The effects of a CCR3 inhibitor, AXP1275, on allergen-induced airway responses in adults with mild-to-moderate atopic asthma

BACKGROUND

CCR3 is the cognate receptor for major human eosinophil chemoattractants from the eotaxin family of proteins that are elevated in asthma and correlate with disease severity.

OBJECTIVE

This proof-of-mechanism study examined the effect of AXP1275, an oral, small-molecule inhibitor of CCR3, on airway responses to inhaled allergen challenge.

METHODS

Twenty-one subjects with mild atopic asthma and documented early and late asthmatic responses to an inhaled aeroallergen completed a randomized double-blind cross-over study to compare early and late allergen-induced asthmatic responses, methacholine PC₂₀ , blood and sputum eosinophils and exhaled nitric oxide after 2 weeks of treatment with once-daily doses of AXP1275 (50 mg) or placebo.

RESULTS

There was a significant increase in methacholine PC₂₀ after 12 days of AXP1275 treatment compared to placebo (increase of 0.92 doubling doses versus 0.17 doubling doses, P = .01), but this protection was lost post-allergen challenge. There was no effect of AXP1275 on allergen-induced late asthmatic responses, or eosinophils in blood and sputum. The early asthmatic response and exhaled nitric oxide levels were slightly lower with AXP1275, but this did not reach statistical significance. The number of subjects who experienced treatment-emergent adverse events while receiving AXP1275 was comparable placebo.

CONCLUSIONS & CLINICAL RELEVANCE

AXP1275 50 mg administered daily was safe and well tolerated, and there was no difference in the type, severity or frequency of treatment-emergent adverse events in subjects while receiving AXP1275 compared to placebo. AXP1275 increased the methacholine PC₂₀ ; however, the low and variable exposure to APX1275 over a short treatment period may have contributed to poor efficacy on other outcomes.

Cockroach allergen extract stimulates protease-activated receptor-2 (PAR-2) expressed in mouse lung fibroblast

OBJECTIVE

To investigate whether cockroach allergen extract can stimulate Protease-activated receptor 2 (PAR-2) expressed in mouse lung fibroblast.

MATERIALS

We established an immortalized lung fibroblast cell line, DM5, from PAR-2 deficient mice. By stable transfection with either an empty vector (DM5/EV) or an expression vector encoding mouse PAR-2 cDNA (DM5/Par2), a pair of lung fibroblast cell lines with or without functional PAR-2 expression were prepared.

TREATMENT

The cells were exposed to cockroach allergen extract [up to 800 protein nitrogen unit (PNU)/ml], trypsin (up to 100 nM), SLIGRL agonist peptide (up to 500 microM), and trans-cinnamoyl-LIGRO agonist peptide (up to 400 microM).

METHODS

The cells were loaded with Fluo-3 calcium indicator and mobilization of intracellular calcium with the stimuli was monitored by a fluorometric plate reader. Extracellular signal-regulated kinase (ERK) phosphorylation was examined by Western blot analysis using an anti-phospho ERK antibody.

RESULTS

The cockroach extract induced intracellular calcium transients in a concentration dependent manner in DM5/Par2 but not in DM5/EV. The activity was abolished when the cockroach extract was heat denatured or pre-incubated with PMSF (phenylmethanesulfonyl fluoride) prior to the assay. Concomitantly, ERK phosphorylation was seen in DM5/Par2 with the cockroach extract but not with a heat-denatured extract. The responses were sensitive to an inositol-1,4,5 triphosphate antagonist (2-APB) indicating that calcium was mobilized from intracellular store.

CONCLUSIONS

Cockroach allergen extract can activate PAR-2 and thereby stimulate mouse lung fibroblasts likely through protease(s). The present study proposes a potential mechanism for cockroach antigens, similar to house dust mite antigens, in the etiology of respiratory diseases.

Differential modulation of human basophil functions through prostaglandin D2 receptors DP and chemoattractant receptor-homologous molecule expressed on Th2 cells/DP2

BACKGROUND

Both prostaglandin (PG) D receptor (DP) and CRTH2 (chemoattractant receptor-homologous molecule expressed on Th2 cells)/DP2 are high-affinity receptors for PGD2. Previous studies have demonstrated that PGD2 enhances releasability and induces CRTH2/DP2-mediated migration in human basophils, but the precise effects of PGD2 on basophils as well as receptor usage have not been fully clarified.

OBJECTIVE

We comprehensively explored the roles of DP and CRTH2/DP2 in basophil functions by using selective agonists and antagonists for each receptor.

METHODS

DP and CRTH2/DP2 transcripts were quantified by real-time PCR. We studied the effects of selective agonists (DP: BW245C; CRTH2/DP2: 13,14-dihydro-15-keto (DK)-PGD2) and/or antagonists (DP: BWA868C; CRTH2/DP2: ramatroban) on Ca2+ mobilization, migration, degranulation, CD11b expression and survival of human basophils.

RESULTS

Basophils expressed transcripts of both DP and CRTH2/DP2, but the levels of CRTH2/DP2 transcripts were ca. 100-fold higher compared with DP transcripts. Ca2+ influx was induced in basophils by either PGD2 or DK-PGD2/CRTH2 agonist but not by BW245C/DP agonist. Basophils treated with PGD2 were completely desensitized to subsequent stimulation with DK-PGD2, but not vice versa. DK-PGD2 as well as PGD2 up-regulated CD11b expression, induced migration and enhanced degranulation, and those effects were completely antagonized by ramatroban/CRTH2 antagonist. In contrast, BW245C/DP agonist exhibited an inhibitory effect on basophil migration and IgE-mediated degranulation, and the migration inhibitory effect was effectively antagonized by BWA868C/DP antagonist. On the other hand, while PGD2 significantly shortened the basophil life-span, neither DK-PGD2/CRTH2 agonist nor BW245C/DP agonist did.

CONCLUSION

CRTH2/DP2 is primarily responsible for the pro-inflammatory effects of PGD2 on human basophils, while DP introduces negative signals capable of antagonizing the effects of CRTH2/DP2 in these cells. The effects of PGD2 on longevity imply a mechanism(s) other than via DP or CRTH2/DP2. CRTH2/DP2 on basophils may afford opportunities for therapeutic targeting in allergic inflammation.

Molecular cloning and functional characterization of Cynomolgus monkey (Macaca fascicularis) CC chemokine receptor, CCR3

We have cloned and performed the first functional characterization of the chemokine receptor, CCR3, of Cynomolgus monkey (Macaca fascicularis). The deduced amino acid sequence of the cloned Cynomolgus CCR3 was found to be more similar to that of a previously-reported Rhesus (Macaca mulatta) CCR3 (99.4%) than that of a reported Cynomolgus CCR3 (98.0%). Stably-transfected Cynomolgus CCR3 bound human eotaxin (CCL11) with similar kinetics (Kd 240 pM) and was responsive to human CCR3 ligands (eotaxin [CCL11], eotaxin-2 [CCL24], and MCP4 [CCL13]) in Ca(2+) mobilization and chemotaxis assays, thus provides a useful alternative species model system for the analysis of modulators of eotaxin--CCR3 induced signaling and activation.

Molecular determinants of receptor binding and signaling by the CX3C chemokine fractalkine

Fractalkine/CX3CL1 is a membrane-tethered chemokine that functions as a chemoattractant and adhesion protein by interacting with the receptor CX3CR1. To understand the molecular basis for the interaction, an extensive mutagenesis study of fractalkine's chemokine domain was undertaken. The results reveal a cluster of basic residues (Lys-8, Lys-15, Lys-37, Arg-45, and Arg-48) and one aromatic (Phe-50) that are critical for binding and/or signaling. The mutant R48A could bind but not induce chemotaxis, demonstrating that Arg-48 is a signaling trigger. This result also shows that signaling residues are not confined to chemokine N termini, as generally thought. F50A showed no detectable binding, underscoring its importance to the stability of the complex. K15A displayed unique signaling characteristics, eliciting a wild-type calcium flux but minimal chemotaxis, suggesting that this mutant can activate some, but not all, pathways required for migration. Fractalkine also binds the human cytomegalovirus receptor US28, and analysis of the mutants indicates that US28 recognizes many of the same epitopes of fractalkine as CX3CR1. Comparison of the binding surfaces of fractalkine and the CC chemokine MCP-1 reveals structural details that may account for their dual recognition by US28 and their selective recognition by host receptors.

The neuronal repellent Slit inhibits leukocyte chemotaxis induced by chemotactic factors

Migration is a basic feature of many cell types in a wide range of species. Since the 1800s, cell migration has been proposed to occur in the nervous and immune systems, and distinct molecular cues for mammalian neurons and leukocytes have been identified. Here we report that Slit, a secreted protein previously known for its role of repulsion in axon guidance and neuronal migration, can also inhibit leukocyte chemotaxis induced by chemotactic factors. Slit inhibition of the chemokine-induced chemotaxis can be reconstituted by the co-expression of a chemokine receptor containing seven transmembrane domains and Roundabout (Robo), a Slit receptor containing a single transmembrane domain. Thus, there is a functional interaction between single and seven transmembrane receptors. Our results reveal the activity of a neuronal guidance cue in regulating leukocyte migration and indicate that there may be a general conservation of guidance mechanisms underlying metazoan cell migration. In addition, we have uncovered an inhibitor of leukocyte chemotaxis, and propose a new therapeutic approach to treat diseases involving leukocyte migration and chemotactic factors.

The chemokine fractalkine inhibits Fas-mediated cell death of brain microglia

Fractalkine is a CX3C-family chemokine, highly and constitutively expressed on the neuronal cell surface, for which a clear CNS physiological function has yet to be determined. Its cognate receptor, CX3CR-1, is constitutively expressed on microglia, the brain-resident macrophages; however, these cells do not express fractalkine. We now show that treatment of microglia with fractalkine maintains cell survival and inhibits Fas ligand-induced cell death in vitro. Biochemical characterization indicates that this occurs via mechanisms that may include 1) activation of the phosphatidylinositol-3 kinase/protein kinase B pathway, resulting in phosphorylation and blockade of the proapoptotic functions of BAD; 2) up-regulation of the antiapoptotic protein Bcl-xL; and 3) inhibition of the cleavage of BH3-interacting domain death agonist (BID). The observation that fractalkine serves as a survival factor for primary microglia in part by modulating the protein levels and the phosphorylation status of Bcl-2 family proteins reveals a novel physiological role for chemokines. These results, therefore, suggest that the interaction between fractalkine and CX3CR-1 may play an important role in promoting and preserving microglial cell survival in the CNS.

Chemokine receptor antagonism as a new therapy for multiple sclerosis

New information about the role of tissue inflammation in the pathogenesis of multiple sclerosis (MS) has driven a search for effective and specific therapeutics that address leukocyte trafficking. These developments in understanding MS are complemented by advances in clarifying the molecular mechanisms of leukocyte extravasation and providing the knowledge base needed to modulate tissue inflammation. Of particular interest are the chemokines and their receptors. Chemokines constitute a large family of chemoattractant peptides that regulate the vast spectrum of leukocyte migration events. This review discusses MS and proposes that identifying the chemokines and receptors involved in the inflammation associated with this disorder may lead to therapeutic intervention.

Chemokines and their receptors in neurobiology: perspectives in physiology and homeostasis

Chemokines are a large family of small secreted proteins (8-14 kDa) associated with the trafficking of leukocytes in physiological immunosurveillance as well as inflammatory cell recruitment in different disease processes. A limited repertoire of chemokines and their specific cognate receptors are detectable in cells of the CNS such as microglia, astrocytes and neurons under physiological conditions. Coupled with distinct patterns of ligand and receptor expression in various pathologies including multiple sclerosis, trauma, neuro-AIDS, Alzheimer's disease, stroke, neuro- and glioblastomas, such phenomena have fueled the strong belief that chemokines must fulfill significant and potentially diverse functional roles in the CNS.

NF-kappaB-dependent fractalkine induction in rat aortic endothelial cells stimulated by IL-1beta, TNF-alpha, and LPS

Fractalkine is an endothelial cell-derived CX3C chemokine that is chemotactic mainly to mononuclear cells. Fractalkine was induced in rat aortic endothelial cells (RAEC) by interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), and lipopolysaccharide (LPS) transcriptionally and translationally. This induction correlated with increased NF-kappaB DNA binding activity as determined by gel mobility shift assay. Supershift assays revealed that the NF-kappaB subunits p50 and p65 were responsible for kappaB binding. Accordingly, we examined the role of NF-kappaB in fractalkine induction in RAEC through the use of an adenovirus-mediated mutant IkappaB as a specific inhibitor. Delivery of a dominant-negative form of IkappaBalpha in RAEC dramatically reduced the induction of fractalkine by these stimuli, suggesting a role for NF-kappaB activation in fractalkine induction. The inhibition of fractalkine expression by two potent NF-kappaB inhibitors, sulfasalazine and sanguinarine, further supported the central role of NF-kappaB in fractalkine transcription regulation and suggested a novel therapeutic target aimed at modulating leukocyte endothelial cell interaction.

Pharmacological and signaling analysis of human chemokine receptor CCR-7 stably expressed in HEK-293 cells: high-affinity binding of recombinant ligands MIP-3beta and SLC stimulates multiple signaling cascades

The chemokine receptor CCR-7 is expressed in T, NK, and dendritic cells in a time-ordered and stimulus-dependent manner. Thorough analyses of the pharmacological profiles of the recombinant ligands for CCR-7, MIP-3beta/ELC/CK-beta 11, and SLC/Exodus-2/TCA4/6C-kine, using CCR-7-expressing HEK-293E transfectants determine that ligands both bind with a K(d) in the 100 pM range-10- to 100-fold greater affinities than published K(d) values. High-affinity binding of each ligand is associated with rapid mobilization of intracellular calcium and cell migration as predicted for chemokine GPCRs, and in keeping with more recent evidence, robust activation of mitogen-activated protein kinase (MAPK).

MIP-3alpha induces human eosinophil migration and activation of the mitogen-activated protein kinases (p42/p44 MAPK)

The CC chemokine macrophage inflammatory protein-3alpha (MIP-3alpha) is the product of recent electronic cloning efforts, however, little characterization of its spectrum of biological effects has been undertaken. Human eosinophils exhibited pertussis-toxin-sensitive migration in response to human recombinant (hr)MIP-3alpha. Messenger RNA for the MIP-3alpha receptor, CCR-6, and low levels of surface expression were demonstrated by reverse transcriptase-polymerase chain reaction and FACS analysis. Analyses of cell signaling revealed dose-dependent increases in intracellular calcium mobilization, calcium transients that were, however, greatly reduced when compared with MCP-3-induced responses. Further investigations of MIP-3alpha-induced signal transduction revealed time- and dose-dependent, partially pertussis toxin-dependent, increases in phosphorylation of the p42/p44 mitogen-activated protein kinases (MAPK) that occurred at 10- to 100-fold lower concentrations, and that were linked to a phosphoinositide 3-kinase pathway. These results suggest that MIP-3alpha can regulate multiple, parallel signal transduction pathways in eosinophils, and suggest that MAPK activation by MIP-3alpha in eosinophils is a significant signaling pathway for migration induction.

Prevention of crescentic glomerulonephritis by immunoneutralization of the fractalkine receptor CX3CR1 rapid communication

BACKGROUND

Fractalkine is a newly identified T-cell and monocyte/macrophage (Mphi) chemokine with a transmembrane domain and is a cell-surface protein on activated endothelium. It can mediate adhesion of cells expressing the fractalkine receptor CX3CR1. These unique features make fractalkine well suited for leukocyte recruitment in tissues with high blood flow as in the renal glomerulus.

METHODS

Fractalkine expression in glomeruli and response of isolated glomerular inflammatory cells to fractalkine were studied in the Wistar-Kyoto (WKY) crescentic glomerulonephritis model. Antibody was used to confirm the proinflammatory role of fractalkine.

RESULTS

Fractalkine was markedly induced in the endothelium of nephritic rat glomeruli, and inflammatory leukocytes infiltrating the glomeruli expressed increased levels of CX3CR1. Anti-CX3CR1 antibody treatment dramatically blocked leukocyte infiltration in the glomeruli, prevented crescent formation, and improved renal function.

CONCLUSIONS

Fractalkine plays a central role in leukocyte trafficking at the endothelium in the high-flow glomerular circuit and, in turn, implicates CX3CR1 as a prime drug target for therapeutic intervention of endothelium-related inflammatory diseases.

Activation of mitogen-activated protein kinase regulates eotaxin-induced eosinophil migration

Eotaxin is a potent eosinophil chemoattractant that plays an important role in regulating eosinophil tissue levels both in healthy individuals and in diseases associated with significant eosinophil infiltrates, such as the allergic inflammation observed in asthma. Here, we demonstrate that treatment of eosinophils with eotaxin induces the phosphorylation of the mitogen-activated protein kinases (MAPKs) p42 and p44, leading to kinase activation. Blockade of MAPK activation by the MAPK kinase inhibitor PD98059 leads to a dramatic decrease in eotaxin-induced eosinophil rolling in vivo and chemotaxis in vitro. This blockade in the leukocyte migration process is consistent with the observed inhibition of actin polymerization and rearrangement within the eosinophil following treatment with MAPK inhibitor. It is suggested, therefore, that the intrinsic mechanism of eotaxin-induced eosinophil rolling and migration involves activation of the p42/p44 MAPK, possibly through regulation of the cytoskeletal rearrangements necessary for chemotaxis.

Characterization of fractalkine in rat brain cells: migratory and activation signals for CX3CR-1-expressing microglia

Molecular analyses of the chemokine fractalkine and its receptor CX3C-R1 in the rat brain have revealed a striking polarization: fractalkine is expressed constitutively in neurons and is up-regulated by TNF-alpha and IL-1beta in astrocytes. Expression of its specific receptor, CX3C-R1, is restricted to astrocytes and microglia. We have analyzed the functional correlates of this expression and demonstrate that fractalkine induces microglial cell migration and activation. However, the activity of this chemokine on astrocytes may also be highly relevant in inducing astrocyte-microglia cell interactions through cytokine/mediator release leading to microglial activation.

Human thymocytes express CCR-3 and are activated by eotaxin

Eotaxin has been characterized as a chemokine involved in eosinophil activation; however, mRNA for this C-C chemokine has been shown to be constitutively expressed in thymus. Immunohistochemical analysis showed a punctate distribution pattern, with eotaxin expression localized mainly in the medulla and in Hassle's corpuscles. Moreover, the receptor for eotaxin, CCR-3, was detected on thymocytes, with the highest level of expression being on the CD8 single-positive population. Equilibrium binding analyses on unfractionated thymocytes demonstrated specific 125I-eotaxin binding profiles comparable with CCR-3 transfectants. Eotaxin induced cell migration and mobilization of intracellular calcium in all thymocytes except the immature CD4(-)/CD8(-) population. Eotaxin also induced the secretion of the chemokines interleukin-8, RANTES, and macrophage inflammatory protein-1beta from thymocyte cultures in vitro. These results suggest that eotaxin-induced thymocyte activation may have important physiological implications for lymphocyte mobilization within and from this lymphoid organ.

Role for neuronally derived fractalkine in mediating interactions between neurons and CX3CR1-expressing microglia

A recently identified chemokine, fractalkine, is a member of the chemokine gene family, which consists principally of secreted, proinflammatory molecules. Fractalkine is distinguished structurally by the presence of a CX3C motif as well as transmembrane spanning and mucin-like domains and shows atypical constitutive expression in a number of nonhematopoietic tissues, including brain. We undertook an extensive characterization of this chemokine and its receptor CX3CR1 in the brain to gain insights into use of chemokine-dependent systems in the central nervous system. Expression of fractalkine in rat brain was found to be widespread and localized principally to neurons. Recombinant rat CX3CR1, as expressed in Chinese hamster ovary cells, specifically bound fractalkine and signaled in the presence of either membrane-anchored or soluble forms of fractalkine protein. Fractalkine stimulated chemotaxis and elevated intracellular calcium levels of microglia; these responses were blocked by anti-CX3CR1 antibodies. After facial motor nerve axotomy, dramatic changes in the levels of CX3CR1 and fractalkine in the facial nucleus were evident. These included increases in the number and perineuronal location of CX3CR1-expressing microglia, decreased levels of motor neuron-expressed fractalkine mRNA, and an alteration in the forms of fractalkine protein expressed. These data describe mechanisms of cellular communication between neurons and microglia, involving fractalkine and CX3CR1, which occur in both normal and pathological states of the central nervous system.

In vivo inhibition of CC and CX3C chemokine-induced leukocyte infiltration and attenuation of glomerulonephritis in Wistar-Kyoto (WKY) rats by vMIP-II

Chemokines play a central role in immune and inflammatory responses. It has been observed recently that certain viruses have evolved molecular piracy and mimicry mechanisms by encoding and synthesizing proteins that interfere with the normal host defense response. One such viral protein, vMIP-II, encoded by human herpesvirus 8, has been identified with in vitro antagonistic activities against CC and CXC chemokine receptors. We report here that vMIP-II has additional antagonistic activity against CX3CR1, the receptor for fractalkine. To investigate the potential therapeutic effect of this broad-spectrum chemokine antagonist, we studied the antiinflammatory activity of vMIP-II in a rat model of experimental glomerulonephritis induced by an antiglomerular basement membrane antibody. vMIP-II potently inhibited monocyte chemoattractant protein 1-, macrophage inflammatory protein 1beta-, RANTES (regulated on activation, normal T cell expressed and secreted)-, and fractalkine-induced chemotaxis of activated leukocytes isolated from nephritic glomeruli, significantly reduced leukocyte infiltration to the glomeruli, and markedly attenuated proteinuria. These results suggest that molecules encoded by some viruses may serve as useful templates for the development of antiinflammatory compounds.

Chemokines in disease models and pathogenesis

Investigators from a wide variety of disciplines met at the Second National Managed Health Care Congress Meeting on chemokines held in Washington, D.C. on December 14-15, 1997, to discuss the role of chemokines in the pathogenesis of disease states, as well as a number of biological issues. Presentations on the effects of chemokines in animal models were interspersed with talks on fundamental chemokine structure-function relationships, signal transduction, the role of chemokine in cell trafficking, inflammation, immunity and hematopoietic development. Although it was impossible to consider the score of chemokine receptors and the 50 or more chemokines cloned to date, most of the more well established and some of the newer chemokines were discussed. We will first summarize the preconference symposium on the role of chemokines in neurobiology and then review the various issues addressed by the other speakers to provide a more integrated rather than sequential summary of the proceedings.

Molecular cloning and functional characterization of human MIP-1 delta, a new C-C chemokine related to mouse CCF-18 and C10

We have isolated a novel human C-C chemokine, MIP-1 delta from a human fetal spleen cDNA library. The human MIP-1 delta cDNA has an unusually long 400-bp 5-prime untranslated region and a predicted 113-amino acid protein of 10 kDa. The coding sequence contains a signal peptide of 21 amino acids, indicating that the mature protein has 92 amino acids (8 kDa). Recombinant human MIP-1 delta produced by transfected human embryonic kidney 293 cells produced an 8-kDa protein, which confirmed the presence of a signal peptide. Compared with other human C-C chemokines, human MIP-1 delta shows the highest homology with human HCC-1, CK beta-8, murine C10, and CCF18 (MIP-1 gamma). The human MIP-1 delta gene is localized on chromosome 17 where most of the C-C chemokine superfamily is located. Human MIP-1 delta is expressed in T and B lymphocytes, NK cells, monocytes, and monocyte-derived dendritic cells, but not in bone marrow-derived dendritic cells. Its expression can be induced by other proinflammatory cytokines in monocytes and dendritic cells. Human MIP-1 delta is chemotactic for T cells and monocytes, but not for neutrophils, eosinophils, or B cells. Human MIP-1 delta induced calcium flux in human CCR1-transfected cells.

Macrophage inflammatory protein-1beta induces migration and activation of human thymocytes

The CC chemokine macrophage inflammatory protein 1beta (MIP-1beta), has been shown to be a chemoattractant preferentially activating CD4(+) CD45RA+ T lymphocytes. Further analysis of chemokine action on lymphocytic cells has shown the potent migration-promoting capacity of MIP-1beta on human thymocytes. The responding cells were the CD4(+) and CD8(+) single-positive (SP), as well as the CD4(+) CD8(+) double-positive (DP) populations, with little if any migratory activity on the double-negative (DN) population. The activation of thymocytes by MIP-1beta appeared to be a direct, receptor-mediated event as evidenced by the rapid mobilization of intracellular calcium, increase in proteins phosphorylated on tyrosine, and activation of the mitogen-activated protein kinase (MAPK) pathway. Radioligand binding analyses showed specific and displaceable binding of MIP-1beta to thymocytes with a Kd of approximately 1 nmol/L, a profile that was comparable with MIP-1beta binding to CCR-5-transfected NIH 3T3 cells. In addition, CCR-5 mRNA was detected in total thymocyte populations indicating that activation of thymocytes by MIP-1beta may occur through binding to CCR-5. Further dissection of the subpopulations showed that only the DP and CD8(+) SP populations expressed CCR-5 and expression data on these two populations was confirmed using anti-CCR-5 monoclonal antibody. These data may be suggestive of a role for MIP-1beta in human thymocyte activation, and show a potential route for HIV infectivity in the developing immune system.

RANTES activation of phospholipase D in Jurkat T cells: requirement of GTP-binding proteins ARF and RhoA

The chemokine RANTES is a potent agonist of T cell activation. In an investigation of signal-transduction events activated by this chemokine, we have shown that RANTES stimulates dose-dependent phospholipase D (PLD) activity in Jurkat cells. Equilibrium-binding analyses using 125I-labeled RANTES indicated the presence of a receptor for RANTES on these cells, which has a Kd of 0.1 nM, is expressed at approximately 600 sites per cell, and a binding specificity that was not comparable with that of any of the known chemokine receptors, since 125I-labeled RANTES was displaced by macrophage-inflammatory protein-1 beta (but not macrophage-inflammatory protein-1 alpha), monocyte-chemotactic protein-1 (MCP-1), MCP-3, MCP-4, and eotaxin. RANTES-induced PLD activation was augmented by GTP gamma S, but not GDP beta S, and inhibited by the protein kinase C inhibitor bisindolylmaleimide, as well as the fungal metabolite brefeldin A, and C3 exoenzyme (Clostridium botulinum), implicating the activation of RhoA. RANTES also induced GTP-GDP exchange of immunoprecipitated RhoA. RANTES-stimulated PLD activity was dependent on an ADP-ribosylation factor(s), as assessed by inhibition studies using a synthetic inhibitory peptide of the N-terminal 16 amino acids of ADP-ribosylation factor 1. These studies indicate the potential existence of a novel receptor-mediated mechanism for activation of T cells by the chemokine RANTES.

RANTES-induced T cell activation correlates with CD3 expression

The chemokine RANTES induces a unique biphasic cytoplasmic Ca2+ signal in T cells. The first phase of this signal, similar to that of other chemokines, is G-protein mediated and chemotaxis associated. The second phase of this signal, unique to RANTES and evident at concentrations greater than 100 nM, is tyrosine kinase linked and results in a spectrum of responses similar to those seen with antigenic stimulation of T cells. We show here that certain jurkat T cells responded to RANTES solely through this latter pathway. A direct correlation between the RANTES-induced second phase response and CD3 expression was demonstrated in these cells. Sorting the Jurkat cells into CD3(high) and CD3(low) populations revealed that only the CD3(high) cells were responsive to RANTES. Furthermore, stimulation of these Jurkat cells with anti-CD3 mAb significantly depresses their subsequent response to RANTES. While a RANTES-specific chemokine receptor is expressed at a low level on these Jurkat cells, the RANTES-induced activation is dependent on the presence of the TCR. Thus, stimulation through TCR may partially account for RANTES' unique pattern of signaling in T cells.

Primary sensory neurons migrate in response to the chemokine RANTES

We examined the potential for the C-C chemokine RANTES to stimulate dorsal root ganglia (DRG) cell migration. Embryonic day 12 (E12.5) mouse DRG cells migrated in response to RANTES, in vitro, differentiating to the nociceptive phenotype within 18 h. In addition, RANTES stimulated intracellular calcium mobilization in DRG cells. RANTES expression was demonstrated by polymerase chain reaction analysis to be present in E10.5 limb bud, E12.5 DRG, Schwann cells, spinal cord and skin. RANTES protein was detected immunohistochemically in E12.5 DRG and the cutaneous layers of the developing hind limb. Thus, RANTES expression is spatially and temporally consistent with an effector molecule in sensory neuropoiesis, potentially expanding the role of this chemokine to include neurotropism.

Chemokine receptor CCR3 function is highly dependent on local pH and ionic strength

The CC chemokine receptor 3 (CCR3) plays an important role in the regulation of the migration of eosinophils, a leukocyte population involved in many inflammatory pathologies including asthma. CCR3 binds to the CC chemokine eotaxin, a promigratory cytokine originally isolated as the key component in a model of eosinophil-induced airway inflammation. We show here that eotaxin/CCR3 binding interactions exhibit a marked sensitivity to relatively small changes in the extracellular environment. In particular, modest variations in the pH and the level of sodium chloride over a range of physiologic and near physiologic conditions had dramatic effects on eotaxin binding and CCR3-mediated cytoplasmic Ca2+ mobilization. These biochemical indices were reflected at the functional level as well; small changes in pH and salt also resulted in striking changes in the migration of primary human eosinophils in vitro. These results reveal that relatively small perturbations in extracellular buffer conditions can yield widely disparate interpretations of CCR3 ligand binding and affinities and suggest that modulation of the tissue microenvironment might be utilized to control the affinity and efficacy of chemokine-mediated cell migration.

TECK: a novel CC chemokine specifically expressed by thymic dendritic cells and potentially involved in T cell development

A novel CC chemokine was identified in the thymus of mouse and human and was designated TECK (thymus-expressed chemokine). TECK has weak homology to other CC chemokines and maps to mouse chromosome 8. Besides the thymus, mRNA encoding TECK was detected at substantial levels in the small intestine and at low levels in the liver. The source of TECK in the thymus was determined to be thymic dendritic cells; in contrast, bone marrow-derived dendritic cells do not express TECK. The murine TECK recombinant protein showed chemotactic activity for activated macrophages, dendritic cells, and thymocytes. We conclude that TECK represents a novel thymic dendritic cell-specific CC chemokine that is possibly involved in T cell development.

A dendritic-cell-derived C-C chemokine that preferentially attracts naive T cells

Dendritic cells form a system of highly efficient antigen-presenting cells. After capturing antigen in the periphery, they migrate to lymphoid organs where they present the antigen to T cells. Their seemingly unique ability to interact with and sensitize naive T cells gives dendritic cells a central role in the initiation of immune responses and allows them to be used in therapeutic strategies against cancer, viral infection and other diseases. How they interact preferentially with naive rather than activated T lymphocytes is still poorly understood. Chemokines direct the transport of white blood cells in immune surveillance. Here we report the identification and characterization of a C-C chemokine (DC-CK1) that is specifically expressed by human dendritic cells at high levels. Tissue distribution analysis demonstrates that dendritic cells present in germinal centres and T-cell areas of secondary lymphoid organs express this chemokine. We show that DC-CK1, in contrast to RANTES, MIP-1alpha and interleukin-8, preferentially attracts naive T cells (CD45RA+). The specific expression of DC-CK1 by dendritic cells at the site of initiation of an immune response, combined with its chemotactic activity for naive T cells, suggests that DC-CK1 has an important rule in the induction of immune responses.

RANTES stimulation of T lymphocyte adhesion and activation: role for LFA-1 and ICAM-3

The chemokine RANTES is a potent chemoattractant and activator of T lymphocytes. Mechanisms underlying the RANTES-induced activation of T lymphocytes leading to adhesion and migration have not been fully analyzed. We investigate here the function of RANTES in the regulation of T cell adhesion, specifically the induction of homotypic aggregation. RANTES induced the expression of many important cell surface adhesion and activation receptors in a normal human T cell clone and peripheral blood T lymphocytes, including members of the beta 1 and beta 2 integrin family, CD44, CD50, and CD28. Up-regulation of these markers correlated with RANTES-stimulated homotypic adhesion of T cells. This homotypic aggregation event was RANTES dose-dependent, prolonged, and pertussis toxin-independent, but herbimycin A-sensitive, suggesting that it involves signaling through alternative (G alpha i protein-independent) pathways. Using specific monoclonal antibodies, the homotypic aggregation event was shown to be lymphocyte function-associated antigen-1 (LFA-1)-dependent, with no observable interaction through alpha 4 or beta 1 integrins. Intercellular adhesion molecule-3 (ICAM-3) and possibly ICAM-1 participate as LFA-1 ligands. Additionally, RANTES phosphorylated the beta chain of LFA-1 1-2 min following stimulation. These results imply a specific role for the chemokine RANTES in T cell activation and intercellular adhesion.

A new class of membrane-bound chemokine with a CX3C motif

Chemokines direct the trafficking of white blood cells in immune surveillance, playing a key role in inflammatory and infectious diseases such as AIDS. All chemokines studied so far are secreted proteins of relative molecular mass approximately 7K-15K and fall into three families that are defined by a cysteine signature motif: CXC, CC and C (refs 3, 6, 7), where C is a cysteine and X any amino-acid residue. We report here the identification and characterization of a fourth human chemokine type, derived from non-haemopoietic cells and bearing a new CX3C fingerprint. Unlike other chemokine types, the polypeptide chain of the human CX3C chemokine is predicted to be part of a 373-amino-acid protein that carries the chemokine domain on top of an extended mucin-like stalk. This molecule can exist in two forms: either membrane-anchored or as a shed 95K glycoprotein. The soluble CX3C chemokine has potent chemoattractant activity for T cells and monocytes, and the cell-surface-bound protein, which is induced on activated primary endothelial cells, promotes strong adhesion of those leukocytes. The structure, biochemical features, tissue distribution and chromosomal localization of CX3C chemokine all indicate that it represents a unique class of chemokine that may constitute part of the molecular control of leukocyte traffic at the endothelium.

Reconstitution of T cell receptor signaling in ZAP-70-deficient cells by retroviral transduction of the ZAP-70 gene

A variant of severe combined immunodeficiency syndrome (SCID) with a selective inability to produce CD8 single positive T cells and a signal transduction defect in peripheral CD4+ cells has recently been shown to be the result of mutations in the ZAP-70 gene. T cell receptor (TCR) signaling requires the association of the ZAP-70 protein tyrosine kinase with the TCR complex. Human T cell leukemia virus type I-transformed CD4+ T cell lines were established from ZAP-70-deficient patients and normal controls. ZAP-70 was expressed and appropriately phosphorylated in normal T cell lines after TCR engagement, but was not detected in T cell lines from ZAP-70-deficient patients. To determine whether signaling could be reconstituted, wild-type ZAP-70 was introduced into deficient cells with a ZAP-70 retroviral vector. High titer producer clones expressing ZAP-70 were generated in the Gibbon ape leukemia virus packaging line PG13. After transduction, ZAP-70 was detected at levels equivalent to those observed in normal cells, and was appropriately phosphorylated on tyrosine after receptor engagement. The kinase activity of ZAP-70 in the reconstituted cells was also appropriately upregulated by receptor aggregation. Moreover, normal and transduced cells, but not ZAP-70-deficient cells, were able to mobilize calcium after receptor ligation, indicating that proximal TCR signaling was reconstituted. These results indicate that this form of SCID may be corrected by gene therapy.

GlyCAM-1, a physiologic ligand for L-selectin, activates beta 2 integrins on naive peripheral lymphocytes

Naive T cells are selectively recruited from the blood into peripheral lymph nodes during lymphocyte recirculation. L-selectin, a lectin-like receptor, mediates the initial attachment of lymphocytes to high endothelial venules (HEV) in lymph nodes. A subsequent step involving the activation of beta 2 integrins has been proposed to facilitate firm adhesion, but the activating signals are poorly understood. We report here that either antibody-mediated cross-linking of L-selectin on human lymphocytes or treatment of the cells with GlyCAM-1, an HEV-derived, secreted ligand for L-selectin, stimulates their binding to ICAM-1 through the beta 2 integrin pathway. Furthermore, GlyCAM-1 causes the rapid expression of a neoepitope on beta 2 integrins associated with a high-avidity state. Naive (CD45RA+), but not memory (CD45R0+) lymphocytes, respond to L-selectin cross-linking or GlyCAM-1 treatment. Thus, the complexing of L-selectin by specific ligands may provide key signals to naive lymphocytes, contributing to their selective recruitment into peripheral lymphoid organs.

RANTES induces tyrosine kinase activity of stably complexed p125FAK and ZAP-70 in human T cells

The chemokine RANTES is a chemoattractant and activating factor for T lymphocytes. Investigation of the signal transduction mechanisms induced by RANTES in T cells revealed tyrosine phosphorylation of multiple protein species with prominent bands at 70-85 and 120-130 kD. Immunoprecipitation and Western analyses revealed that a protein of 125 kD was identical to the focal adhesion kinase (FAK) pp125FAK. RANTES stimulated phosphorylation of FAK as early as 30 seconds and immunoblots using antiphosphotyrosine monoclonal antibodies revealed that there was consistent phosphorylation of a 68-70 kD species in the pp125FAK immunoprecipitates. Immunoblotting and kinase assays showed this to be two separate proteins, the tyrosine kinase zeta-associated protein (ZAP) 70, and the focal adhesion protein paxillin. These results indicate a potentially important role for RANTES in the generation of T cell focal adhesions and subsequent cell activation via a molecular complex containing FAK, ZAP-70, and paxillin.

Biology of chemokine and classical chemoattractant receptors: differential requirements for adhesion-triggering versus chemotactic responses in lymphoid cells

Several chemoattractant receptors can support agonist-induced, integrin-dependent arrest of rolling neutrophils in inflamed venules in vivo, as well as subsequent crawling into tissues. It has been hypothesized that receptors of the Galpha(i)-linked chemoattractant subfamilies, especially receptors for chemokines, may mediate parallel activation-dependent arrest of homing lymphocyte subsets. However, although several chemokines can attract subsets of B or T cells, robust chemoattractant triggering of resting lymphocyte adhesion to vascular ligands has not been observed. To study the biology of individual leukocyte chemoattractant receptors in a defined lymphoid environment, mouse L1/2 pre-B cells and/or human Jurkat T cells were transfected with alpha (IL-8 receptor A) or beta (MIP-1alpha/CC-CKR-1) chemokine receptors, or with the classical chemoattractant C5a (C5aR) or formyl peptide receptors (fPR). All receptors supported robust agonist-dependent alpha4beta1 integrin-mediated adhesion of lymphocytes to VCAM-1. L1/2 cells cotransfected with fPR and beta7 integrin were also induced to bind MAdCAM-1, suggesting common mechanisms coupling chemoattractant receptors to activation of distinct integrins. Adhesion was rapid but transient, with spontaneous reversion to unstimulated levels within 5 min after peak binding. When observed under flow conditions, alpha4beta1-mediated arrest occurred within seconds after initiation of contact and rolling of IL-8RA transfectants on VCAM-1/IL-8 co-coated surface; and arrest reversed spontaneously after a mean of 5 min with a return to rolling behavior. Each of the receptors also conferred agonist-specific chemotaxis; however, whereas strong adhesion required simultaneous occupancy of many receptors with maximal responses above the Kd, chemotaxis in each case was suppressed at high agonist concentrations. The findings indicate that alpha and beta chemokine as well as classical chemoattractant receptors can trigger robust adhesion as well as directed migration of lymphoid cells, but that the requirements for and kinetics of adhesion triggering and chemotaxis are distinct, thus permitting their independent regulation. They suggest that the discordance between proadhesive and chemoattractant responses of circulating lymphocytes to many chemokines may reflect quantitative aspects of receptor expression and/or coupling rather than qualitative differences in receptor signaling.

Chemokines as mediators of allergic inflammation

The selective distribution of reactive leukocytes to foci of inflammation or lymphoid organs is thought to rely on the generation of highly specific 'attractive' forces which can enhance or subvert the physiological trafficking process. It is becoming increasingly apparent that the selective trafficking of leukocytes is governed by both the release of soluble mediators, or chemoattractants, as well as the matrix upon or through which the cells must traverse. A balance exists between endogenous cellular adhesion receptors (as well as extracellular matrix proteins) and other inducible adhesion receptors which can be up-regulated on this 'docking station'. This dynamic environment provides a prominent signal for leukocyte extravasation from the blood or lymph vessel lumenal surface through to the tissue space. This report reviews current thinking on the delicate interplay between a superfamily of chemoattractant cytokines, the chemokines, and the various classes of cellular adhesion molecules. In it we highlight the idea that the balance between basal and inducible regulators of cell adhesion and migration is critical. Should it be disrupted, the signals responsible for induction and maintenance of an inflammatory response and those responsible for its resolution become disregulated, resulting in inflammatory pathology.

Molecular cloning and functional characterization of a novel member of the C-C chemokine family

Chemokines play an important role in immune and inflammatory responses by inducing migration and adhesion of leukocytes. We have isolated a novel chemokine cDNA, designated CCF18, from a cDNA library of an IL-3-dependent murine pro-B cell line, Ba/F3. The cDNA encodes a protein structurally related to the C-C chemokine members. Among this family, C10 shows the highest homology to CCF18, and MIP-1 alpha also has a significant homology but to a lesser extent. CCF18 produced from COS cells induced chemotaxis and Ca2+ flux in CD4+ T cell clones. Moreover, prior administration of MIP-1 alpha desensitized the cells to CCF18. The CCF18 gene (Scya10) was mapped to a middle region of murine chromosome 11, where other genes for several C-C chemokine members are localized. These results clearly indicate that CCF18 is a new member of the C-C chemokine family. Since a high level of CCF18 mRNA is constitutively expressed in macrophage and myeloid cell lines, CCF18 may play a role in inflammatory processes.

Molecular cloning and functional characterization of a novel member of the C-C chemokine family

Chemokines play an important role in immune and inflammatory responses by inducing migration and adhesion of leukocytes. We have isolated a novel chemokine cDNA, designated CCF18, from a cDNA library of an IL-3-dependent murine pro-B cell line, Ba/F3. The cDNA encodes a protein structurally related to the C-C chemokine members. Among this family, C10 shows the highest homology to CCF18, and MIP-1 alpha also has a significant homology but to a lesser extent. CCF18 produced from COS cells induced chemotaxis and Ca2+ flux in CD4+ T cell clones. Moreover, prior administration of MIP-1 alpha desensitized the cells to CCF18. The CCF18 gene (Scya10) was mapped to a middle region of murine chromosome 11, where other genes for several C-C chemokine members are localized. These results clearly indicate that CCF18 is a new member of the C-C chemokine family. Since a high level of CCF18 mRNA is constitutively expressed in macrophage and myeloid cell lines, CCF18 may play a role in inflammatory processes.

Activation of dual T cell signaling pathways by the chemokine RANTES

The chemokine RANTES induced biphasic mobilization of Ca2+ in T cells. The initial peak, a transient increase in cytosolic Ca2+ mediated by a heterotrimeric guanine nucleotide-binding protein (G protein)--coupled pathway, was associated predominantly with chemotaxis. The second peak, Ca2+ release and sustained influx dependent on protein tyrosine kinases, was associated with a spectrum of cellular responses--Ca2+ channel opening, interleukin-2 receptor expression, cytokine release, and T cell proliferation--characteristic of T cell receptor activation. Other chemokines did not produce these responses. Thus, in addition to inducing chemotaxis, RANTES can act as an antigen-independent activator of T cells in vitro.

Molecular cloning and functional expression of a novel CC chemokine receptor cDNA from a human basophilic cell line

We report the cloning and characterization of a novel basophil CC chemokin receptor, K5-5, from the human immature basophilic cell line KU-812. The predicted protein sequence of K5-5 shows only 49% identity to the macrophage inflammatory protein-1 alpha/RANTES receptor (CC CKR-1) and 47% identity to monocyte chemotactic protein-1 receptor (b form), suggesting that this cDNA encodes a novel member of the CC chemokine receptor family. Analysis of K5-5 mRNA expression indicates that it is restricted to leukocyte-rich tissues. In addition, we have shown significant levels of K5-5 mRNA in human basophils, which were up-regulated by treatment with interleukin-5. The CC chemokines, Macrophage inflammatory protein-1 alpha, RANTES, and monocyte chemotactic protein-1 were able to stimulate a Ca(2+)-activated chloride channel in Xenopus laevis oocytes injected with K5-5 cRNA, whereas no signal was detected in response to monocyte chemotactic protein-2, macrophage inflammatory protein-1 beta, or the CXC chemokine, interleukin-8. Taken together, these results indicate for the first time the presence of a CC chemokine receptor on basophils, which functions as a "shared" CC chemokine receptor and may therefore be implicated in the pathogenesis of basophil-mediated allergic diseases.

Molecular cloning and functional characterization of human lymphotactin

We describe the isolation of a cDNA that encodes human lymphotactin (Ltn), a new class of lymphocyte-specific chemokine. Human Ltn shows similarity to some members of the C-C chemokine family but has lost the first and third cysteine residues that are characteristic of the C-C and C-X-C chemokines. Ltn is chemotactic for lymphocytes but not for monocytes, a characteristic that makes it unique among chemokines. In addition, calcium flux desensitization studies indicate that Ltn uses a unique receptor. The human Ltn gene maps to a different chromosome than do the C-C and C-X-C chemokine families. Taken together, these characteristics indicate that Ltn is the first example of a new class of human chemokines with preferential effects on lymphocytes.

Molecular cloning and functional characterization of human lymphotactin

We describe the isolation of a cDNA that encodes human lymphotactin (Ltn), a new class of lymphocyte-specific chemokine. Human Ltn shows similarity to some members of the C-C chemokine family but has lost the first and third cysteine residues that are characteristic of the C-C and C-X-C chemokines. Ltn is chemotactic for lymphocytes but not for monocytes, a characteristic that makes it unique among chemokines. In addition, calcium flux desensitization studies indicate that Ltn uses a unique receptor. The human Ltn gene maps to a different chromosome than do the C-C and C-X-C chemokine families. Taken together, these characteristics indicate that Ltn is the first example of a new class of human chemokines with preferential effects on lymphocytes.

Peptides from the amino-terminus of RANTES cause chemotaxis of human T-lymphocytes

RANTES is a potent chemotactic and activating agent for a variety of leukocytes including T-lymphocytes. To identify the region of the molecule responsible for this activity, we have made overlapping 10 amino acid peptides scanning the protein. A micro-Boyden chamber chemotaxis assay showed the most efficacious peptides came from at the N-terminus. EC50 values of 8 nM (+/- 2.2 nM), 3.7 nM (+/- 2.0 nM) and 3.1 nM (+/- 2.0 nM) were calculated from dose response curves for the peptides (1-10), (3-12), and (5-14). Control peptides from other regions are not active. In THP-1 cells, none of the peptides give a Ca2+ response. The active peptides are shown to be principally chemotactic rather than chemokinetic by a checker board analysis. The results imply that the principal region of RANTES responsible for chemotaxis is located in the amino terminus.

IL-8-induced signal transduction in T lymphocytes involves receptor-mediated activation of phospholipases C and D

We have characterized the IL-8-induced signal transduction processes in T lymphocytes. A basal level of IL-8 receptor expression was shown on mixed PBL, as identified by using phycoerythrin (PE)-coupled IL-8, and this expression was increased following IL-2 stimulation. Scatchard analysis of T cells revealed competitive binding of IL-8 with a Kd of 0.55 nM, with approximately 1200 receptors per cell, on freshly isolated T cells. After 24 h in culture following purification, reverse transcriptase PCR (RT-PCR) analyses show the mRNA for only the type B IL-8R on these cultured T lymphocytes and the cell line MOLT-4. Stimulation of T lymphocytes or T cell clones with IL-8 led to generation of inositol trisphosphate and calcium flux. In addition, when T cells were prelabeled with [3H]oleic acid, IL-8 caused a long lasting, time- and dose-related increase in [3H]phosphatidylethanol (PtE), indicating activation of phospholipase D (PLD). By contrast, this IL-8-dependent PLD activity was undetectable in IL-8-stimulated neutrophils. PLD activation appeared to be downstream of protein kinase C, because several inhibitors abrogated the increase in [3H]PtE, whereas guanosine-5'-O-(3-thiotriphosphate (GTP(gamma)S) and inositol trisphosphorothioate (IP3S3) both increased the generation of [3H]PtE. Together, these results demonstrate that the IL-8RB receptor is sufficient to mediate phospholipase C (PLC) and PLD activation in T lymphocytes, but not in neutrophils, and indicate an important difference in receptor usage and signal transduction pathways between IL-8-stimulated lymphocytes and neutrophils.

IL-8-induced signal transduction in T lymphocytes involves receptor-mediated activation of phospholipases C and D

We have characterized the IL-8-induced signal transduction processes in T lymphocytes. A basal level of IL-8 receptor expression was shown on mixed PBL, as identified by using phycoerythrin (PE)-coupled IL-8, and this expression was increased following IL-2 stimulation. Scatchard analysis of T cells revealed competitive binding of IL-8 with a Kd of 0.55 nM, with approximately 1200 receptors per cell, on freshly isolated T cells. After 24 h in culture following purification, reverse transcriptase PCR (RT-PCR) analyses show the mRNA for only the type B IL-8R on these cultured T lymphocytes and the cell line MOLT-4. Stimulation of T lymphocytes or T cell clones with IL-8 led to generation of inositol trisphosphate and calcium flux. In addition, when T cells were prelabeled with [3H]oleic acid, IL-8 caused a long lasting, time- and dose-related increase in [3H]phosphatidylethanol (PtE), indicating activation of phospholipase D (PLD). By contrast, this IL-8-dependent PLD activity was undetectable in IL-8-stimulated neutrophils. PLD activation appeared to be downstream of protein kinase C, because several inhibitors abrogated the increase in [3H]PtE, whereas guanosine-5'-O-(3-thiotriphosphate (GTP(gamma)S) and inositol trisphosphorothioate (IP3S3) both increased the generation of [3H]PtE. Together, these results demonstrate that the IL-8RB receptor is sufficient to mediate phospholipase C (PLC) and PLD activation in T lymphocytes, but not in neutrophils, and indicate an important difference in receptor usage and signal transduction pathways between IL-8-stimulated lymphocytes and neutrophils.

Mutation of Leu25 and Val27 introduces CC chemokine activity into interleukin-8

Interleukin-8 (IL-8) is a member of the CXC branch of the chemokine superfamily and activates neutrophils but not monocytes. The related CC chemokine branch, which includes monocyte chemoattractant protein-1 (MCP-1) and RANTES are potent chemoattractants for monocytes but not neutrophils. Examination of the sequences of the CXC chemokines reveals that the highly conserved leucine, corresponding to Leu25 in IL-8, is always replaced by tyrosine in CC chemokines. There is also a high degree of conservation among the CXC chemokines of the adjacent Val27 residue, which points out from the same side of the beta-sheet as Leu25. In RANTES, Val27 is also replaced by a tyrosine. In order to investigate the role of these residues in controlling cell specificity, we have made the single mutants Leu25-->Tyr, Val27-->Tyr and the double mutant Leu25-->Tyr, Val27--> Tyr of IL-8. These proteins have been expressed in Escherichia coli and purified to homogeneity from inclusion body material. All three mutants have lower potency and efficacy in chemotaxis and calcium mobilization assays using neutrophils. The mutants also show lowered affinity to both IL-8 receptors A and B expressed recombinantly in HL-60 cells and to neutrophils in [125I]IL-8 competition assays. Additionally, the Leu25-->Tyr mutation introduces a novel monocyte chemoattractant activity into IL-8. We therefore studied the displacement of [125I]MIP-1 alpha by IL-8 Leu25-->Tyr from the CC-CKR-1 receptor. The mutant displaces MIP-1 alpha ligand with an affinity only 12-fold less than MIP-1 alpha itself. This suggests that mutations in this region of IL-8 are involved in receptor binding and activation and in the control of specificity between CC and CXC chemokines.

A fluorescent interleukin-8 receptor probe produced by targetted labelling at the amino terminus

Interleukin-8 is the most extensively characterised member of the structurally related chemotactic and pro-inflammatory proteins collectively called chemokines. It binds to two closely related members of the seven transmembrane chemokine receptor family found on a variety of leukocyte cell types. In order to study the interaction of interleukin-8 with its receptors, and their distribution, we have produced a fluorescently labelled protein as an alternative to the radioactive 125I-interleukin-8 ligand. Interleukin-8 is naturally produced as two forms, a 72-residue polypeptide by monocytes and a 77-residue form produced by endothelial cells which has an extension of five amino acids at the amino terminal. Both forms are active at nanomolar concentrations, implying that chemical modification to the amino terminus of the 72-residue form will not destroy activity. The 72-residue interleukin-8 sequence starts with a serine residue, which can be oxidised under mild conditions to give a reactive glyoxylyl function which is then reacted with a nucleophilic fluorescein derivative. The site-specifically labelled protein was easily isolated by reverse-phase HPLC. The dissociation constant of the fluorescently labelled interleukin-8 from its receptors on neutrophils was measured by displacement of 125I-interleukin-8 and found to be 10 nM compared to 1 nM for the unmodified protein. The modified protein is highly active in in vitro bioassays using human neutrophils, giving an EC50 of 7 nM in chemotaxis and an EC50 of 0.62 nM for shape change. The binding of the fluorescent protein to neutrophils can also be measured by fluorescent automatic cell sorter (FACS) analysis, and can be competed by unlabelled interleukin-8. The amino-terminal modification of interleukin-8 has produced a reagent which is useful for the quantification of interleukin-8 receptor expression, and will also be useful in monitoring the fate of the ligand after receptor binding.