B lymphocyte chemotaxis regulated in association with microanatomic localization, differentiation state, and B cell receptor engagement

BAFF enhances chemotaxis of primary human B cells: a particular synergy between BAFF and CXCL13 on memory B cells

B-cell-activating factor of the TNF family, (BAFF), and a proliferation-inducing ligand (APRIL) regulate B-lymphocyte survival and activation. We report that BAFF, but not APRIL, increased the chemotactic response of primary human B cells to CCL21, CXCL12, and CXCL13. The BAFF-induced increase in B-cell chemotaxis was totally abolished by blockade of BAFF-R and was strongly dependent on the activation of PI3K/AKT, NF-kappaB, and p38MAPK pathways. BAFF had similar effects on the chemotaxis of naive and memory B cells in response to CCL21 but increased more strongly that of memory B cells to CXCL13 than that of naive B cells. Our findings indicate a previously unreported role for the BAFF/BAFF-R pair in mature B-cell chemotaxis. The synergy between CXCL13 and BAFF produced by stromal cells and follicular dendritic cells may have important implications for B-cell homeostasis, the development of normal B-cell areas, and for the formation of germinal center-like follicles that may be observed in various autoimmune diseases.

Differential regulation of hypoxia-induced CXCR4 triggering during B-cell development and lymphomagenesis

The chemokine receptor CXCR4 plays a central role in organ-specific homing and tumor spreading and is induced by hypoxia. B lymphocytes are exposed to low oxygen tensions during their development, but the influence of hypoxia on their physiology is poorly understood. Here, we show that hypoxia is associated with up-regulation of CXCR4 expression in human normal and malignant B cells, through both transcriptional and posttranslational mechanisms. However, a dichotomic functional response to CXCR4 triggering was observed: both peripheral B cells and lymphomas arising from mature B cells displayed increased responses to CXCR4 triggering under hypoxia, whereas germinal center (GC) B cells as well as GC-derived lymphomas showed CXCR4 receptor desensitization. This phenomenon was associated with differential modulation of key signal-transducing molecules, including mitogen-activated protein kinase phosphatase-1 and regulator of G protein signaling molecule-1. The unresponsiveness of GC-derived lymphomatous B cells to CXCR4 triggering under hypoxia may have implications for the development and pathogenesis of GC-derived lymphoid tumors.

Cutting Edge: Acute and chronic exposure of immature B cells to antigen leads to impaired homing and SHIP1-dependent reduction in stromal cell-derived factor-1 responsiveness

An encounter of B cells with cognate self Ags in the periphery can lead to anergy, a condition characterized by altered anatomical localization, shortened life span, and refractility to Ag stimulation. We recently reported that an immature B cell encounter with cognate self-Ag in the bone marrow can also lead to anergy. In this study we show that anergic as well as acutely Ag-stimulated immature B cells are defective in stromal cell-derived factor-1 (SDF-1)-induced calcium mobilization and migration and do not localize to bone marrow following adoptive transfer. This hyporesponsiveness does not involve CXCR4 modulation. However, BCR signal-mediated hyporesponsiveness to SDF-1 is associated with phosphorylation of the 5-inositol phosphatase SHIP1 and requires SHIP1 expression. Therefore, an encounter with cognate Ag may, by preventing SDF-1-induced phosphatidylinositol 3,4,5-triphosphate accumulation, trigger premature emigration of immature B cells from bone marrow.

Analysis of antigen-stimulated B cell migration into germinal centers during the early stage of a T-dependent immune response

The quasimonoclonal (QM) mouse provides a model to analyze B cell selection because major B cell antigen receptors (BCR) are composed of the knockin V(H)DJ(H) 17.2.25 (V(H)T) encoded H chain and the lambda1 or lambda2 L chain, thereby being specific for (4-hydoxy-3-nitrophenyl)acetyl (NP). We have reported that during a T-dependent antibody (Ab) response for a low-affinity NP analog p-nitrophenylacetyl (pNP), although V(H)T/lambda1 and V(H)T/lambda2 IgM were equally produced, V(H)T/lambda2 IgG almost exclusively underwent affinity maturation toward pNP. The initial affinity of V(H)T/lambda2 B cells for pNP was approximately 50-100-fold higher than that of V(H)T/lambda1 B cells, suggesting a role of BCR affinity in recruiting B cells to affinity maturation processes. Here, we investigated whether the intensity of BCR signals could contribute to the selection of V(H)T/lambda2 B cells for affinity maturation. V(H)T/lambda2 B cells were more responsive to pNP than V(H)T/lambda1 B cells in vitro. When CFSE-labeled QM B cells were transferred into the wild type mice where T cells had been primed with chicken gamma-globulin (CGG), QM B cells challenged by pNP-conjugated CGG could be observed to get activated and migrate to GCs in the early phase of the T-dependent response to pNP-CGG. Adoptive transfer of sorted populations revealed that the V(H)T/lambda2 B cell population was more potent in migration into GCs than the V(H)T/lambda1 counterpart. Thus, it is suggested that the higher BCR affinity of V(H)T/lambda2 B cells may be an initial cue for their recruitment to GCs during a T-dependent Ab response.

Blocking CXCR4-mediated cyclic AMP suppression inhibits brain tumor growth in vivo

The chemokine CXCL12 and its cognate receptor CXCR4 regulate malignant brain tumor growth and are potential chemotherapeutic targets. However, the molecular basis for CXCL12-induced tumor growth remains unclear, and the optimal approach to inhibiting CXCR4 function in cancer is unknown. To develop such a therapeutic approach, we investigated the signaling pathways critical for CXCL12 function in normal and malignant cells. We discovered that CXCL12-dependent tumor growth is dependent upon sustained inhibition of cyclic AMP (cAMP) production, and that the antitumor activity of the specific CXCR4 antagonist AMD 3465 is associated with blocking cAMP suppression. Consistent with these findings, we show that pharmacologic elevation of cAMP with the phosphodiesterase inhibitor Rolipram suppresses tumor cell growth in vitro and, upon oral administration, inhibits intracranial growth in xenograft models of malignant brain tumors with comparable efficacy to AMD 3465. These data indicate that the clinical evaluation of phosphodiesterase inhibitors in the treatment of patients with brain tumors is warranted.

Interaction of mature CD3+CD4+ T cells with dendritic cells triggers the development of tertiary lymphoid structures in the thyroid

Ectopic expression of CC chemokine ligand 21 (CCL21) in the thyroid leads to development of lymphoid structures that resemble those observed in Hashimoto thyroiditis. Deletion of the inhibitor of differentiation 2 (Id2) gene, essential for generation of CD3-CD4+ lymphoid tissue-inducer (LTi) cells and development of secondary lymphoid organs, did not affect formation of tertiary lymphoid structures. Rather, mature CD3+CD4+ T cells were critical for the development of tertiary lymphoid structures. The initial stages of this process involved interaction of CD3+CD4+ T cells with DCs, the appearance of peripheral-node addressin-positive (PNAd+) vessels, and production of chemokines that recruit lymphocytes and DCs. These findings indicate that the formation of tertiary lymphoid structures does not require Id2-dependent conventional LTis but depends on a program initiated by mature CD3+CD4+ T cells.

AMD3465, a novel CXCR4 receptor antagonist, abrogates schistosomal antigen-elicited (type-2) pulmonary granuloma formation

CXCR4 is a major receptor for CXCL12 and is known to participate in multiple physiological systems. The present study tested a second generation CXCR4 antagonist, AMD3465, for effects on highly defined models of Th1- and Th2-cell-mediated hypersensitivity-type pulmonary granuloma formation. Type-1 and type-2 granulomas were induced, respectively, by intravenous challenge of sensitized CBA/J mice with Mycobacteria bovis purified protein derivative- or Schistosoma mansoni egg antigen-coated beads. Before challenge, mice were implanted with osmotic pumps releasing AMD3465 at 5 microg/hour (6 mg/kg/day). Compared to vehicle, AMD3465 had minimal effect on type-1 inflammation or cytokine responses in draining lymph nodes, but the type-2 inflammation was significantly abrogated with reductions in lesion size and eosinophil content as well as abrogated interleukin (IL)-5, IL-10, and IL-13 cytokine production in draining lymph nodes. The biased effect of AMD3465 correlated with greater CXCR4 ligand expression in the type-2 model. Treatment during a primary response impaired lymph node IL-2 production after both Mycobacteria bovis purified protein derivative and Schistosoma mansoni egg antigen challenge indicating an unbiased effect during immune induction. In summary, CXCR4 blockade inhibited eosinophil recruitment during type-2 granuloma formation and interfered with primary and secondary T-cell activation events in lymphoid tissue, suggesting potential therapeutic application for chronic hypersensitivity diseases.

Developmental stage-specific shift in responsiveness to chemokines during human B-cell development

OBJECTIVES

To better understand the role of chemokines during human B-cell development in bone marrow.

METHODS

Differentiation stage-specific B cells (pro-B, pre-B, immature, and mature) were analyzed for chemokine receptor expression and for migration to corresponding ligands. We also hypothesized that inflammatory conditions may cause the upregulation of certain chemokine receptors on early B cells, rendering them sensitive to extramedullary chemotactic cues. To test this hypothesis, we used human pre-B 697 cells to investigate whether various inflammatory agents could modify chemokine receptor expression and function.

RESULTS

Chemotaxis to CXCL12 was observed for all B cell subsets. However, chemotactic responses to CCL19, CCL21, CXCL13, and CCL20 were limited to late-stage, IgM+ bone marrow B cells (immature B and mature B). Chemotactic responses to corresponding ligands correlated with the pattern of chemokine receptor expression. The expression of CCR7, however, was low on early (pro-B and pre-B) B cells and did not induce chemotaxis. Interestingly, both CCL19 and CCL21 could trigger ERK1/2 phosphorylation in early B cells. Exposure of pre-B 697 cells to TNF-alpha upregulated CCR7 and CXCR5 expression, whereas it had no effect on CCR6 surface expression. Correspondingly, TNF-alpha-stimulated pre-B cells chemotaxed towards CCL19 and CXCL13, in contrast to non-TNF-alpha-stimulated controls.

CONCLUSION

We postulate that CXCR5, CCR7, and CCR6 participate in bone marrow trafficking and/or bone marrow egress of late-stage B cells under steady-state conditions, whereas inflammation-induced expression of CCR7 and CXCR5 may facilitate early B-cell emigration out of the bone marrow and their positioning in secondary lymphoid organs.

Expression of chemokines and gelatinase B in sympathetic ophthalmia

PURPOSE

To examine the expression of gelatinase B (matrix metalloproteinase-9) and the chemokines monocyte chemotactic protein-1 (CCL2/MCP-1) and stromal cell-derived factor-1 (CXCL12/SDF-1) in sympathetic ophthalmia (SO).

METHODS

Five enucleated exciting eyes with a clinical diagnosis and typical histopathological findings of SO were studied by immunohistochemical techniques using a panel of monoclonal antibodies directed against gelatinase B, MCP-1, and SDF-1. In addition, a panel of monoclonal and polyclonal antibodies was used to characterize the composition of the inflammatory infiltrate.

RESULTS

In all cases, the extensive uveal inflammatory infiltrate was organized as a diffuse infiltrate and as large granulomas consisting of epithelioid cells and multinucleated giant cells. CD20(+) B lymphocytes predominated in the diffuse infiltrate and CD3(+) T lymphocytes were few. The monocyte/macrophage marker CD68 was expressed in scattered inflammatory mononuclear cells and within granulomas and Dalen-Fuchs nodules. Most of the inflammatory cells were HLA-DR(+). Immunoreactivity for gelatinase B, MCP-1, and SDF-1 was observed in cells within granulomas and in scattered epithelioid cells. Immunoreactivity for MCP-1 was noted in retinal pigment epithelial cells. Endothelial cells of choriocapillaries showed weak immunoreactivity for SDF-1.

CONCLUSIONS

Gelatinase B, MCP-1, and SDF-1 might have a pathogenic role in the recruitment of leucocytes into the eye in SO.

Epstein-Barr virus infection negatively impacts the CXCR4-dependent migration of tonsillar B cells

The primary Epstein-Barr virus (EBV) infection occurs in the oropharynx, where the virus infects B cells and subsequently establishes latency in the memory B-cell compartment. EBV has previously been shown to induce changes in the cell surface expression of several chemokine receptors in cell lines and the transfection of EBNA2 or LMP1 into a B-cell-lymphoma-derived cell line decreased the expression of CXCR4. We show that in vitro EBV infection reduces the expression of CXCR4 on primary tonsil B cells already 43 hr after infection. Furthermore, EBV infection affects the chemotactic response to stromal cell-derived factor (SDF-1)alpha/CXCL12, the ligand for CXCR4, with a reduction of SDF-1alpha-induced migration. To clarify whether this reduced migration is EBV-specific or a consequence of cell activation, tonsillar B cells were either infected with EBV, activated with anti-CD40 and interleukin-4 (IL-4) or kept in medium. Activation by anti-CD40 and IL-4 decreased the CXCR4 expression but the CD40 + IL-4-stimulated cells showed no reduction of chemotactic efficacy. Our finding suggests that changing the SDF-1alpha response of the EBV-infected B cells may serve the viral strategy by directing the infected cells into the extrafollicular areas, rather than retaining them in the lymphoepithelium.

Hematopoietic stem cell trafficking in liver injury

Bone marrow (BM) hematopoietic stem cells (HSCs) have been shown to facilitate regeneration in multiple nonhematopoietic tissues by either generating epithelial cells or altering the inflammatory response. Depending on injury type, the predominant mechanism of epithelial lineage regeneration occurs by spontaneous cell fusion or transdifferentiation. Irrespective of the mechanism, mobilization from the BM is a prerequisite. Mechanisms by which HSCs mobilize into damaged organs are currently under scrutiny. Murine and human studies have shown that the chemokine SDF-1 and its receptor CXCR4 participate in the mobilization of HSCs from BM and in the migration of HSCs to injured liver. SDF-1 is a potent HSC chemoattractant and is produced by the liver. Production is increased during liver injury leading to increased HSC migration to the liver, a finding diminished by neutralizing anti-CXCR4 antibodies. Additional factors have been implicated in the control of hepatic migration of HSCs such as IL-8, hepatocyte growth factor, and MMP-9. Matriceal remodeling is an essential component in HSC engraftment, and MMP-9 expression is increased in liver injury. This review focuses on the complex interaction of chemokines, adhesion molecules, and extracellular matrix factors required for successful migration and engraftment of HSCs into the liver.

Chemotactic responses of IL-4-, IL-10-, and IFN-gamma-producing CD4+ T cells depend on tissue origin and microbial stimulus

Th1- and Th2-polarized immune responses are crucial in the defense against pathogens but can also promote autoimmunity and allergy. The chemokine receptors CXCR3 and CCR4 have been implicated in differential trafficking of IFN-gamma- and IL-4-producing T cells, respectively, but also in tissue and inflammation-specific homing independent of cytokine responses. Here, we tested whether CD4+ T cells isolated from murine tissues under homeostatic or inflammatory conditions exhibit restricted patterns of chemotactic responses that correlate with their production of IFN-gamma, IL-4, or IL-10. In uninfected mice, IL-4-producing T cells preferentially migrated to the CCR4 ligand, CCL17, whereas IFN-gamma-expressing T cells as well as populations of IL-4+ or IL-10+ T cells migrated to the CXCR3 ligand, CXCL9. All cytokine-producing T cell subsets strongly migrated to the CXCR4 ligand, CXCL12. We assessed chemotaxis of T cells isolated from mice infected with influenza A virus or the nematode Nippostrongylus brasiliensis, which induce a strong Th1 or Th2 response in the lung, respectively. Unexpectedly, the chemotactic responses of IL-4+ T cells and T cells expressing the immunosuppressive cytokine IL-10 were influenced not only by the strongly Th1- or Th2-polarized environments but also by their anatomical localization, i.e., lung or spleen. In contrast, IFN-gamma+ T cells exhibited robust chemotaxis toward CXCL9 and had the most consistent migration pattern in both infection models. The results support a model in which the trafficking responses of many effector and regulatory T cells are regulated as a function of the infectious and tissue environments.

Lsc regulates marginal-zone B cell migration and adhesion and is required for the IgM T-dependent antibody response

The humoral immune response to protein antigens is composed of a rapid low-affinity IgM antibody response followed by an IgG response exhibiting higher affinity. Here, we demonstrate that Lsc, a protein that regulates G protein-coupled-receptor signaling and RhoA activation, is required by B lymphocytes for the antigen-specific IgM antibody response to a protein antigen. We further show that in lsc(-/-) mice, MZB cells are selectively affected such that naive and in vivo-activated MZB cells migrate toward sphingosine-1-phosphate at increased proportions but release inefficiently from integrin ligands. Consequently, lsc(-/-) MZB cells do not traffick appropriately in an immune response and do not contribute to the TD antibody response. These data demonstrate that Lsc regulates the migration and adhesion of MZB cells, and this regulation appears to be required for these cells to contribute to the antibody response to TD antigens.

Mucosal B cells: phenotypic characteristics, transcriptional regulation, and homing properties

Mucosal antibody defense depends on a complex cooperation between local B cells and secretory epithelia. Mucosa-associated lymphoid tissue gives rise to B cells with striking J-chain expression that are seeded to secretory effector sites. Such preferential homing constitutes the biological basis for local production of polymeric immunoglobulin A (pIgA) and pentameric IgM with high affinity to the epithelial pIg receptor that readily can export these antibodies to the mucosal surface. This ultimate functional goal of mucosal B-cell differentiation appears to explain why the J chain is also expressed by IgG- and IgD-producing plasma cells (PCs) occurring at secretory tissue sites; these immunocytes may be considered as 'spin-offs' from early effector clones that through class switch are on their way to pIgA production. Abundant evidence supports the notion that intestinal PCs are largely derived from B cells initially activated in gut-associated lymphoid tissue (GALT). Nevertheless, insufficient knowledge exists concerning the relative importance of M cells, major histocompatibility complex class II-expressing epithelial cells, and professional antigen-presenting cells for the uptake, processing, and presentation of luminal antigens in GALT to accomplish the extensive and sustained priming and expansion of mucosal B cells. Likewise, it is unclear how the germinal center reaction in GALT so strikingly can promote class switch to IgA and expression of J chain. Although B-cell migration from GALT to the intestinal lamina propria is guided by rather well-defined adhesion molecules and chemokines/chemokine receptors, the cues directing preferential homing to different segments of the gut require better definition. This is even more so for the molecules involved in homing of mucosal B cells to secretory effector sites beyond the gut, and in this respect, the role of Waldever's ring (including the palatine tonsils and adenoids) as a regional inductive tissue needs further characterization. Data suggest a remarkable compartmentalization of the mucosal immune system that must be taken into account in the development of effective local vaccines to protect specifically the airways, eyes, oral cavity, small and large intestines, and urogenital tract.

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.

RGS16 is a negative regulator of SDF-1-CXCR4 signaling in megakaryocytes

Regulators of G-protein signaling (RGS) constitute a family of proteins involved in the negative regulation of signaling through heterotrimeric G protein-coupled receptors (GPCRs). Several RGS proteins have been implicated in the down-regulation of chemokine signaling in hematopoietic cells. The chemokine stromal-cell-derived factor 1 (SDF-1) activates migration of hematopoietic progenitors cells but fails to activate mature megakaryocytes despite high levels of CXC chemokine receptor 4 (CXCR4) receptor expression in these cells. This prompted us to analyze RGS expression and function during megakaryocyte differentiation. We found that RGS16 and RGS18 mRNA expression was up-regulated during this process. Overexpressing RGS16 mRNA in the megakaryocytic MO7e cell line inhibited SDF-1-induced migration, mitogen-activated protein kinase (MAPK) and protein kinase B (AKT) activation, whereas RGS18 overexpression had no effect on CXCR4 signaling. Knocking down RGS16 mRNA via lentiviral-mediated RNA interference increased CXCR4 signaling in MO7e cells and in primary megakaryocytes. Thus, our data reveal that RGS16 is a negative regulator of CXCR4 signaling in megakaryocytes. We postulate that RGS16 regulation is a mechanism that controls megakaryocyte maturation by regulating signals from the microenvironment.

Respiratory Vaccination of Mice Against Influenza Virus: Dissection of T- and B-Cell Priming Functions

We find that a single respiratory administration of replicationally inactivated influenza A viral particles most often elicits a waning serum antibody response, as the long-sustained bone marrow antiviral plasma cell populations characteristically induced by viral infection are lacking, though antiviral plasma cells at other sites may occasionally persist for a long time. To determine whether this alteration in the pattern of the B-cell response is a reflection of the nature of T-helper (Th) priming, we simultaneously primed B cells with inactivated influenza A/PR8(H1N1) and Th cells with infectious A/x31(H3N2). We show that Th cells cross-react extensively between these two viruses, although the antibody response to viral envelope glycoproteins is completely non-cross-reactive. Th cells primed by infectious A/x31 have little impact on the antibody response specifically elicted from naïve B cells by inactivated A/PR8 viruses, suggesting that the characteristic vigour of the antibody response to influenza viral infection depends on the direct interaction of antiviral B cells with virally infected dendritic cells. Memory B cells primed by inactivated influenza viral particles however, respond rapidly to secondary challenge with live or inactivated viruses, promptly populating bone marrow with antiviral plasma cells. Moreover, Th cells primed by previous live A/x31 viral challenge alter the pattern of the response of naïve B cells to live A/PR8 challenge by accelerating the appearance of anti-H1/N1 plasma cells in bone marrow, eliminating the early spike of anti-H1/N1 plasma cells in the mediastinal node, and generally diminishing the magnitude of the lymph node response. Inactivated A/PR8 and infectious A/x31 are both effective vaccines against A/PR8 infection, as mice preimmunized with either vaccine exhibit much more rapid viral clearance from the lung after infectious A/PR8 challenge. In fact, even when given during a course of anti-CD8 treatment to preempt cross-reactive cytotoxic T cells, live A/x31 is a more effective vaccine against A/PR8 infection than is inactivated A/PR8 itself.

Adaptive immune responses are dispensable for isolated lymphoid follicle formation: antigen-naive, lymphotoxin-sufficient B lymphocytes drive the formation of mature isolated lymphoid follicles

Isolated lymphoid follicles (ILFs) are recently appreciated members of the mucosal immune system. The architecture, composition, and inducible nature of these structures indicates that these structures are tertiary lymphoid structures. The process leading to the formation of tertiary lymphoid structures, lymphoid neogenesis, has been observed in a number of inflammatory and autoimmune conditions. Given this association, there is considerable interest in identifying the factors promoting lymphoid neogenesis, and understanding the steps in this process. Using murine ILF formation as a model, we have examined the roles of different cellular sources of lymphotoxin (LT) and the adaptive immune response in lymphoid neogenesis. In this study, we report that, although other cellular sources of LT may supplant B lymphocytes in the formation of immature ILFs (loosely organized clusters of B lymphocytes), LT-sufficient B lymphocytes are required for the progression of immature ILFs to mature ILFs (organized lymphoid aggregates with a follicle-associated epithelium). ILF formation occurs in the absence of T lymphocytes and Ag-specific B lymphocyte responses, and ILF B lymphocytes express elevated levels of LT in the absence of antigenic stimulation. Consistent with a role for chemokines inducing LT expression in Ag-naive B lymphocytes, and a chemokine-driven positive-feedback loop driving mature ILF formation, mature ILFs express elevated levels of B lymphocyte chemoattractant in the absence of Ag-specific B lymphocyte stimulation. These observations indicate that ILFs contain Ag-naive lymphocytes, and suggest that events occurring within ILFs shape subsequent immune responses mediated by these lymphocytes.

Interpreting two-photon imaging data of lymphocyte motility

Recently, using two-photon imaging it has been found that the movement of B and T cells in lymph nodes can be described by a random walk with persistence of orientation in the range of 2 minutes. We interpret this new class of lymphocyte motility data within a theoretical model. The model considers cell movement to be composed of the movement of subunits of the cell membrane. In this way movement and deformation of the cell are correlated to each other. We find that, indeed, the lymphocyte movement in lymph nodes can best be described as a random walk with persistence of orientation. The assumption of motility induced cell elongation is consistent with the data. Within the framework of our model the two-photon data suggest that T and B cells are in a single velocity state with large stochastic width. The alternative of three different velocity states with frequent changes of their state and small stochastic width is less likely. Two velocity states can be excluded.

A rich chemokine environment strongly enhances leukocyte migration and activities

The migration of leukocytes in immune surveillance and inflammation is largely determined by their response to chemokines. While the chemokine specificities and expression patterns of chemokine receptors are well defined, it is still a matter of debate how leukocytes integrate the messages provided by different chemokines that are concomitantly produced in physiologic or pathologic situations in vivo. We present evidence for a novel regulatory mechanism of leukocyte trafficking. Our data are consistent with a mode of action where CC-chemokine receptor 7 (CCR7) agonists and unrelated, nonagonist chemokines first form a heteromeric complex, in the presence of which the triggering of CCR7 can occur at a much lower agonist concentration. The increase is synergistic and can be evoked by many but not all chemokines. Chemokine-induced synergism might provide an amplification system in “chemokine-rich” tissues, rendering leukocytes more competent to respond to migratory cues.

B-lymphocytes, innate immunity, and autoimmunity

Having evolved to generate a huge Ag-specific repertoire and to mount T cell-dependent responses and long-term memory, the B lymphocyte is a central player in the adaptive branch of immune defense. However, accumulating evidence indicates that B-1 cells of the peritoneal cavity and marginal zone (MZ) B cells of the spleen also can play innate-like immune functions. Their anatomical locations allow frequent Ag encounter. Secreting essentially germline-encoded, polyreactive Abs, and responding rapidly and vigorously to stimulation, these two B cell subsets have evolved to impart potentially protective responses. With their additional capacities to secrete factors that can directly mediate microbial destruction and to express Toll-like receptors (TLR), B cells provide an important link between the innate and adaptive branches of the immune system. Currently, the relevance of these innate-like B cells to the pathogenesis of autoimmune disease is the focus of investigation. In experimental models of autoimmunity, the sequestration of autoreactive B cells in the MZ has been proposed to be essential for the maintenance of self-tolerance. The low activation threshold of MZ B cells makes them particularly reactive to high loads and/or altered self-Ags, potentially exacerbating autoimmune disease. Their expansion in autoimmune models and their association with autoantibody secretion indicate that they may participate in tissue damage. The demonstration that B cell depletion therapies may represent a highly beneficial therapeutic goal in autoimmune disorders suggests that specific elimination of B-1 and MZ B cells may represent a more efficient immunointervention strategy in systemic autoimmunity.

Early appearance of germinal center-derived memory B cells and plasma cells in blood after primary immunization

Immunization with a T cell–dependent antigen elicits production of specific memory B cells and antibody-secreting cells (ASCs). The kinetic and developmental relationships between these populations and the phenotypic forms they and their precursors may take remain unclear. Therefore, we examined the early stages of a primary immune response, focusing on the appearance of antigen-specific B cells in blood. Within 1 wk, antigen-specific B cells appear in the blood with either a memory phenotype or as immunoglobulin (Ig)G1 ASCs expressing blimp-1. The memory cells have mutated V_H genes; respond to the chemokine CXCL13 but not CXCL12, suggesting recirculation to secondary lymphoid organs; uniformly express B220; show limited differentiation potential unless stimulated by antigen; and develop independently of blimp-1 expression. The antigen-specific IgG1 ASCs in blood show affinity maturation paralleling that of bone marrow ASCs, raising the possibility that this compartment is established directly by blood-borne ASCs. We find no evidence for a blimp-1–expressing preplasma memory compartment, suggesting germinal center output is restricted to ASCs and B220⁺ memory B cells, and this is sufficient to account for the process of affinity maturation.

Regulation of CXCR3 and CXCR4 expression during terminal differentiation of memory B cells into plasma cells

C-X-C motif chemokine receptor 3 (CXCR3) and CXCR4 expressed on immunoglobulin G (IgG)-plasma-cell precursors formed in memory immune responses are crucial modulators of the homing of these cells. Here, we studied the regulation of the expression of these chemokine receptors during the differentiation of human memory B cells into plasma cells. We show that CXCR3 is absent on CD27- naive B cells but is expressed on a fraction of memory B cells, preferentially on those coexpressing IgG1. On differentiation into plasma-cell precursors, CXCR3+ memory B cells maintain the expression of this chemokine receptor. CXCR3- memory B cells up-regulate CXCR3 and migrate toward concentration gradients of its ligands only when costimulated with interferon gamma (IFN-gamma), but not interleukin 4 (IL-4), IL-1beta, IL-6, IFN-alpha, IFN-beta, or tumor necrosis factor alpha (TNF-alpha). In contrast, the differentiation of CXCR4- B cells into plasma cells is generally accompanied by the induction of CXCR4 expression. These results show that lack of CXCR4 expression on plasma-cell precursors is not a limiting factor for plasma-cell homing and that the expression of CXCR3 on memory B cells and plasma-cell precursors is induced by IFN-gamma, provided in human T helper type 1 (Th1)-biased immune responses. Once induced in memory B cells, CXCR3 expression remains part of the individual cellular memory.

CXCR4 mutations in WHIM syndrome: a misguided immune system?

Chemokines and their receptors are key molecules in the development and function of immune cell populations and the organization of lymphoid organs. Despite their central role in immunologic function, genetic studies exploring the intersection of chemokines or their receptors and human health have revealed few associations of unambiguous significance. The best-characterized examples have revealed striking selective advantage conferred by loss of receptors used as portals of entry by pathogens. Recently, mutations in the CXCR4 chemokine receptor gene were identified in a dominantly inherited immunodeficiency disease, WHIM syndrome. Genetic and biochemical evidences suggest that the loss of the receptor cytoplasmic tail domain results in aberrant signaling. Analyses of mutant cell responses to the receptor ligand CXCL12 have revealed enhanced chemotaxis, confirming the gain-of-function effect of the truncation mutations. The clinical features and potential mechanism of immunodeficiency in WHIM syndrome patients are discussed in this review.

Dysregulation of chemokine receptor expression and function by B cells of patients with primary Sjögren's syndrome

OBJECTIVE

To assess whether abnormal chemokine receptor expression and/or abnormal responsiveness to the cognate ligands might underlie some of the disturbances in B cell homeostasis characteristic of primary Sjögren's syndrome (SS).

METHODS

Chemokine receptor expression by CD27- naive and CD27+ memory B cells from patients with primary SS and healthy control subjects was analyzed using flow cytometry, single-cell reverse transcriptase-polymerase chain reaction (RT-PCR), and migration assays.

RESULTS

In contrast to healthy subjects, significantly higher expression of both surface CXCR4 and CXCR4 messenger RNA (mRNA) was seen in peripheral blood B cells from patients with primary SS. These differences were most prominent in CD27- naive B cells (P < or = 0.0006). In addition, significantly higher frequencies of CD27- naive B cells from patients with primary SS expressed mRNA for the inhibitory regulator of G protein signaling 13 (P = 0.001). Expression of CXCR5 by peripheral CD27+ memory B cells was moderately diminished in patients with primary SS compared with healthy controls (P = 0.038). No significant differences were noted in the expression of CXCR3, CCR6, CCR7, and CCR9 between B cells from healthy controls and those from patients with primary SS. Transmigration assays of blood B cells from patients with primary SS and healthy controls showed comparable responses of CD27- naive B cells but significantly diminished responses of activated primary SS CD27+ memory B cells to the ligands of CXCR4 and CXCR5, CXCL12 (P = 0.032), and CXCL13 (B lymphocyte chemoattractant; B cell-attracting chemokine 1; P = 0.018), respectively, when compared with those from healthy controls. Finally, compared with controls, peripheral reduction but glandular accumulation of CXCR4+,CXCR5+,CD27+ memory B cells was identified in patients with primary SS.

CONCLUSION

In primary SS, overexpression of CXCR4 by circulating blood B cells does not translate into enhanced migratory response to the cognate ligand, CXCL12. This migratory response may be modulated by intracellular regulators. Retention of CXCR4+,CXCR5+, CD27+ memory B cells in the inflamed glands seems to contribute to diminished peripheral CD27+ memory B cells in primary SS.

The significance of cancer cell expression of the chemokine receptor CXCR4

Malignant cells from at least 23 different types of cancer express the chemokine receptor CXCR4 and respond to its ligand CXCL12. This receptor ligand pair appears to be involved in directed migration of cancer cells to sites of metastasis, increased survival of cancer cells in sub optimal conditions and establishment of a tumour promoting cytokine/chemokine network. Preliminary data from animal models suggest that CXCR4 may be an important therapeutic target in a range of cancers. However CXCR4 plays major roles in embryogenesis, homeostasis and inflammation. This raises questions concerning the specificity of CXCR4 antagonists in the treatment of cancer.

Stromal cell-derived factor-1 (SDF-1) signalling regulates human placental trophoblast cell survival

Stromal cell-derived factor-1 (SDF-1 or CXCL12) is the physiologic ligand for the chemokine receptor CXCR4. CXCR4-mediated signalling regulates cell migration and apoptosis in certain haematopoietic and neuronal cells. Using gene profiling, we determined that CXCR4 is the only chemokine receptor for which mRNA expression is regulated during trophoblast differentiation in vitro. Based on the known effects of CXCR4 ligation, we hypothesized that CXCR4 activation may regulate placental trophoblast cell survival (i.e. protection from apoptosis), an important mechanism for the establishment and maintenance of the uteroplacental barrier. Human cytotrophoblasts (CTBs) were cultured in defined media and treated with graded doses of SDF-1 (10-100 ng/ml) or with an anti-CXCR4 neutralizing antibody. Exposure to anti-CXCR4 antibody reduced CTB cell numbers by 25-40%. Treatment with SDF-1 decreased the proportions of apoptotic terminal deoxynucleotidyl transferase-mediated dUTP-FITC nick-end labelling(+) cells (apoptotic index [AI] of 2.79+/-0.61% [control] versus 1.88+/-0.56% [SDF-1]; P<0.05) and caspase-activated cells (AI of 7.95+/-2.49% [control] versus 3.81+/-1.49% [SDF-1]; P<0.05). We determined that SDF-1 also activated the triple MAP Kinase isoforms ERK1/2 and p38 in trophoblasts. Immunocytochemistry confirmed SDF-1-induced nuclear translocation of phosphorylated ERK1/2. Blocking of ERK1/2 signalling with the specific inhibitor PD98059 reversed SDF-1-mediated inhibition of apoptosis (AI of 1.65+/-0.34 [SDF-1] versus 3.50+/-0.5 [SDF-1 + PD98059]; P<0.05), suggesting that SDF-1 acts through this pathway as a trophoblast survival factor. These results indicate that SDF-1/CXCR4 signalling stimulates anti-apoptotic pathways in cultured trophoblasts. This chemotactic ligand/receptor system may promote trophoblast survival during pregnancy. Alterations in SDF-1 and/or CXCR4 expression or function may be associated with specific pregnancy disorders.

Follicular Dendritic Cell Regulation of CXCR4-Mediated Germinal Center CD4 T Cell Migration

Follicular dendritic cells (FDCs) up-regulate the chemokine receptor CXCR4 on CD4 T cells, and a major subpopulation of germinal center (GC) T cells (CD4(+)CD57(+)), which are adjacent to FDCs in vivo, expresses high levels of CXCR4. We therefore reasoned that GC T cells would actively migrate to stromal cell-derived factor-1 (CXCL12), the CXCR4 ligand, and tested this using Transwell migration assays with GC T cells and other CD4 T cells (CD57(-)) that expressed much lower levels of CXCR4. Unexpectedly, GC T cells were virtually nonresponsive to CXCL12, whereas CD57(-)CD4 T cells migrated efficiently despite reduced CXCR4 expression. In contrast, GC T cells efficiently migrated to B cell chemoattractant-1/CXCL13 and FDC supernatant, which contained CXCL13 produced by FDCs. Importantly, GC T cell nonresponsiveness to CXCL12 correlated with high ex vivo expression of regulator of G protein signaling (RGS), RGS13 and RGS16, mRNA and expression of protein in vivo. Furthermore, FDCs up-regulated both RGS13 and RGS16 mRNA expression in non-GC T cells, resulting in their impaired migration to CXCL12. Finally, GC T cells down-regulated RGS13 and RGS16 expression in the absence of FDCs and regained migratory competence to CXCL12. Although GC T cells express high levels of CXCR4, signaling through this receptor appears to be specifically inhibited by FDC-mediated expression of RGS13 and RGS16. Thus, FDCs appear to directly affect GC T cell migration within lymphoid follicles.

In multiple myeloma clonotypic CD38- /CD19+ / CD27+ memory B cells recirculate through bone marrow, peripheral blood and lymph nodes

It is believed that myeloma cells are derived from a germinal center (GC) or post GC B cell. The GC B cell can differentiate into both a memory B cell and a plasma cell (PC). In this study, we investigated the recirculating potential of memory B cells clonally related to the myeloma PC (termed clonotypic). The V(H)DJ(H) immunoglobulin gene rearrangement of the myeloma clone was identified for 10 myeloma patients and allele-specific oligonucleotides (ASO) IgH RT-PCR assays were designed for each patient. Memory B cells (CD38- /CD19+ /CD27+) and their subsets defined by the monoclonal antibodies CD62L, CCR6, CXCR4, CXCR5, CCR7 were flow-sorted as single cells and analyzed by ASO RT-PCR analysis. In addition, aspirated peripheral lymph nodes (PLN) of 7 myeloma patients in complete or partial remission were analyzed for the presence of clonotypic cells. Circulating clonotypic memory B cells were identified in PBMNC of 7/10 patients and both CD62L positive and negative clonotypic memory B cells were identified. Furthermore, comparable frequencies of clonotypic cells were found in the CCR6 +/- and CXCR4 +/- memory B cell subsets, whereas all clonotypic memory and later stage B cells were CXCR5 positive. In accordance with their immunophenotype, clonotypic memory B-cells were identified in peripheral blood, bone marrow and PLNs. Clonotypic memory B-cells were present in the majority of myeloma patients and seem to have the same diverse recirculating/homing capacity as normal memory B cells.

High-level expression of functional chemokine receptor CXCR4 on human neural precursor cells

Neural precursor cells (NPCs) are self-renewing, multipotent progenitors that give rise to neurons, astrocytes and oligodendrocytes in the central nervous system (CNS). Fetal NPCs have attracted attention for their potential use in studying normal CNS development. Several studies of rodent neural progenitors have suggested that chemokines and their receptors are involved in directing NPC migration during CNS development. In this study, we established a consistent system to culture human NPCs and examined the expression of chemokine receptors on these cells. NPCs were found to express the markers nestin and CD133 and to differentiate into neurons, astrocytes and oligodendrocytes at the clonal level. Flow cytometry and RNase protection assay (RPA) indicated that NPCs express high levels of CXCR4 and low levels of several other chemokine receptors. When examined using a chemotaxis assay, NPCs were able to respond to CXCL12/SDF-1alpha, a ligand of CXCR4. Treatment with anti-CXCR4 antibody or HIV-1 gp120 abolished the migratory response of NPCs towards CXCL12/SDF-1alpha. These findings suggest that CXCR4 may play a significant role in directing NPC migration during CNS development.

Germinal center dark and light zone organization is mediated by CXCR4 and CXCR5

Germinal center (GC) dark and light zones segregate cells undergoing somatic hypermutation and antigen-driven selection, respectively, yet the factors guiding this organization are unknown. We report here that GC organization was absent from mice deficient in the chemokine receptor CXCR4. Centroblasts had high expression of CXCR4 and GC B cells migrated toward the CXCR4 ligand SDF-1 (CXCL12), which was more abundant in the dark zone than in the light zone. CXCR4-deficient cells were excluded from the dark zone in the context of a wild-type GC. These findings establish that GC organization depends on sorting of centroblasts by CXCR4 into the dark zone. In contrast, CXCR5 helped direct cells to the light zone and deficiency in CXCL13 was associated with aberrant light zone localization.

Homeostatic chemokines drive migration of malignant B cells in patients with non-Hodgkin lymphomas

This study investigated the role of several chemokines and their receptors on malignant B lymphocytes recovered from 13 patients with chronic lymphocytic leukemia (CLL), 9 with hairy cell leukemia (HCL), 5 with mantle cell lymphoma (MCL), 5 with marginal zone B-cell lymphoma (MZL), 6 with small lymphocytic lymphoma (SLL), and 5 with follicular cell lymphoma (FCL). Flow cytometry analysis demonstrated that CXCR4 and CXCR5 were expressed on all malignant and normal B cells. Considering CC receptors, CCR1 was expressed in 70% of patients with CLL and 40% of those with HCL but was lacking in patients with MCL, MZL, SLL, and normal B cells. CCR2 showed a heterogeneous pattern of expression. CCR3 was found in almost all patients with CLL and in the majority of those with HCL, whereas it was usually lacking in patients with MZL and SLL and in healthy subjects. CCR5 was expressed in patients with HCL and MCL. Migration assays showed that different chemokines, mainly CXCL12 and CXCL13, are able to trigger migration of malignant B lymphocytes. Some of these chemokines induce calcium mobilization. These data indicate that different patterns of chemokine receptor expression identify different malignant B-cell subsets and that these receptors are functional and might play a role in malignant B-cell circulation. (Blood. 2004;104:502-508)

Chemokine receptors that mediate B cell homing to secondary lymphoid tissues are highly expressed in B cell chronic lymphocytic leukemia and non-Hodgkin lymphomas with widespread nodular dissemination

B cell neoplasms present heterogeneous patterns of lymphoid organ involvement, which may be a result of the differential expression of chemokine receptors. We found that chemokine receptor (CCR)7, CXC chemokine receptor (CXCR)4, or CXCR5, the main chemokine receptors that mediate B cell entry into secondary lymphoid tissues and their homing to T cell and B cell zones therein, were highly expressed in B malignancies with widespread involvement of lymph nodes. Conversely, those pathologies with little or no nodular dissemination showed no expression to very low levels of CCR7 and CXCR5 and low to moderate levels of CXCR4. These findings provide evidence for the role of CCR7, CXCR4, and CXCR5 in determining the pattern of lymphoid organ involvement of B tumors. Functional studies were performed on B malignancies expressing different levels of CCR7, CXCR5, and CXCR4. Multiple myeloma (MM) cells did not express CCR7 nor CXCR5 and did not migrate in response to their ligands; a moderate expression of CXCR4 on MM cells was accompanied by a migratory response to its ligand, CXCL12. By contrast, cells from B cell chronic lymphocytic leukemia (B-CLL) expressed the highest levels of these chemokine receptors and efficiently migrated in response to all ligands of CCR7, CXCR4, and CXCR5. In addition, the migration index of B-CLL cells in response to both of the CCR7 ligands correlated with the presence of clinical lymphadenopathy, thus indicating that the high expression of functional chemokine receptors justifies the widespread character of B-CLL, representing a clinical target for the control of tumor cell dissemination.

CCL19/CCL21-triggered signal transduction and migration of dendritic cells requires prostaglandin E2

The control of dendritic cell (DC) migration is pivotal for the initiation of cellular immune responses. When activated with inflammatory stimuli, the chemokine receptor CCR7 is up-regulated on DCs. Activated DCs home to lymphoid organs, where the CCR7 ligands CCL19 and CCL21 are expressed. We previously found that human monocyte-derived DCs (MoDCs) exclusively migrated to CCL19 and CCL21 when matured in the presence of prostaglandin (PG) E2. Because PGE2 did not alter CCR7 cell surface expression, we examined whether PGE2 may exert its effect by coupling CCR7 to signal transduction modules. Indeed, stimulation with CCR7 ligands led to enhanced phosphatidylinositol-3-kinase–mediated phosphorylation of protein kinase B when MoDCs were matured in the presence of PGE2. Moreover, CCL19/CCL21-induced intracellular calcium mobilization in MoDCs occurred only when PGE2 was present during maturation. MoDC migration to CCL19 and CCL21 was dependent on phospholipase C and intracellular calcium flux but not on phosphatidylinositol-3 kinase. Hence, our data provide insight into CCL19/CCL21-triggered signal transduction pathways and identify a novel function for PGE2 in controlling the migration of mature MoDCs by facilitating CCR7 signal transduction.

Expression of the chemokine receptors CXCR4 and CCR7 and disease progression in B-cell chronic lymphocytic leukemia/ small lymphocytic lymphoma

OBJECTIVE

To assess the clinical relevance of chemokine receptor expression on the progression of B-cell chronic lymphocytic leukemia (B-CLL).

PATIENTS AND METHODS

Peripheral blood mononuclear cells from 45 patients with B-CLL were purified and compared with lymph node samples collected from 17 of these patients. Also compared were B cells obtained from peripheral blood samples from 5 healthy controls and B cells from reactive lymph nodes from 3 otherwise healthy persons. The patients were treated at the Mayo Clinic in Rochester, Minn, between January 15,1991, and February 7, 2003. Mononuclear cells were stained by a 2-color (fluorescein isothiocyanate/phycoerythrin) flow cytometric assay using antibodies to the chemokine receptors (CXCR1, CXCR2, CXCR3, CXCR4, CXCR5, CCR2, CCR4, CCR5, CCR6, and CCR7) and also to CD19.

RESULTS

Of the 45 patients in this study, 20 had Rai stage 0 disease, 12 had stage I disease, 3 had stage II disease, 2 had stage III disease, and 8 had stage IV disease. The mean fluorescent intensity (MFI) of the chemokine receptor expression on B-CLL cells was compared with normal controls and was not significantly different, except for an increase in the median expression of CXCR3 (P = .003) and CCR7 (P = .001) on B-CLL cells. We also found a significant increase in the expression of CXCR4 and CCR7 in B-CLL cells from patients with stage IV compared with stage 0 disease (P = .001 and P = .02, respectively). Furthermore, circulating B-CLL cells showed significantly higher expression of CXCR4 and CCR7 when compared with B lymphocytes in lymph nodes (P = .003 and P < .001, respectively).

CONCLUSION

The expression of CXCR4 and CCR7 on B-CLL cells correlates with Rai stage. Also, these chemokine receptors may be down-regulated once malignant B cells enter the lymph nodes. To our knowledge, this is the first published report that shows the strong association of Rai stage with CXCR4 and CCR7 expression levels in B-CLL cells.

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.

Complexity within the plasma cell compartment of mice deficient in both E- and P-selectin: implications for plasma cell differentiation

Antibody-secreting plasma cells represent the critical end-stage effector cells of the humoral immune response. Here, we show that several distinct plasma cell subsets are concurrently present in the lymph nodes, spleen, and bone marrow of mice deficient in both E- and P-selectin. One of these subsets was a B220-negative immunoglobulin g (IgG) plasma cell population expressing low to negative surface levels of syndecan-1. Examination of the chemotactic responsiveness of IgG plasma cell subsets revealed that migration toward stromal cell-derived factor 1/CXC ligand 12 (SDF-1/CXCL12) was primarily limited to the B220-lo subset regardless of tissue source. Although B220-negative plasma cells did not migrate efficiently in response to CXCL12 or to other chemokines for which receptor mRNA was expressed, these cells expressed substantial surface CXC chemokine receptor-4 (CXCR4), and CXCL12 stimulation rapidly induced extracellular signal regulated kinase 1 (ERK1)/ERK2 phosphorylation, demonstrating that CXCR4 retained signaling capacity. Therefore, B220-negative plasma cells exhibit a selective uncoupling of chemokine receptor expression and signaling from migration. Taken together, our findings document the presence of significant heterogeneity within the plasma cell compartment, which suggests a complex step-wise scheme of plasma cell differentiation in which the degree of differentiation and tissue location can influence the chemotactic responsiveness of IgG plasma cells.

WHIM syndrome: a genetic disorder of leukocyte trafficking

PURPOSE OF REVIEW

WHIM syndrome (the association of warts, hypogammaglobulinemia, recurrent bacterial infections, and 'myelokathexis') is a rare congenital form of neutropenia associated with an unusual immune disorder involving hypogammaglonulinemia and abnormal susceptibility to warts. In this review, we describe the clinical, laboratory and genetic features of WHIM syndrome.

RECENT FINDINGS

The identification of chemokine receptor CXCR4 as the causative gene of WHIM syndrome yields new interest in the study of this disease as a model for the comprehension of CXCR4 biology in humans and highlights the importance of the chemokine network for inducing effective immune responses and governing leukocyte trafficking.

SUMMARY

CXCR4 participates in several biological processes (bone marrow hematopoiesis, cardiogenesis, angiogenesis, neurogenesis) and is implicated in different clinical pathologic conditions (WHIM, HIV infection, tumor metastatization, autoimmunity). Pharmacologic agents that modulate CXCR4 expression/function are already available and promise a wide range of future clinical applications.

Plasma-cell homing

Recent studies indicate that chemoattractant cytokines (chemokines), together with tissue-specific adhesion molecules, coordinate the migration of antibody-secreting cells (ASCs) from their sites of antigen-driven differentiation in lymphoid tissues to target effector tissues. Developing ASCs downregulate the expression of receptors for lymphoid tissue chemokines and selectively upregulate the expression of chemokine receptors that might target the migration of IgA ASCs to mucosal surfaces, IgG ASCs to sites of tissue inflammation and both types of ASC to the bone marrow - an important site for serum antibody production. By directing plasma-cell homing, chemokines might help to determine the character and efficiency of mucosal, inflammatory and systemic antibody responses.

Tuning of Innate Immunity and Polarized Responses by Decoy Receptors

After the identification of the interleukin (IL)-1 type II receptor as the prototype, decoy receptors have been identified for a number of members of the IL-1/IL-18, TNF, IL-10 and IL-13 receptor families. Moreover, the silent receptor D6 is a promiscuous decoy and scavenger receptor of inflammatory chemokines. The IL-1 decoy receptor is regulated by pro- and anti-inflammatory signals and its levels may serve as a readout of the activation of anti-inflammatory pathways, for instance by glucocorticoid hormones. Decoy receptors represent a strategy to tune inflammatory and polarized adaptive responses.

Transforming growth factor-beta1 down-regulates expression of chemokine stromal cell-derived factor-1: functional consequences in cell migration and adhesion

Chemokine stromal cell-derived factor-1 (SDF-1) is expressed by bone marrow (BM) stromal cells and plays key roles in BM cell migration. Modulation of its expression could affect the migratory capacity of cells trafficking the BM, such as hematopoietic progenitor and leukemic cells. Transforming growth factor-beta1 (TGF-beta1) is present in the BM environment and constitutes a pivotal molecule controlling BM cell proliferation and differentiation. We used the BM stromal cell line MS-5 as a model to investigate whether SDF-1 expression constitutes a target for TGF-beta1 regulation and its functional consequences. We show here that TGF-beta1 down-regulates SDF-1 expression, both at the mRNA level, involving a decrease in transcriptional efficiency, and at the protein level, as detected in lysates and supernatants from MS-5 cells. Reduction of SDF-1 in supernatants from TGF-beta1-treated MS-5 cells correlated with decreased, SDF-1-dependent, chemotactic, and transendothelial migratory responses of the BM model cell lines NCI-H929 and Mo7e compared with their responses to supernatants from untreated MS-5 cells. In addition, supernatants from TGF-beta1-exposed MS-5 cells had substantially lower efficiency in promoting integrin alpha4beta1-mediated adhesion of NCI-H929 and Mo7e cells to soluble vascular cell adhesion molecule-1 (sVCAM-1) and CS-1/fibronectin than their untreated counterparts. Moreover, human cord blood CD34+ hematopoietic progenitor cells displayed SDF-1-dependent reduced responses in chemotaxis, transendothelial migration, and up-regulation of adhesion to sVCAM-1 when supernatants from TGF-beta1-treated MS-5 cells were used compared with supernatants from untreated cells. These data indicate that TGF-beta1-controlled reduction in SDF-1 expression influences BM cell migration and adhesion, which could affect the motility of cells trafficking the bone marrow.

Differential chemokine responses and homing patterns of murine TCR alpha beta NKT cell subsets

NKT cells play important roles in the regulation of diverse immune responses. Therefore, chemokine receptor expression and chemotactic responses of murine TCRalphabeta NKT cells were examined to define their homing potential. Most NKT cells stained for the chemokine receptor CXCR3, while >90% of Valpha14i-positive and approximately 50% of Valpha14i-negative NKT cells expressed CXCR6 via an enhanced green fluorescent protein reporter construct. CXCR4 expression was higher on Valpha14i-negative than Valpha14i-positive NKT cells. In spleen only, subsets of Valpha14i-positive and -negative NKT cells also expressed CXCR5. NKT cell subsets migrated in response to ligands for the inflammatory chemokine receptors CXCR3 (monokine induced by IFN-gamma/CXC ligand (CXCL)9) and CXCR6 (CXCL16), and regulatory chemokine receptors CCR7 (secondary lymphoid-tissue chemokine (SLC)/CC ligand (CCL)21), CXCR4 (stromal cell-derived factor-1/CXCL12), and CXCR5 (B cell-attracting chemokine-1/CXCL13); but not to ligands for other chemokine receptors. Two NKT cell subsets migrated in response to the lymphoid homing chemokine SLC/CCL21: CD4(-) Valpha14i-negative NKT cells that were L-selectin(high) and enriched for expression of Ly49G2 (consistent with the phenotype of most NKT cells found in peripheral lymph nodes); and immature Valpha14i-positive cells lacking NK1.1 and L-selectin. Mature NK1.1(+) Valpha14i-positive NKT cells did not migrate to SLC/CCL21. BCA-1/CXCL13, which mediates homing to B cell zones, elicited migration of Valpha14i-positive and -negative NKT cells in the spleen. These cells were primarily CD4(+) or CD4(-)CD8(-) and were enriched for Ly49C/I, but not Ly49G2. Low levels of chemotaxis to CXCL16 were only detected in Valpha14i-positive NKT cell subsets. Our results identify subsets of NKT cells with distinct homing and localization patterns, suggesting that these populations play specialized roles in immunological processes in vivo.

Activating and inhibitory Ly49 receptors modulate NK cell chemotaxis to CXC chemokine ligand (CXCL) 10 and CXCL12

NK cells can migrate into sites of inflammatory responses or malignancies in response to chemokines. Target killing by rodent NK cells is restricted by opposing signals from inhibitory and activating Ly49 receptors. The rat NK leukemic cell line RNK16 constitutively expresses functional receptors for the inflammatory chemokine CXC chemokine ligand (CXCL)10 (CXCR3) and the homeostatic chemokine CXCL12 (CXCR4). RNK-16 cells transfected with either the activating Ly49D receptor or the inhibitory Ly49A receptor were used to examine the effects of NK receptor ligation on CXCL10- and CXCL12-mediated chemotaxis. Ligation of Ly49A, either with Abs or its MHC class I ligand H2-D(d), led to a decrease in chemotactic responses to either CXCL10 or CXCL12. In contrast, Ly49D ligation with Abs or H2-D(d) led to an increase in migration toward CXCL10, but a decrease in chemotaxis toward CXCL12. Ly49-dependent effects on RNK-16 chemotaxis were not the result of surface modulation of CXCR3 or CXCR4 as demonstrated by flow cytometry. A mutation of the Src homology phosphatase-1 binding motif in Ly49A completely abrogated Ly49-dependent effects on both CXCL10 and CXCL12 chemotaxis, suggesting a role for Src homology phosphatase-1 in Ly49A/chemokine receptor cross-talk. Ly49D-transfected cells were pretreated with the Syk kinase inhibitor Piceatannol before ligation, which abrogated the previously observed changes in migration toward CXCL10 and CXCL12. Piceatannol also abrogated Ly49A-dependent inhibition of chemotaxis toward CXCL10, but not CXCL12. Collectively, these data suggest that Ly49 receptors can influence NK cell chemotaxis within sites of inflammation or tumor growth upon interaction with target cells.

CCR3 expression induced by IL-2 and IL-4 functioning as a death receptor for B cells

We report that CCR3 is not expressed on freshly isolated peripheral and germinal B cells, but is up-regulated after stimulation with IL-2 and IL-4 (approximately 98% CCR3(+)). Ligation of CCR3 by eotaxin/chemokine ligand (CCL) 11 induces apoptosis in IL-2- and IL-4-stimulated primary CD19(+) (approximately 40% apoptotic cells) B cell cultures as well as B cell lines, but has no effect on chemotaxis or cell adhesion. Freshly isolated B cells express low levels of CD95 and CD95 ligand (CD95L) (19 and 21%, respectively). Expression is up-regulated on culture in the presence of a combination of IL-2, IL-4, and eotaxin/CCL11 (88% CD95 and 84% CD95L). We therefore propose that ligation of such newly induced CCR3 on peripheral and germinal B cells by eotaxin/CCL11 leads to the enhanced levels of CD95 and CD95L expression. Ligation of CD95 by its CD95L expressed on neigboring B cells triggers relevant death signaling pathways, which include an increase in levels of Bcl-2 expression, its functional activity, and the release of cytochrome c from the mitochondria into the cytosol. These events initiate a cascade of enzymatic processes of the caspase family, culminating in programmed cell death. Interaction between CCR3 and eotaxin/CCL11 may, besides promoting allergic reactions, drive activated B cells to apoptosis, thereby reducing levels of Ig production, including IgE, and consequently limit the development of the humoral immune response. The apoptotic action of eotaxin/CCL11 suggests a therapeutic modality in the treatment of B cell lymphoma.

BCA-1, A B-cell chemoattractant signal, is constantly expressed in cutaneous lymphoproliferative B-cell disorders

We analysed the immunophenotypic and molecular expression of BCA-1 (B-cell-specific chemokine) and CXCR5 (BCA-1 receptor) in normal skin and different cutaneous lymphoproliferative disorders (cutaneous T-cell lymphoma (CTCL); cutaneous B-cell lymphoma (CBCL); cutaneous B-cell pseudolymphoma (PCBCL)), with the aim of investigating their possible involvement in the pathogenesis of cutaneous B-cell disorders. BCA-1 and CXCR5 were constantly expressed in CBCL and PCBCL, but not in normal skin and CTCL. BCA-1 and CXCR5 were constantly coexpressed by CD22+ B-cells, while CD35+ follicular dendritic cells coexpressed BCA-1 in PCBCL cells only. In low grade CBCL, as compared with high grade CBCL, the intensity of CXCR5 expression on neoplastic CD22+ cells was lower than that of BCA-1. The image analysis of reverse transcriptase-polymerase chain reaction (RT-PCR) products showed a significant quantitative difference between PCBCL/low grade CBCL and high grade CBCL. The above findings, although only observed in a small series of patients, are in keeping with findings in MALT gastric and gastric MALT lymphomas, adding further evidence of the close similarities between CBCL and MALT lymphomas.

Role of the chemokine stromal cell-derived factor 1 in autoantibody production and nephritis in murine lupus

In normal mice, stromal cell-derived factor 1 (SDF-1/CXCL12) promotes the migration, proliferation, and survival of peritoneal B1a (PerB1a) lymphocytes. Because these cells express a self-reactive repertoire and are expanded in New Zealand Black/New Zealand White (NZB/W) mice, we tested their response to SDF-1 in such mice. PerB1a lymphocytes from NZB/W mice were exceedingly sensitive to SDF-1. This greater sensitivity was due to the NZB genetic background, it was not observed for other B lymphocyte subpopulations, and it was modulated by IL-10. SDF-1 was produced constitutively in the peritoneal cavity and in the spleen. It was also produced by podocytes in the glomeruli of NZB/W mice with nephritis. The administration of antagonists of either SDF-1 or IL-10 early in life prevented the development of autoantibodies, nephritis, and death in NZB/W mice. Initiation of anti-SDF-1 mAb treatment later in life, in mice with established nephritis, inhibited autoantibody production, abolished proteinuria and Ig deposition, and reversed morphological changes in the kidneys. This treatment also counteracted B1a lymphocyte expansion and T lymphocyte activation. Therefore, PerB1a lymphocytes are abnormally sensitive to the combined action of SDF-1 and IL-10 in NZB/W mice, and SDF-1 is key in the development of autoimmunity in this murine model of lupus.

Expression of chemokine receptors, CXCR4 and CXCR5, and chemokines, BLC and SDF-1, in the eyes of patients with primary intraocular lymphoma

OBJECTIVE

Chemokines have a range of biologic activities, including regulation of leukocyte trafficking, modulation of hematopoietic cell proliferation, and adhesion to extracellular matrix molecules. Specifically, B-lymphocyte chemoattractant (BLC); BCA-1; CXCL13, SCYB13) and stromal cell-derived factor-1 (SDF-1, CXCL12, SCYB12) are chemotactic for human B cells, and their ligands CXCR4 and CXCR5 are differentially expressed on B cells, including malignant B cells. We investigated the expression of these chemokine/chemokine receptors in eyes with primary intraocular B-cell lymphoma (PIOL).

DESIGN

Observational case series (human tissue study).

METHODS

Three freshly enucleated eyes with PIOL and a normal autopsied eye were frozen and sectioned. The sections were evaluated using immunohistochemistry (avidin-biotin-complex immunoperoxidase technique) for CXCR4, CXCR5, BLC, and SDF-1 to detect the expression and location. Reverse transcriptase-polymerase chain reaction was used to detect chemokine transcripts of CXCR4, CXCR5, BLC, and SDF-1 in PIOL and retinal pigment epithelium (RPE) cells after microdissection-either by laser capture (Arcturus) or by manual dissection-from frozen sections.

MAIN OUTCOME MEASURES AND RESULTS

The three PIOL eyes showed similar pathology, with typical diffuse large B-lymphoma cells subjacent to the RPE. The eyes also demonstrated a similar chemokine profile. High expression levels of CXCR4 and CXCR5 were found limited to the lymphoma cells. In contrast, BLC protein was expressed in the RPE but not located in other ocular resident cells. SDF-1 was barely detected in a few RPE cells. CXCR4 and CXCR5 transcripts were detected abundantly in lymphoma cells, whereas BLC and SDF-1 transcripts were detected only in the RPE and not the malignant cells. No chemokine expression was detected on the RPE cells in the normal control eye.

CONCLUSIONS

Chemokines and chemokine receptors selective for B cells were identified in RPE and malignant B cells, respectively. BLC, and possibly SDF-1, attracts both normal and malignant B-cells while promoting migration of only small numbers of T cells and macrophages. We propose that B-cell chemokines may be involved in the pathogenesis of PIOL by selectively attracting lymphoma cells to the RPE from the choroidal circulation. Our data suggest that inhibition of B-cell chemoattractants could be a future strategy for the treatment of PIOL.