low levels of CCR5; however, if the cells were washed with acidic buffer before Ab staining to remove any ligand bound to CCR5, then nearly 80% of CD34(+) CB cells were found to express CCR5 on the cell surface. Although none of the CCR5 ligands investigated in this study (CCL3, CCL4, and CCL5) induced chemotaxis, at relatively high concentrations they transiently enhanced CXCL12-mediated chemotaxis of CD34(+) CB cells. In contrast, CXCL12-mediated adhesion of cells to VCAM-1-coated surfaces was reduced if CD34(+) CB cells were pretreated with these CCR5 ligands for 15 min. The effect of these chemokines on CXCL12-mediated responses was not at the level of CXCR4 expression, but on downstream signaling pathways elicited by CXCL12. Pretreatment with CCR5 chemokines enhanced CXCL12-mediated Akt phosphorylation, but down-modulated calcium flux in CD34(+) CB cells. Modulation of CXCL12-mediated responses of CD34(+) cells by CCR5 chemokines provides a possible mechanism that underlies movement of HSPCs during inflammation.

Bi-directional heterologous desensitization between the major HIV-1 co-receptor CXCR4 and the kappa-opioid receptor

We previously characterized multiple interactions between chemokine and opioid G protein-coupled receptors (GPCR), and we found both mu and delta-opioid receptors cross-desensitize CCR1, CCR2, CCR5, but not CXCR4. Here we report that the kappa-opioid receptor (KOR) is able to cross-desensitize CXCR4, and this phenomenon is bi-directional. Chemotactic responses by KOR activation are diminished with prior activation of CXCR4. Additionally, calcium mobilization assays show these cross-desensitization processes occur within seconds of receptor activation, and target receptor internalization is not responsible for desensitization between these receptors. These results have implications for several essential processes including neuronal and lymphocyte development, inflammatory responses, and pain/sensitivity.

Human B cells express the orphan chemokine receptor CRAM-A/B in a maturation-stage-dependent and CCL5-modulated manner

Chemokines orchestrate the organization of leucocyte recruitment during inflammation and homeostasis. Despite growing knowledge of chemokine receptors, some orphan chemokine receptors are still not characterized. The gene CCRL2 encodes such a receptor that exists in two splice variants, CRAM-A and CRAM-B. Here, we report that CRAM is expressed by human peripheral blood and bone marrow B cells, and by different B-cell lines dependent on the B-cell maturation stage. Intriguingly, CRAM surface expression on the pre-B-cell lines Nalm6 and G2 is specifically upregulated in response to the inflammatory chemokine CCL5 (RANTES), a chemokine that is well known to play an important role in modulating immune responses. Although Nalm6 cells do not express any of the known CCL5 binding receptors, extracellular signal-regulated kinases 1 and 2 (ERK1/2) are phosphorylated upon CCL5 stimulation, suggesting a direct effect of CCL5 through the CRAM receptor. However, no calcium mobilization or migratory responses upon CCL5 stimulation are induced in B-cell lines or in transfected cells. Also, ERK1/2 phosphorylation cannot be inhibited by pertussis toxin, suggesting that CRAM does not couple to Gi proteins. Our results describe the expression of a novel, non-classical chemokine receptor on B cells that is potentially involved in immunomodulatory functions together with CCL5.

Expression of CCR5 receptors on Reed-Sternberg cells and Hodgkin lymphoma cell lines: involvement of CCL5/Rantes in tumor cell growth and microenvironmental interactions

The expression of CCL5/Rantes by Hodgkin (H) and Reed-Sternberg (RS) cells has been recently documented. In the present study we demonstrated that the CCL5 receptor (CCR5) is constitutively expressed by Hodgkin Lymphoma (HL)-derived cell lines (i.e. L-428, KM-H2, L-1236 and L-540) as shown by immunohistochemistry, flow cytometry and western blotting and also detected by immunohistochemistry on primary H-RS cells from lymph node tissues. sCD40L never significantly affected CCR5 expression, whereas a short exposure to doxorubicin down regulated its expression. CCR5 receptors on HL cell lines were functionally active, since neutralizing anti-CCL5 monoclonal antibodies inhibited basal proliferation of HL-derived cell lines and recombinant CCR5 ligands (CCL3/Mip-1 alpha, CCL4/Mip1 beta and CCL5/Rantes) increased their clonogenic growth. CCL5 secretion by L-1236, L-428 and KM-H2 cells was stimulated by CD40 engagement and also by coculturing L-1236 cells on primary stromal fibroblasts from HL-involved lymph nodes (HLF). Coculture experiments indicated that a direct contact of H-RS cells induces HLF cells to produce CCL5. Supernatants from L-1236, L-428 and KM-H2 cells stimulated migration of purified CD4+ T-cells and eosinophils in vitro. The migratory response to HL-cell lines supernatants was only partially neutralized (CD4+ cells: 70%; esinophils: 36%) by anti-CCL5 antibodies, reinforcing the notion that multiple chemokines are involved in the recruitment of nonmalignant reactive cells in HL tissues. Taken together, our results indicate a possible involvement of the CCR5/CCR5-ligands signaling in the regulation of H-RS cells growth and in the formation/maintenance of the typical tissue microenvironment of HL.

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.

Interactions between human immunodeficiency virus type 1 and vaccinia virus in human lymphoid tissue ex vivo

Vaccinia virus (VACV) has been attracting attention recently not only as a vector for various vaccines but also as an immunization tool against smallpox because of its potential use as a bioterrorism agent. It has become evident that in spite of a long history of studies of VACV, its tissue pathogenesis remains to be fully understood. Here, we investigated the pathogenesis of VACV and its interactions with human immunodeficiency virus type 1 (HIV-1) in the context of human lymphoid tissues. We found that ex vivo-cultured tonsillar tissue supports productive infection by the New York City Board of Health strain, the VACV strain of the Dryvax vaccine. VACV readily infected both T and non-T (B) lymphocytes and depleted cells of both of these subsets equally over a 12-day period postinfection. Among T lymphocytes, CD8(+) cells are preferentially depleted in accordance with their preferential infection: the probability that a CD8(+) T cell will be productively infected is almost six times higher than for a CD4(+) T cell. T cells expressing CCR5 and the activation markers CD25, CD38, and HLA-DR are other major targets for infection by VACV in lymphoid tissue. As a consequence, VACV predominantly inhibits the replication of the R5(SF162) phenotype of HIV-1 in coinfected tissues, as R5-tropic HIV-1 requires activated CCR5(+) CD4(+) cells for productive infection. Human lymphoid tissue infected ex vivo by VACV can be used to investigate interactions of VACV with other viruses, in particular HIV-1, and to evaluate various VACV vectors for the purpose of recombinant vaccine development.

Met-RANTES reduces endothelial progenitor cell homing to activated (glomerular) endothelium in vitro and in vivo

The chemokine RANTES (regulated upon activation normal T-cell expressed and secreted) is involved in the formation of an inflammatory infiltrate during glomerulonephritis. However, RANTES receptor inhibition, although reducing glomerular leukocyte infiltration, can also increase damage. We hypothesized that RANTES does not only promote the influx and activation of inflammatory leukocytes but also mediates glomerular microvascular repair by stimulating the homing of bone marrow (BM)-derived endothelial progenitor cells. To investigate the role of RANTES in the participation of BM-derived cells in glomerular vascular repair, we used a rat BM transplantation model in combination with reversible anti-Thy-1.1 glomerulonephritis. Twenty-four hours after the induction of glomerulonephritis, BM-transplanted rats were treated for 7 days with either the RANTES receptor antagonist Met-RANTES or saline. The participation of BM-derived endothelial cells in glomerular repair, glomerular monocyte infiltration, and proteinuria was evaluated at days 7 and 28. Furthermore, we used an in vitro perfusion chamber assay to study the role of RANTES receptors in shear-resistant adhesion of the CD34+ stem cells to activated endothelium under flow. In our reversible glomerulonephritis model, RANTES receptor inhibition specifically reduced the participation of BM-derived cells in glomerular vascular repair by more than 40% at day 7 without impairing monocyte influx. However, no obvious change in recovery from proteinuria or morphological damage was observed. Blockade of RANTES receptors on CD34+ cells in vitro partially inhibited platelet-enhanced, shear-resistant firm adhesion of the CD34+ cells to activated endothelium. In conclusion, our data suggest that RANTES is involved in the homing and participation of BM-derived endothelial cells in glomerular repair.

Follicular Dendritic Cell Secreted Protein (FDC-SP) Regulates Germinal Center and Antibody Responses

We previously identified follicular dendritic cell secreted protein (FDC-SP), a small secreted protein of unknown function expressed in human tonsillar germinal centers (GC). To assess potential in vivo activities of FDC-SP, transgenic mice were generated to constitutively express FDC-SP in lymphoid tissues. FDC-SP transgenic mice show relatively normal development of immune cell populations, with the exception of a small increase in mature follicular B cells, and normal lymphoid tissue architecture. Upon immunization with a T-dependent Ag, FDC-SP transgenic mice were capable of producing an Ag-specific Ab; however, the titers of Ag-specific IgG2a and IgE were significantly reduced. GC responses after immunization were markedly diminished, with transgenic mice showing decreased numbers and sizes of GCs but normal development of follicular dendritic cell networks and normal positioning of GCs. FDC-SP transgenic mice also showed reduced production of Ag-specific IgG3 Ab after immunization with a type II T-independent Ag, suggesting that the FDC-SP can also regulate the induction of B cell responses outside the GC. Purified FDC-SP transgenic B cells function normally in vitro, with the exception of blunted chemotaxis responses to CXCL12 and CXCL13. FDC-SP can induce the chemotaxis of CD40-stimulated nontransgenic B cells and can significantly enhance B cell migration in combination with chemokines, indicating that FDC-SP may function in part by regulating B cell chemotaxis. These results provide the first evidence for immunomodulatory activities of FDC-SP and implicate this molecule as a regulator of B cell responses.

Circulating mononuclear cells from euthyroid patients with thyroid-associated ophthalmopathy exhibit characteristic phenotypes

Thyroid-associated ophthalmopathy (TAO) is a common yet poorly understood component of Graves' disease involving inflammation, congestion and soft tissue remodelling of the orbit. Unlike most autoimmune disorders, TAO has variable severity but follows a predictable course and is usually self-limited. The objective of this study was to investigate the phenotypic profile of peripheral blood mononuclear cells in euthyroid patients with TAO. The study was a prospective, consecutive analysis of the peripheral blood mononuclear cell phenotype in patients with TAO and normal controls. We demonstrate that the fraction of T cells expressing CD69, CD25 or CXCR4 is significantly greater in patients with TAO compared to control donors. In addition, the fraction of CD19(+) CD25(+) B cells is significantly greater. We did not find differences between the two groups of subjects in monocytes expressing these markers. There is a phenotypic shift in peripheral blood lymphocytes associated with TAO that appears durable and persists beyond the hyperthyroid phase of Graves' disease. These changes may support the immune reaction provoking orbital disease development.

Antibodies to Stem Cell Marker Antigens Reduce Engraftment of Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) have enormous potential for use in transplantation and gene therapy. However, the frequency of repopulating HSCs is often very low; thus, highly effective techniques for cell enrichment and maintenance are required to obtain sufficient cell numbers for therapeutic use and for studies of HSC physiology. Common methods of HSC enrichment use antibodies recognizing HSC surface marker antigens. Because antibodies are known to alter the physiology of other cell types, we investigated the effect of such enrichment strategies on the physiology and lineage commitment of HSCs. We sorted HSCs using a method that does not require antibodies: exclusion of Hoechst 33342 to isolate side population (SP) cells. To elucidate the effect of antibody binding on this HSC population, we compared untreated SP cells with SP cells treated with the Sca-1(+)c-Kit(+)Lin(-) (SKL) antibody cocktail prior to SP sorting. Our findings revealed that HSCs incubated with the antibody cocktail had decreased expression of the stem cell-associated genes c-Kit, Cd34, Tal-1, and Slamf1 relative to untreated SP cells or to cells treated with polyclonal isotype control antibodies. Moreover, SKL antibodies induced cycling in SP cells and diminished their ability to confer long-term hematopoietic engraftment in lethally irradiated mice. Taken together, these data suggest that antibody-based stem cell isolation procedures can have negative effects on HSC physiology.

Neuronal apoptotic signaling pathways probed and intervened by synthetically and modularly modified (SMM) chemokines

As the main coreceptors for human immunodeficiency virus type 1 (HIV-1) entry, CXCR4 and CCR5 play important roles in HIV-associated dementia (HAD). HIV-1 glycoprotein gp120 contributes to HAD by causing neuronal damage and death, either directly by triggering apoptotic pathways or indirectly by stimulating glial cells to release neurotoxins. Here, to understand the mechanism of CXCR4 or CCR5 signaling in neuronal apoptosis associated with HAD, we have applied synthetically and modularly modified (SMM)-chemokine analogs derived from natural stromal cell-derived factor-1alpha or viral macrophage inflammatory protein-II as chemical probes of the mechanism(s) whereby these SMM-chemokines prevent or promote neuronal apoptosis. We show that inherently neurotoxic natural ligands of CXCR4, such as stromal cell-derived factor-1alpha or viral macrophage inflammatory protein-II, can be modified to protect neurons from apoptosis induced by CXCR4-preferring gp120(IIIB), and that the inhibition of CCR5 by antagonist SMM-chemokines, unlike neuroprotective CCR5 natural ligands, leads to neurotoxicity by activating a p38 mitogen-activated protein kinase (MAPK)-dependent pathway. Furthermore, we discover distinct signaling pathways activated by different chemokine ligands that are either natural agonists or synthetic antagonists, thus demonstrating a chemical biology strategy of using chemically engineered inhibitors of chemokine receptors to study the signaling mechanism of neuronal apoptosis and survival.

HIV-1 coreceptors CCR5 and CXCR4 both mediate neuronal cell death but CCR5 paradoxically can also contribute to protection

The chemokine receptors CCR5 and CXCR4 serve, in addition to CD4, as coreceptors for human immunodeficiency virus-1 (HIV-1), and infection with HIV-1 can cause dementia. In brain-derived cells, HIV-1 envelope glycoprotein gp120 initiates a signaling cascade that involves p38 mitogen-activated protein kinase and leads to neuronal cell death. Using mixed neuronal/glial cultures from rats and mice genetically deficient in one or both HIV coreceptors, we show here that CCR5, CXCR4 or both can mediate HIV/gp120 neurotoxicity depending on the viral strain. Paradoxically, we also found evidence for a CCR5-mediated neuroprotective pathway. We identify protein kinase Akt/PKB as an essential component of this pathway, which can be triggered by the CCR5 agonists macrophage inflammatory protein-1beta and regulated-and-normal-T-cell-expressed-and-secreted. Moreover, these CCR5 ligands prevent neuronal cell death induced by stromal cell-derived factor-1, a CXCR4 agonist. Both neurons and glia coexpress CXCR4 and CCR5. Ca2+ imaging experiments demonstrate that engagement of CCR5 prevents CXCR4-triggered increases in intracellular free Ca2+. This finding suggests that CCR5 ligands can protect neurons at least, in part, by modulating CXCR4-mediated toxicity through heterologous desensitization.

CXCR4 and CCR5 mediate homing of primitive bone marrow-derived hematopoietic cells to the postnatal thymus

Factors governing the entry of cells into the postnatal thymus are poorly understood. We aimed to define molecular mechanisms mediating the homing of bone marrow cells to the thymus using a sublethally irradiated in vivo murine model. Entry of unfractionated and lineage-depleted bone marrow cells to the thymus, but not bone marrow, was a Galphai-mediated phenomenon. Lineage-depleted cells that had homed to the thymus expressed abundant CXCR4 and CCR5 mRNA, alone of 17 chemokine receptors evaluated by QPCR. Thymic-homed cells were distinct from cells that had homed to bone marrow in expression of CXCR4 and CCR5 by mRNA quantification and cell-surface expression of protein. Abrogation of CXCR4 and CCR5 function by genetic, antibody, or pharmacologic means impaired homing of lineage-depleted cells to the thymus, although not in a synergistic manner, implying interdependency of these receptors in the homing process. Competitive repopulation experiments demonstrated that inhibiting CXCR4-mediated homing adversely affected the double-negative cell pool at 2 weeks, suggesting that cells with prothymocytic activity may in part home via CXCR4. Overall, our data demonstrate differential homing mechanisms governing entry of unfractionated and lineage-depleted cells to irradiated bone marrow or thymus, with thymic homing of immature cells being pertussis-sensitive and mediated by the chemokine receptors CXCR4 and CCR5.

Murine B16 Melanomas Expressing High Levels of the Chemokine Stromal-Derived Factor-1/CXCL12 Induce Tumor-Specific T Cell Chemorepulsion and Escape from Immune Control

The chemokine, stromal-derived factor-1/CXCL12, is expressed by normal and neoplastic tissues and is involved in tumor growth, metastasis, and modulation of tumor immunity. T cell-mediated tumor immunity depends on the migration and colocalization of CTL with tumor cells, a process regulated by chemokines and adhesion molecules. It has been demonstrated that T cells are repelled by high concentrations of the chemokine CXCL12 via a concentration-dependent and CXCR4 receptor-mediated mechanism, termed chemorepulsion or fugetaxis. We proposed that repulsion of tumor Ag-specific T cells from a tumor expressing high levels of CXCL12 allows the tumor to evade immune control. Murine B16/OVA melanoma cells (H2b) were engineered to constitutively express CXCL12. Immunization of C57BL/6 mice with B16/OVA cells lead to destruction of B16/OVA tumors expressing no or low levels of CXCL12 but not tumors expressing high levels of the chemokine. Early recruitment of adoptively transferred OVA-specific CTL into B16/OVA tumors expressing high levels of CXCL12 was significantly reduced in comparison to B16/OVA tumors, and this reduction was reversed when tumor-specific CTLs were pretreated with the specific CXCR4 antagonist, AMD3100. Memory OVA-specific CD8+ T cells demonstrated antitumor activity against B16/OVA tumors but not B16/OVA.CXCL12-high tumors. Expression of high levels of CXCL12 by B16/OVA cells significantly reduced CTL colocalization with and killing of target cells in vitro in a CXCR4-dependent manner. The repulsion of tumor Ag-specific T cells away from melanomas expressing CXCL12 confirms the chemorepellent activity of high concentrations of CXCL12 and may represent a novel mechanism by which certain tumors evade the immune system.

Chemokine receptor expression and function in childhood acute lymphoblastic leukemia of B-lineage

Scanty information is available on chemokine receptor expression and function in childhood B-lineage acute lymphoblastic leukemia (ALL). Thirteen pro-B, 17 early pre-B, 12 pre-B, and 9 B-ALL/Burkitt lymphoma (BL) pediatric cases were tested for CXCR1 to CXCR5 and CCR1 to CCR7 expression. CXCR2, CXCR3, and CXCR4 were expressed in the majority of cases, while the other receptors were variably expressed or absent. CXCR4 mediated chemotaxis of all leukemic cell subtypes. Freshly isolated CCR7(+) early pre-B-ALL cells migrated to CCL19, whereas CCR7(+) pro-B- and pre-B-ALL cells were attracted by CCL19 only following culture with soluble recombinant CD40 ligand.

Trafficking of normal stem cells and metastasis of cancer stem cells involve similar mechanisms: pivotal role of the SDF-1-CXCR4 axis

The alpha-chemokine stromal-derived factor (SDF)-1 and the G-protein-coupled seven-span transmembrane receptor CXCR4 axis regulates the trafficking of various cell types. In this review, we present the concept that the SDF-1-CXCR4 axis is a master regulator of trafficking of both normal and cancer stem cells. Supporting this is growing evidence that SDF-1 plays a pivotal role in the regulation of trafficking of normal hematopoietic stem cells (HSCs) and their homing/retention in bone marrow. Moreover, functional CXCR4 is also expressed on nonhematopoietic tissue-committed stem/progenitor cells (TCSCs); hence, the SDF-1-CXCR4 axis emerges as a pivotal regulator of trafficking of various types of stem cells in the body. Furthermore, because most if not all malignancies originate in the stem/progenitor cell compartment, cancer stem cells also express CXCR4 on their surface and, as a result, the SDF-1-CXCR4 axis is also involved in directing their trafficking/metastasis to organs that highly express SDF-1 (e.g., lymph nodes, lungs, liver, and bones). Hence, we postulate that the metastasis of cancer stem cells and trafficking of normal stem cells involve similar mechanisms, and we discuss here the common molecular mechanisms involved in these processes. Finally, the responsiveness of CXCR4+ normal and malignant stem cells to an SDF-1 gradient may be regulated positively/primed by several small molecules related to inflammation which enhance incorporation of CXCR4 into membrane lipid rafts, or may be inhibited/blocked by small CXCR4 antagonist peptides. Consequently, strategies aimed at modulating the SDF-1-CXCR4 axis could have important clinical applications both in regenerative medicine to deliver normal stem cells to the tissues/organs and in clinical hematology/oncology to inhibit metastasis of cancer stem cells.

CXC chemokine ligand 12-induced focal adhesion kinase activation and segregation into membrane domains is modulated by regulator of G protein signaling 1 in pro-B cells

CXCL12-induced chemotaxis and adhesion to VCAM-1 decrease as B cells differentiate in the bone marrow. However, the mechanisms that regulate CXCL12/CXCR4-mediated signaling are poorly understood. We report that after CXCL12 stimulation of progenitor B cells, focal adhesion kinase (FAK) and PI3K are inducibly recruited to raft-associated membrane domains. After CXCL12 stimulation, phosphorylated FAK is also localized in membrane domains. The CXCL12/CXCR4-FAK pathway is membrane cholesterol dependent and impaired by metabolic inhibitors of G(i), Src family, and the GTPase-activating protein, regulator of G protein signaling 1 (RGS1). In the bone marrow, RGS1 mRNA expression is low in progenitor B cells and high in mature B cells, implying developmental regulation of CXCL12/CXCR4 signaling by RGS1. CXCL12-induced chemotaxis and adhesion are impaired when FAK recruitment and phosphorylation are inhibited by either membrane cholesterol depletion or overexpression of RGS1 in progenitor B cells. We conclude that the recruitment of signaling molecules to specific membrane domains plays an important role in CXCL12/CXCR4-induced cellular responses.

HIV-1 entry inhibitors: closing the front door

Highly active antiretroviral therapy (HAART) has led to major declines in morbidity and mortality of HIV-1-infected individuals, but the increasing prevalence of drug-resistant viral isolates, combined with the toxicity and other limitations of current treatments, make the development of new therapies a high priority. As knowledge of viral entry has expanded, this step of the viral life cycle has become a target for novel therapeutic strategies. An emerging group of antiretrovirals, known collectively as entry inhibitors, targets several distinct steps in viral entry including CD4 binding, chemokine receptor engagement and the structural changes in the viral envelope required for fusion between viral and cellular membranes. Many entry inhibitors are in various stages of clinical development, with one already licensed for use. This review will provide an overview of the mechanisms involved in the entry process, highlight promising entry blockers under development and discuss several considerations related to treatment that are unique to this class of antiretroviral drugs.

Leukocyte migration and graft-versus-host disease

Graft-versus-host disease (GVHD) remains a significant complication of allogeneic bone marrow transplantation (allo-BMT). Acute GVHD is mediated by immunocompetent donor T cells, which migrate to lymphoid tissues soon after infusion, recognize host alloantigens, and become activated upon interaction with host antigen-presenting cells (APCs). Recent work from our group and others suggests that activated effector T cells exit lymphoid tissues and traffic to mucosal sites and parenchymal target organs such as the gastrointestinal (GI) tract, liver, lung, and skin where they cause tissue damage. The molecular interactions necessary for effector cell migration during GVHD have become the focus of a growing body of research, as these interactions represent potential therapeutic targets. In this review we discuss chemokine and chemokine receptor interactions and adhesion molecules that have been shown to play roles in effector cell migration in experimental GVHD models, and we discuss a potential model for the role of chemokines during the activation phase of GVHD.

Incorporation of CXCR4 into membrane lipid rafts primes homing-related responses of hematopoietic stem/progenitor cells to an SDF-1 gradient

We found that supernatants of leukapheresis products (SLPs) of patients mobilized with granulocyte–colony-stimulating factor (G-CSF) or the various components of SLPs (fibrinogen, fibronectin, soluble vascular cell adhesion molecule-1 [VCAM-1], intercellular adhesion molecule-1 [ICAM-1], and urokinase plasminogen activator receptor [uPAR]) increase the chemotactic responses of hematopoietic stem/progenitor cells (HSPCs) to stromal-derived factor-1 (SDF-1). However, alone they do not chemoattract HSPCs, but they do increase or prime the cells' chemotactic responses to a low or threshold dose of SDF-1. We observed that SLPs increased calcium flux, phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 and AKT, secretion of matrix metalloproteinases, and adhesion to endothelium in CD34+ cells. Furthermore, SLPs increased SDF-dependent actin polymerization and significantly enhanced the homing of human cord blood (CB)– and bone marrow (BM)–derived CD34+ cells in a NOD/SCID mouse transplantation model. Moreover, the sensitization or priming of cell chemotaxis to an SDF-1 gradient was dependent on cholesterol content in the cell membrane and on the incorporation of the SDF-1 binding receptor CXCR4 and the small GTPase Rac-1 into membrane lipid rafts. This colocalization of CXCR4 and Rac-1 in lipid rafts facilitated guanosine triphosphate (GTP) binding/activation of Rac-1. Hence, we postulate that CXCR4 could be primed by various factors related to leukapheresis and mobilization that increase its association with membrane lipid rafts, allowing the HSPCs to better sense the SDF-1 gradient. This may partially explain why HSPCs from mobilized peripheral blood leukapheresis products engraft more quickly in patients than do those from BM or CB. Based on our findings, we suggest that the homing of HSPCs is optimal when CXCR4 is incorporated in membrane lipid rafts and that ex vivo priming of HSPCs with some of the SLP-related molecules before transplantation could increase their engraftment.

Transplantation studies in C3-deficient animals reveal a novel role of the third complement component (C3) in engraftment of bone marrow cells

Mice deficient in complement C3 (C3(-/-)) are hematologically normal under steady-state conditions, and yet displayed a significant delay in hematopoietic recovery from either irradiation or transplantation of wild-type (WT) hematopoietic stem/progenitor cells (HSPC). Transplantation of histocompatible WT Sca-1(+) cells into C3(-/-) mice resulted in a (i) decrease in day 12 CFU-S, (ii) 5-7-day delay in platelet and leukocyte recovery, and (iii) reduced number of BM CFU-GM progenitors at day 16 after transplantation. Nevertheless, HSPC from C3(-/-) mice engrafted normally into irradiated WT mice, suggesting that there was a defect in the hematopoietic environment of C3(-/-) mice. Since C3(-/-) mice cannot activate/cleave C3, the C3 fragments C3a, C3a(des-Arg), and iC3b were examined for a role in HSPC engraftment. Liquid-phase C3a and C3a(des-Arg) increased CXCR4 incorporation into membrane lipid rafts (thus potentiating HSPC responses to SDF-1 gradients), whereas iC3b was deposited onto irradiated BM cells and functioned to tether CR3(CD11b/CD18)(+)HSPC to damaged stroma. The activity of C3a(des-Arg) suggested that C3aR(+)HSPC also expressed the C5L2 (receptor for C3a and C3a(des-Arg)) and this was confirmed. In conclusion, a novel mechanism for HSC engraftment was identified, which involves complement activation and specific C3 fragments that promote conditioning for transplantation and enhance HSPC engraftment.

Expression of the chemokine receptor CCR2 on immature B cells negatively regulates their cytoskeletal rearrangement and migration

Immature B cells are targeted to specific areas in the spleen, where a fraction of these cells receive signals that induce them to mature and participate in the immune response. In this study, we show that the C-C chemokine receptor 2 (CCR2) is transcribed in immature B cells, while its message is dramatically down-regulated at the mature stage. CCR2-deficient cells exhibit up-regulation of chemokine-induced actin polymerization, migration, and homing to the lymph nodes of immature B cells. In addition, we demonstrate that control of homing by CCR2 is mediated by its ligand, CCL2/JE, which is secreted by B cells and down-regulates the stromal derived factor-1 (SDF-1) signaling cascade. Thus, this study describes an additional, previously uncharacterized, role for CCR2 and its ligand as negative regulators of the homing of immature B cells.

Differential Roles for CCR5 Expression on Donor T Cells during Graft-versus-Host Disease Based on Pretransplant Conditioning

The coordinated expression of chemokines and receptors may be important in the directed migration of alloreactive T cells during graft-vs-host disease (GVHD). Recent work demonstrated in a murine model that transfer of CCR5-deficient (CCR5(-/-)) donor cells to nonconditioned haploidentical recipients resulted in reduced donor cell infiltration in liver and lymphoid tissues compared with transfer of CCR5(+/+) cells. To investigate the function of CCR5 during GVHD in conditioned transplant recipients, we transferred CCR5(-/-) or wild-type C57BL/6 (B6) T cells to lethally irradiated B6D2 recipients. Unexpectedly, we found an earlier time to onset and a worsening of GVHD using CCR5(-/-) T cells, which was associated with significant increases in the accumulation of alloreactive CD4(+) and CD8(+) T cells in liver and lung. Conversely, the transfer of CCR5(-/-) donor cells to nonirradiated recipients led to reduced infiltration of target organs, confirming previous studies and demonstrating that the role of CCR5 on donor T cells is dependent on conditioning of recipients. Expression of proinflammatory chemokines in target tissues was dependent on conditioning of recipients, such that CXCL10 and CXCL11 were most highly expressed in tissues of irradiated recipients during the first week post-transplant. CCR5(-/-) T cells were shown to have enhanced migration to CXCL10, and blocking this ligand in vivo improved survival in irradiated recipients receiving CCR5(-/-) T cells. Our data indicate that the effects of inhibiting CCR5/ligand interaction on donor T cells during GVHD differ depending on conditioning of recipients, a finding with potentially important clinical significance.

CCL19 and CXCL12 Trigger in Vitro Chemotaxis of Human Mantle Cell Lymphoma B Cells

PURPOSE

Few data are available in the literature on chemokine receptor expression and migratory capability of mantle cell lymphoma (MCL) B cells. Information on these issues may allow us to identify novel mechanisms of chemokine-driven tumor cell migration.

EXPERIMENTAL DESIGN

The research was designed to investigate: (a) expression of CCR1 to CCR7 and CXCR1 to CXCR5 chemokine receptors; and (b) chemotaxis to the respective ligands in MCL B cells and in their normal counterparts, i.e., CD5+ B cells.

RESULTS

Malignant B cells from MCL patients and normal counterparts displayed similar chemokine receptor profiles. MCL B cells were induced to migrate by CXCL12 and CCL19, whereas normal CD5+ B cells migrated to the former, but not the latter chemokine. Overnight culture of MCL B cells and their normal counterparts with CXCL12 cross-sensitized other chemokine receptors to their ligands in some tumor samples but not in CD5+ B cells.

CONCLUSIONS

CCR7 and CXCR4 ligands may play a key role in tumor cell migration and spreading in vivo. CXCL12 may additionally contribute by sensitizing MCL B cells to respond to the ligands of other chemokine receptors.

Co-receptor antagonists as HIV-1 entry inhibitors

PURPOSE OF REVIEW

A new mechanistic understanding of how HIV-1 enters cells has emerged recently, and these discoveries are now being translated into novel therapeutic agents. Along with CD4, HIV-1 requires a chemokine receptor, CCR5 or CXCR4, as an entry co-receptor, and differential co-receptor selectivity is an important determinant of viral diversity and pathogenesis. CCR5 and CXCR4 blockers have been the focus of much research and are now entering clinical trials.

RECENT FINDINGS

Several CCR5 antagonists with anti-HIV-1 activity have been developed, including small-molecule agents, monoclonal antibodies and modified chemokines. At least four small-molecule and one antibody CCR5 inhibitor are in various stages of preclinical and clinical testing. Most or all infected individuals harbor CCR5-using variants, and promising findings have been reported from very preliminary clinical studies. CXCR4 antagonists under development include small-molecule and short-peptide inhibitors. Only a subset of late-stage individuals harbor CXCR4-using strains, and early clinical studies of CXCR4 inhibition showed some evidence of suppression in certain individuals.

SUMMARY

Chemokine receptor antagonists offer great promise as a much-needed new class of antiviral agent. They also raise questions that are unique to agents targeting these cellular receptors, including whether drug resistance will lead to variants with altered co-receptor selectivity, the tolerability of chronically blocking receptors involved in inflammation (CCR5, CXCR4) or essential in development and hematopoesis (CXCR4), and the role of co-receptor phenotyping in selecting blocking agents. In addition to HIV-1 infection, these drugs may also have utility in inflammation, cancer, stem cell transplant and other areas.

Differential response of platelets to chemokines: RANTES non-competitively inhibits stimulatory effect of SDF-1 alpha

BACKGROUND

Among the chemokines related to CXC and CC receptor groups and released from platelets, leukocytes and endothelial cells, SDF-1, TARC and MDC have been found to be platelet agonists. Platelets do not contain SDF-1 alpha. In contrast, RANTES is constitutively present in platelet alpha-granules and released upon platelet activation.

OBJECTIVES

To study a possible role of RANTES as a modulator of SDF-1 alpha effect on platelets, in relation to CXCR4 and various CC receptors.

METHODS

CXCR-4 (CXCL12) receptor expression and platelet activation were evaluated by flow cytometry, platelet deposition was studied by cone and plate(let) analyzer, and platelet aggregation by turbidometric aggregometry.

RESULTS

Flow cytometry studies revealed similar expression of CXCR-4, the specific receptor of SDF-1 alpha on intact, inactivated, and activated platelets. Preincubation of platelets with RANTES affected neither CXCR-4 expression, nor SDF-1 alpha binding to the platelet membrane. In the presence of fibrinogen, SDF-1 alpha activated gel-filtered platelets. RANTES did not activate platelets, but substantially (by 70%) inhibited SDF-1 alpha-induced fibrinogen binding. Similarly, RANTES abrogated the promoting effect of SDF-1 alpha on whole blood platelet adhesion to endothelial cell monolayer under venous flow conditions. In platelet-rich plasma, RANTES moderately inhibited SDF-1 alpha-induced platelet aggregation, while it did not affect aggregation induced by thrombin-receptor activation peptide, adenosine diphosphate, or phorbol 12-myristate 13-acetate. A synergistic inhibitory effect of RANTES and prostaglandin E1 used at subthreshold concentrations, on SDF-1 alpha-induced aggregation and SDF-1 alpha-induced fibrinogen binding to platelets was observed, which may suggest involvement of RANTES in a cAMP-dependent signal transduction pathway.

CONCLUSIONS

RANTES non-competitively inhibits activation of platelets by SDF-1 alpha, and thus may play a regulatory role in platelet response to inflammation.

Chemokines acting via CXCR2 and CXCR4 control the release of neutrophils from the bone marrow and their return following senescence

In this study we provide evidence that the SDF-1alpha/CXCR4 chemokine axis is involved in both the retention of neutrophils within the bone marrow and the homing of senescent neutrophils back to the bone marrow. We show that the functional responses of freshly isolated human and murine neutrophils to CXCR2 chemokines are significantly attenuated by SDF-1alpha, acting via CXCR4. As a consequence, the mobilization of neutrophils from the bone marrow in vivo by the CXCR2-chemokine, KC, was dramatically enhanced by blocking the effects of endogenous SDF-1alpha using a specific CXCR4 antagonist. As neutrophils age, they upregulate expression of CXCR4 and acquire the ability to migrate toward SDF-1alpha. We show here that these senescent CXCR4(high) neutrophils preferentially home to the bone marrow in vivo in a CXCR4-dependent manner, suggesting a previously undefined mechanism for the clearance of senescent neutrophils from the circulation.

CXCR4 and SDF-1 expression in B-cell chronic lymphocytic leukemia and stage of the disease

The pathogenesis of B-cell chronic lymphocytic leukemia (B-CLL) has been linked to an overexpression of the chemokine receptor CXCR4 and increased in vitro functional response to its natural ligand CXCL12 (SDF-1). The CXCR4/SDF-1 system appears to be important for tissue localization and increased survival of B-CLL cells. The aim of our study was to examine if CXCR4 expression and SDF-1 blood levels were correlated to clinical and pathological stage of B-CLL. Flow cytometry and enzyme-linked immunosorbent assay (ELISA) techniques were used to determine CXCR4 expression and SDF-1 plasma levels, respectively, in a cohort of 51 patients diagnosed with B-CLL to correlate these measurements with several parameters that define the clinical stage of the disease. We confirmed that CXCR4 was consistently expressed on circulating B-CLL cells with a fluorescence intensity that was five-fold greater than in cells from healthy volunteers. There was a correlation between CXCR4 expression and leukocyte count ( r: 0.55, p<0.01), and CD19(+)/CD5(+ )cells ( r: 0.63, p<0.01). Interestingly, the group of B-CLL patients showed lower SDF-1 plasma levels compared to the control group. However, there was no correlation between CXCR4 or SDF-1 expression and the clinical stage of disease or the pattern of bone marrow infiltration. The results obtained suggest that other factors, and not only alteration in the SDF-1/CXCR4 chemokine system, must account for marrow infiltration of neoplastic cells observed in B-CLL and that CXCR4 could be involved in other features that exhibit malignant B cells, such as increased survival, rather than in their homing or migration to the bone marrow.

Functional receptor for C3a anaphylatoxin is expressed by normal hematopoietic stem/progenitor cells, and C3a enhances their homing-related responses to SDF-1

Complement has recently been implicated in developmental pathways and noninflammatory processes. The expression of various complement components and receptors has been shown in a wide range of circulating myeloid and lymphoid cells, but their role in normal hematopoiesis and stem cell homing has not yet been investigated. We report that normal human CD34(+) cells and lineage-differentiated hematopoietic progenitors express the complement anaphylatoxin C3a receptor (C3aR) and respond to C3a. Moreover, C3a, but not the biologically inactive desArg-C3a, induces calcium flux in these cells. Furthermore, we found that C3 is secreted by bone marrow stroma and that, although C3a does not influence directly the proliferation/survival of hematopoietic progenitors, it (1) potentiates the stromal cell-derived factor 1 (SDF-1)-dependent chemotaxis of human CD34(+) cells and lineage-committed myeloid, erythroid, and megakaryocytic progenitors; (2) primes SDF-1-dependent trans-Matrigel migration; and (3) stimulates matrix metalloproteinase-9 secretion and very late antigen 4 (VLA-4)-mediated adhesion to vascular cell adhesion molecule 1 (VCAM-1). Furthermore, we found that murine Sca-1(+) cells primed by C3a engrafted faster in lethally irradiated animals. These results indicate that normal human hematopoietic stem and progenitor cells express functional C3aR and that the C3aR-C3a axis sensitizes the responses of these cells to SDF-1 and thus may be involved in promoting their homing into the bone marrow via cross talk with the SDF-CXC chemokine receptor-4 (CXCR4) signaling axis. C3a is the first positive regulator of this axis to be identified.