Chemokines induce eosinophil degranulation through CCR-3

BACKGROUND: Such CC chemokines as eotaxin and RANTES induce preferential eosinophil recruitment in allergic inflammation. They also elicit proinflammatory effector functions of eosinophils, such as enhanced adhesion and superoxide generation. Eosinophil degranulation by chemokines, however, has not been studied in detail. OBJECTIVE: The purpose of this study was to identify chemokines and their corresponding receptors that induce eosinophil degranulation by using a panel of chemokines and blocking antibodies to candidate receptors. METHODS: Highly purified eosinophils were preloaded with Fura-2 and stimulated with a panel of chemokine ligands for 14 known chemokine receptors: CCR1 to CCR8, CXCR1 to CXCR4, CX3CR1, and XCR1. Calcium influx was measured with fluorescence spectrometry. Eosinophils were also stimulated with the chemokines in the presence or absence of IL-5, and levels of eosinophil-derived neurotoxin were measured in the supernatant with RIA. Specific antibodies to chemokine receptors were used to block degranulation. RESULTS: Calcium influx was induced by monocyte chemotactic protein (MCP) 1, MCP-3, MCP-4, RANTES, eotaxin, IL-8, and stromal cell-derived factor 1alpha, which are chemokines that bind several chemokine receptors. However, degranulation was induced only by CCR3 ligands, including MCP-3, MCP-4, RANTES, and eotaxin. Priming of eosinophils with IL-5 enhanced CCR3 ligand-induced degranulation but did not cause non-CCR3 ligands to induce eosinophil-derived neurotoxin release. An antibody against CCR3 significantly inhibited degranulation induced by CCR3 ligands, eotaxin, or RANTES. CONCLUSION: These results suggest that chemokine-induced eosinophil degranulation, a major effector of eosinophil functions, is mediated through only CCR3, although some non-CCR3 ligands induce calcium influx in eosinophils. CCR3 may be an important target in the treatment of eosinophilic inflammation.     

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

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

CXCR4 and CCR5 expression by H9 T-cells is downregulated by a peptide-nucleic acid immunomodulator

Product R (Reticulose(TM)) is a peptide-nucleic acid immunomodulator with broad-spectrum antiviral activity that was recently shown to increase expression of mRNAs encoding the proinflammatory cytokines, IFN-gamma, IL-1beta, IL-6 and TNF-alpha. Since these cytokines induce expression of the chemokines, MIP-1alpha, MIP-1beta, RANTES, and SDF-1, all of which inhibit viral infectivity, we were interested to determine if Product R also alters chemokine expression. In addition, the finding, that Product R decreases HIV-1 RNA and extracellular p24 antigen in H9 T-lymphoma cells, suggested to us that this drug may block viral infection by reducing the expression of chemokine receptors on target cells. We have therefore utilized H9 cells to test the effects of Product R on expression of mRNAs encoding the chemokine receptors, CD4, CXCR4 and CCR5, as well as their ligands, IL-16, SDF-1, MIP-1alpha, MIP-1beta, and RANTES, by RT-PCR. We also assayed the effect of Product R on surface receptor expression by flow cytometry, and on the chemotactic activity of these cells towards the CXCR4 ligand, SDF-1, and the CCR5 ligands, MIP-1alpha and RANTES. H9 cells were cultured for 3-21 days in medium containing 5% or 10% Product R, or 5% or 10% PBS. We found that, compared to control cultures, cells cultured in media containing Product R expressed lower amounts of CXCR4 and CCR5 mRNA and surface antigen at all time points. Culture for 3 days in media containing Product R also reduced the ability of cells to migrate towards 10-20 ng/ml SDF-1 and 100-250 ng/ml RANTES. In contrast, Product R had no effect on the expression of CD4 mRNA and receptor protein, or on expression of IL-16 mRNA. These findings suggest that Product R may have clinical efficacy in HIV-1-infected patients by downregulating viral coreceptors on target T-cells.     

Downregulation of CXCR6 and CXCR3 in lymphocytes from birch-allergic patients

Preferential expression of chemokine receptors on Th1 or Th2 T-helper cells has mostly been studied in cell lines generated in vitro or in animal models; however, results are less well characterized in humans. We determined T-cell responses through chemokine receptor expression on lymphocytes, and cytokine secretion in plasma from birch-allergic and healthy subjects. The expression of CCR2, CCR3, CCR4, CCR5, CCR7, CXCR3, CXCR4, CXCR6, IL-12 and IL-18R receptors was studied on CD4⁺ and CD8⁺ cells from birch-allergic ( n  = 14) and healthy ( n  = 14) subjects by flow cytometry. The concentration of IL-4, IL-5, IL-10, IL-12, IFN-γ and TNF-α cytokines was measured in plasma from the same individuals using a cytometric bead array human cytokines kit. The similar expression of CCR4 in T cells from atopic and healthy individuals argues against the use of the receptor as an in vivo marker of Th2 immune responses. Reduced percentages of CD4⁺ cells expressing IL-18R, CXCR6 and CXCR3 were found in the same group of samples. TNF-α, IFN-γ, IL-10, IL-5, IL-4 and IL-12 cytokines were elevated in samples from allergic individuals. Reduced expression of Th1-associated chemokine receptors together with higher levels of Th1, Th2 and anti-inflammatory cytokines in samples from allergic patients indicate that immune responses in peripheral blood in atopic diseases are complex and cannot be simplified to the Th1/Th2 paradigm. Not only the clinical picture of atopic diseases but also the clinical state at different time points of the disease might influence the results of studies including immunological markers associated with Th1- or Th2-type immune responses.     

Regulation of cytokine expression and leukotriene formation in human basophils by growth factors,chemokines and chemotactic agonists

Basophils stimulated with IL-3 plus C5a selectively express IL-4 and IL-13 and continuously produce leukotrienes (LT) for hours. C5a combined with IL-5 or granulocyte-macrophage colony-stimulated factor was, however, much less effective in promoting cytokine expression and a late continuous phase of LTC4 production, possibly due to lower expression levels of their receptor α chains. Basophils also express several chemoattractant receptors, including high levels of C5a receptors, macrophage chemotactic protein (MCP) receptors (CCR2) and eotaxin receptors (CCR3), intermediate levels of CXCR1, CXCR2 and platelet-activating factor receptors, and lower levels of N-formyl-Met-Leu-Phe (fMLP) receptors. However, among the corresponding agonists, only C5a, fMLP and much more weakly MCP-1, were found to induce cytokine expression and continuous LTC4 release, and only when combined with IL-3. CCR3, which is highly expressed on basophils and has been shown to mediate strong migratory but weak release responses, does not regulate cytokine expression. The weakly expressed fMLP receptor is an efficient activator of several cell functions including LTC4 formation, while CXCR2 hardly affects basophil function despite considerable expression. Thus, chemoattractant-receptors mediate different cellular responses unrelated to their expression levels.     

Switch in chemokine receptor expression upon TCR stimulation reveals novel homing potential for recently activated T cells.

When naive T lymphocytes are activated and differentiate into memory/effector cells, they down-regulate receptors for constitutive chemokines such as CXCR4 and CCR7 and acquire receptors for inflammatory chemokines such as CCR3, CCR5 and CXCR3, depending on the Th1/Th2 polarization. This switch in chemokine receptor usage leads to the acquisition of the capacity to migrate into inflamed tissues. Using RNase protection assays, staining with specific antibodies, and response to recombinant chemokines, we now show that following TCR stimulation, memory/effector T cells undergo a further and transient switch in receptor expression. CCR1, CCR2, CCR3, CCR5, CCR6 and CXCR3 are down-regulated within 6 h, while CCR7, CCR4, CCR8 and CXCR5 are up-regulated for 2 to 3 days. Up-regulation of CCR7 following TCR stimulation was observed also among resting peripheral blood T cells and required neither co-stimulation nor exogenous IL-2. On the other hand IL-2 down-regulated CXCR5, up-regulated CCR8 and facilitated the recovery of CCR3 and CCR5. Upon TCR stimulation, Th1 and Th2 cells produced comparable sets of chemokines, including RANTES, macrophage inflammatory protein-1beta, I-309, IL-8 and macrophage-derived chemokine, which may modulate surface chemokine receptors and contribute to cell recruitment at sites of antigenic recognition. Altogether these results show that following TCR stimulation effector/memory T cells transiently acquire responsiveness to constitutive chemokines. As a result, T cells that are activated in tissues may either recirculate to draining lymph nodes or migrate to nearby sites of organized ectopic lymphoid tissues.     

Abnormal expression of chemokine receptors in Behçet's disease: relationship to intracellular Th1/Th2 cytokines and to clinical manifestations

Dynamic interplay between cytokines and chemokines directs trafficking of peripheral blood mononuclear cells to tissues in autoimmune and/or viral diseases. The aim of the current study was to define the expression on CD3+ T cells of six chemokine receptors associated with inflammatory sites and the expression of intracellular cytokines, such as interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), in Behcet's disease (BD). Flow cytometry was used to detect chemokine receptor and intracytoplasmic cytokines' expression. We observed that CD3+ T cells in the peripheral blood express a restricted array of inflammatory chemokine receptors, specifically, CCR5, CCR6 and CXCR3, but little CCR1-3. The highest expression of CXCR3 on CD3+ T cells is associated with the presence of central nervous system (CNS) manifestations or pulmonary involvement. CXCR3 is the principal inflammatory chemokine receptor involved in BD. CCR5 chemokine receptor is increased in BD regardless of clinical manifestations. The frequency of IFN-gamma-producing cells expressing CXCR3+ CD3+ cells is significantly increased in patients with BD compared with normal controls. IL-4-producing cells are decreased in BD. These results demonstrate the predominance of type 1 cytokine producing cells in CXCR3+ CD3+ T cells during BD. We hypothesize that CXCR3 is the principal inflammatory chemokine receptor involved in BD, particularly during CNS and pulmonary manifestations.     

Progenitor egress from the bone marrow after allergen challenge: role of stromal cell-derived factor 1alpha and eotaxin

BACKGROUND: CCR3 expression on CD34+ cells mediates migration to eotaxin in vitro. CXCR4 and stromal cell-derived factor (SDF)-1alpha are important for stem cell homing to hemopoietic compartments. OBJECTIVE: To study chemokine-mediated progenitor cell traffic in allergic inflammation. METHODS: Bone marrow (BM) aspirates were obtained at baseline from normal subjects; atopic subjects without asthma; and subjects with asthma before, 5 hours after, and 24 hours after allergen inhalation (dual and early responders). Changes in chemokine receptor expression and migration were assessed. RESULTS: Expression of CXCR4, but not CCR3, on BM CD34+ cells was greater in normal subjects compared with atopic subjects with asthma. Likewise, SDF-1alpha, but not eotaxin, stimulated a greater migrational response by BM CD34+ cells from normal subjects compared with subjects with asthma. For all subjects, a positive correlation was found between intensity of CXCR4 expression and magnitude of CD34+ cell response to SDF-1alpha. Allergen inhalation attenuated both intensity of CXCR4 expression and SDF-1alpha levels in marrow from dual compared with early responders 24 hours postallergen. In contrast, the intensity of CCR3 expression on BM CD34+ cells increased in dual compared with early responders at 24 hours postallergen. In addition, an increase in migrational responsiveness of BM CD34+ cells to eotaxin and a decrease to SDF-1alpha 24 hours postallergen was found in dual responder subjects with asthma. CONCLUSION: After allergen inhalation in subjects with asthma, a downregulation in CXCR4 intensity on BM CD34+ cells and a reduction in BM SDF-1alpha levels may reduce progenitor retention to marrow stroma promoting peripheral egress, possibly mediated by the CCR3/eotaxin axis.     

Differential regulation of CXCR4 and CCR5 expression by interleukin (IL)-4 and IL-13 is associated with inhibition of chemotaxis and human immunodeficiency Virus (HIV) type 1 replication but not HIV entry into human monocytes

Chemokine receptors CXCR4 and CCR5 play a key role in Human Immunodeficiency Virus (HIV) entry into CD4+ monocytic cells. Alteration in the expression levels of these receptors by immunoregulatory cytokines may influence viral entry and hence susceptibility to HIV infection, viral tropism, and disease progression. Helper T cell type 2 (Th2) cytokines interleukin (IL)-4 and IL-13, which share a subunit of their receptor components and exhibit similar biological effects, have been shown to play a key role in HIV infection and disease progression. In this study, we investigated the effects of IL-4 and IL-13 on the expression of CXCR4 and CCR5, and the biological implications of alteration of CXCR4 and CCR5 regulation on monocytic cells with respect to their migration in response to chemokines, HIV entry, and its replication. The results suggest that both IL-4 and IL-13 inhibited the expression of CXCR4, in contrast to CCR5, which was inhibited by IL-13 alone. The downregulation of CXCR4 and CCR5 was correspondingly associated with the inhibition of their respective ligand-induced chemotaxis. Although IL-13 inhibited the expression of both CXCR4 and CCR5, this downregulation of chemokine receptor expression was not sufficient to prevent virus entry. Furthermore, both IL-4 and IL-13 inhibited viral replication in monocytic cells, suggesting that inhibition of chemokine receptor expression per se by these cytokines may not be sufficient to prevent virus entry, and indicating these cytokines may be inhibiting viral replication by targeting pathways subsequent to virus entry.     

Dysregulation of the IgE/Fc epsilon RI network in HIV-1 infection

Serum IgE levels are increased in adults and children with HIV-1 infection and could be a marker of poor prognosis. Allergic reactions and adverse reactions to drugs are also increased in HIV-1-infected individuals. An imbalance between a T(H)1-like and a T(H)2-like cytokine profile has been documented in HIV-1 infection. We have found that HIV-1 gp120 from different clades is a potent stimulus for histamine and cytokine (IL-4 and IL-13) release from basophils. Gp120 acts as a viral superantigen, interacting with the V(H)3 region of IgE to induce mediator release from human Fc epsilon RI(+) cells. Human basophils and mast cells express the chemokine receptor CCR3, which binds the chemokines eotaxin and RANTES. By interacting with the CCR3 receptor on Fc epsilon RI(+) cells, HIV-1 Tat protein is a potent chemoattractant for human basophils and lung mast cells. Tat protein also induced IL-4 and IL-13 release from basophils. Preincubation of basophils with Tat protein upregulated the surface expression of the CCR3 receptor. Extracellular Tat can influence the directional migration of human Fc epsilon RI(+) cells, the expression of chemokine receptor CCR3, and the release of T(H)2 cytokines. Because Tat protein is actively released by HIV-1-infected cells, our results indicate a novel mechanism by which Fc epsilon RI(+) cells are rendered more susceptible to infection with CCR3-tropic HIV-1 isolates; that is, two HIV-1 proteins, gp120 and Tat, trigger the release of cytokines critical for T(H)2 polarization from Fc epsilon RI(+) cells, and Tat upregulates beta-chemokine receptor CCR3 on these cells.     

Mechanisms of IgE elevation in HIV-1 infection

Serum IgE levels are high in adults and children with HIV-1 infection and could be a marker of poor prognosis. Allergic reactions and adverse reactions to drugs also tend to increase in HIV-1-infected individuals. An imbalance between a "T(H)1-like" and a "T(H)2-like" cytokine profile has been documented in HIV-1 infection. We have demonstrated that HIV-1 gp 120 from different clades is a stimulus for histamine and cytokine (IL-4 and IL-13) release from basophils. Gp 120 acts as a viral superantigen, interacting with the V(H)3 region of IgE to induce mediator release from human Fc epsilonRI+ cells. Human basophils and mast cells express the chemokine receptor CCR3, which binds the chemokines eotaxin and RANTES. By interacting with the CCR3 receptor on Fc epsilonRI+ cells, HIV-I Tat protein is a potent chemoattractant for human basophils and lung mast cells. Preincubation of basophils with Tat protein upregulates mRNA CCR3 and the surface expression of this chemokine receptor. Tat also induces IL-4 and IL-13 release from basophils. Extracellular Tat can influence the directional migration of human Fc epsilonRI+ cells, the expression of chemokine receptor CCR3, and the release of T(H)2 cytokines. Our results indicate two novel mechanisms by which two HIV-1 proteins, gp120 and Tat, trigger the release of cytokines critical for T(H)2 polarization from human Fc epsilonRI+ cells.     

Assessment of chemokine receptor expression by human Th1 and Th2 cells in vitro and in vivo.

The preferential association of some chemokine receptors with human Th1 or Th2 cells has recently been reported. In this study, the expression of CCR3, CCR5, CXCR3, and CXCR4 were analyzed by flow cytometry in three distinct in vitro models of Th1/Th2 polarization, activated naive and memory T cells, and T-cell clones, in which the intracellular synthesis of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) and the surface expression of CD30 and LAG-3 were also assessed. Moreover, by using immunohistochemistry the in vivo expression of CCR3, CCR5, CXCR3, and CXCR4 was examined in the gut of patients suffering from Crohn's disease, a Th1-dominated disorder, and in the skin of patients suffering from systemic sclerosis, a Th2-dominated disorder. CCR5 and LAG-3 exhibited the same pathway of Th1 association, whereas CXCR3 did not discriminate between Th1- and Th2-dominated responses. On the other hand, CCR3 was found only occasionally in a small proportion of allergen-specific memory T cells with Th2/ThO profile of cytokine production in vitro. However, it was neither seen in Th2-polarized activated naive T cells nor in established Th2 clones and could be detected in vivo only on non-T cells. Finally, whereas CXCR4 expression was not limited to Th2 cells in vivo, it was markedly up-regulated by IL-4 and down-regulated by IFN-gamma in vitro. Thus, the results of this study confirm the existence of flexible programs of chemokine receptor expression during the development of Th1 and Th2 cells. However, caution is advised in interpreting these receptors as surrogate markers of a given type of effector response.     

Lack of correlation between chemokine receptor and T(h)1/T(h)2 cytokine expression by individual memory T cells

Chemokine and chemokine receptor interactions may have important roles in leukocyte migration to specific immune reaction sites. Recently, it has been reported that CXC chemokine receptor (CXCR) 3 and CC chemokine receptor (CCR) 5 were preferentially expressed on T(h)1 cells, and CCR3 and CCR4 were preferentially expressed on T(h)2 cells. To investigate chemokine receptor expression by T(h) subsets in vivo, we analyzed cytokine (IL-2, IL-4 and IFN-gamma) and chemokine receptor (CXCR3, CXCR4, CCR3, CCR4 and CCR5) mRNA expression by individual peripheral CD4(+) memory T cells after short-term stimulation, employing a single-cell RT-PCR method. This ex vivo analysis shows that the frequencies of cells expressing chemokine receptor mRNA were not significantly different between T(h)1 and T(h)2 cells in normal peripheral blood. To assess a potential role of in vivo stimulation, we also analyzed unstimulated rheumatoid arthritis synovial CD4(+) memory T cells. CXCR3, CXCR4, CCR3 and CCR5 expression was detected by individual synovial T cells, but the frequencies of chemokine receptor mRNA were not clearly different between T(h)1 and non-T(h)1 cells defined by expression of IFN-gamma or lymphotoxin-alpha mRNA in all RA patients. These data suggest that chemokine receptor expression does not identify individual memory T cells producing T(h)-defining cytokines and therefore chemokine receptor expression cannot be a marker for T(h)1 or T(h)2 cells in vivo.     

Functional inhibition of CCR3-dependent responses by peptides derived from phage libraries.

So far chemokine antagonists have been identified by modification of the NH2-terminus of known chemokines or by screening large number of compounds in functional assays. Here we used phage display peptide libraries to identify hexapeptides that antagonize the interaction between eotaxin and its receptor CCR3. The peptide sequence CPWYFWPC was recovered by panning phage libraries on CCR3-transfected murine pre-B cells after elution with eotaxin. The synthetic, structurally constrained peptide effectively competed 125I-eotaxin binding to CCR3 (IC(50) = 20 microM). Furthermore, it had weak agonistic effects on Ca(2+) mobilization in CCR3 transfectants that underwent heterologous desensitization by subsequent exposure to eotaxin. The peptide inhibited chemotaxis of CCR3 transfectants induced by a broad panel of CCR3 ligands. Specificity was tested with the CXCR1, CXCR2, CXCR3 and CCR5 receptors. In experiments aimed at characterization of residues necessary for eotaxin binding, we affinity purified the linear eotaxin-binding peptide VTPRQR, and showed that the peptide displaced the binding of radiolabeled eotaxin to CCR3 (IC(50) = 300 microM) ina dose-dependent manner, inhibited eotaxin induced increases in intracellular Ca(2+), and migration of CCR3-transfected cells. Specificity was affirmed using other CCR3 ligands. This is the first de novo identification of chemokine antagonists by direct screening on target proteins.     

Kinetics and expression patterns of chemokine receptors in human CD4+ T lymphocytes primed by myeloid or plasmacytoid dendritic cells

We investigated the kinetics of expression of 12 chemoattractant receptors as a function of cell division following priming of human naive CD4+ T cells by different populations of dendritic cells (DC) and under conditions favoring Th1 or Th2 differentiation. Two chemokine receptors, CXCR3 and CXCR5, were rapidly up-regulated following T cell activation by either monocyte-derived DC, myeloid DC (mDC) or plasmacytoid DC (pDC). While CXCR5 expression was transient, expression of CXCR3 at advanced cell divisions was dependent on differentiation, being expressed at high levels on Th1 cells. Several other receptors (CCR2, CCR3, CCR4, CCR5, CXCR6 and CRTh2) were acquired progressively as a function of cell division and in a fashion that was influenced by polarizing cytokines. The Th2-associated chemoattractant receptors CRTh2 and CCR3 were up-regulated with slower kinetics compared to the Th1-associated receptors CXCR3 and CXCR6, consistent with a different kinetics and efficiency of polarization. Moreover, CCR4 and CXCR6 were preferentially induced in T cells activated by mDC and pDC, respectively. Finally, CXCR5 and CCR7 were also rapidly and transiently up-regulated in memory T cells following TCR stimulation. These results indicate a complex chemokine receptor regulation dependent on both T cell activation and differentiation state. In addition, they reveal the existence of DC-specific cues for the regulation of T cell migratory capacity.     

Neuroinflammation in Alzheimer’s disease: chemokines produced by astrocytes and chemokine receptors

Chemokines secreted by astrocytes play multiple roles in the pathology of Alzheimer’s disease, a chronic inflammation disorder of central nervous system. The level of chemokines in serum, cerebrospinal fluid and brain tissue and their receptors both significantly changed in patients with Alzheimer’s disease. In this review, we briefly summarized the involvement of astrocytes and chemokines in Alzheimer’s disease, and the role of chemokine/chemokine receptors in the occurrence and development of Alzheimer’s disease. Clarification of the involvement of chemokines and their receptors, such as MCP-1/CCR2, fractalkine/CX3CR1, SDF-1α/CXCR4, MIP-1α/CCR5, IP-10/CXCR3, IL-8/CXCR1, CXCR2, and RANTES/CCR1, CCR3, CCR5, will provide a new strategy and more specific targets for the treatment of Alzheimer’s disease.     

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

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

Clonal Th2 cells associated with chronic hypereosinophilia: TARC-induced CCR4 down-regulation in vivo

We analyzed the expression of chemokine receptors on clonal Th2-type CD4(+)CD3(- )lymphocytes isolated from blood of two patients with chronic hypereosinophilia. First, we observed that these Th2 cells express membrane CCR5 and CXCR4 but neither CCR3 nor CCR4 when analyzed immediately after purification. However, CCR4 appeared following culture in human serum-free medium, suggesting that it was down-regulated in vivo. Indeed, patient's serum, but not control human serum, strongly down-regulated CCR4 expression on cultured Th2 cells. As high levels of TARC, a CCR4 ligand, were detected in the serum of four hypereosinophilic patients with CD3(-)CD4(+) clonal Th2 cells, we evaluated the effect of TARC neutralization in this system. Addition of a neutralizing anti-TARC mAb inhibited CCR4 down-regulation by patient's serum, indicating that circulating TARC contributed to CCR4 down-regulation on Th2 cells in vivo. Clonal Th2 cells did not secrete high levels of TARC themselves but induced a sustained production of TARC by monocyte-derived dendritic cells, a phenomenon that was inhibited by addition of blocking mAb against IL-4 receptor. We conclude that high circulating levels of TARC in serum of patients with chronic hypereosinophilia, most likely derived from antigen-presenting cells stimulated by Th2-type cytokines, induce down-regulation of CCR4 on Th2 cells in vivo.