CCR3

CCR3 Charles R. Mackay* The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst (Sydney), New South Wales, 2010, Australia * corresponding author tel: 61-2-92958405, fax: 61-2-92958404, e-mail: [email protected] DOI: 10.1006/rwcy.2000.22003.

SUMMARY CCR3 is a chemokine receptor, closely related to CCR1, CCR2, and CCR5. CCR3 is the principal chemokine receptor on eosinophils that mediates their migration to a variety of chemokines, including eotaxin, eotaxin 2, RANTES, MCP-2, MCP-3, and MCP-4. CCR3 is also expressed by other allergic leukocytes such as basophils, mast cells, and TH2 cells. Blocking CCR3 or CCR3 ligands has proven to be effective in animal models of asthma, for reducing inflammation and bronchohyperreactivity. For these reasons CCR3 is one of the promising targets for drug development for allergic disease.

BACKGROUND

Discovery The discovery of CCR3 arose from studies aimed at characterizing the chemokines and chemokine receptors for eosinophil migration. Eosinophils are selectively recruited into certain inflammatory lesions as a result of IgE-mediated reactions, for instance in rhinitis and allergic asthma, and also in response to certain parasitic infections (Kay and Corrigan, 1992; Gleich et al., 1993). This suggested the presence of a chemoattractant receptor on eosinophils that was expressed in a relatively restricted fashion, distinct from other receptors such as the C5a receptor which is also expressed on neutrophils. The chemokine eotaxin, first identified in guinea pigs (Jose et al., 1994) and subsequently in humans (Ponath et al., 1996a) and mouse (Gonzalo et al., 1996), is unusual in that it is selectively chemotactic for eosinophils. Binding studies with 125I-labeled eotaxin and peripheral blood eosinophils showed that eotaxin bound

a receptor on eosinophils distinct from CCR1 or CCR2, as specific binding could not compete with MIP-1 or MCP-1 (Ponath et al., 1996a). In addition, receptor cross-desensitization experiments using eosinophils suggested that at least one additional receptor existed that signals in response to RANTES and MCP-3 (Baggiolini and Dahinden, 1994; Dahinden et al., 1994), but not MIP-1. Based on the structure of other chemokine receptors, novel seven transmembrane receptors were sought that were expressed in eosinophils, and bound eotaxin. In humans, CCR3 was identified as an eosinophilic chemokine receptor that principally bound eotaxin and with lower affinity RANTES and MCP-3 (Daugherty et al., 1996; Ponath et al., 1996b). In mice, CCR3 was reported as a MIP-1 receptor (Post et al., 1995), although murine CCR3 has subsequently been shown also to bind murine eotaxin with high affinity. A difference between mouse and human CCR3 is the ability of mouse CCR3 to bind MIP-1.

Alternative names The accepted nomenclature for this receptor is CCR3, although in the early papers this receptor was referred to as CCR-3, CKR-3, and CC CKR-3. This receptor is sometimes referred to as the eotaxin receptor since eotaxin binds with high affinity and fidelity to this receptor. Nevertheless, this is a misnomer since numerous chemokines bind CCR3.

Structure CCR3 exhibits the seven transmembrane, G proteincoupled receptor structure typical of all of the

2056 Charles R. Mackay chemokine receptors. It contains the motif DRYLAIVHA in the second intracellular loop, which is common to many members of the chemokine receptor family. CCR3 is somewhat unusual in that it does not contain sites for N-linked glycosylation.

Main activities and pathophysiological roles CCR3 expression on eosinophils, basophils, and TH2 cells is the likely explanation for the selective recruitment of these cells to certain inflammatory sites. Its expression on eosinophils, in particular, may account for the striking accumulation of eosinophils at sites where eotaxin is produced, because eotaxin binds only to CCR3, and eosinophils are much more chemotactic in response to eotaxin than other CCR3bearing cells such as basophils or TH2 cells. CCR3eotaxin interactions may trigger eosinophil arrest during the multistep process of leukocyte binding to endothelium under flow conditions (Kitayama et al., 1998), leading to selective eosinophil recruitment to a tissue. In addition, expression of eotaxin by epithelial cells in allergic airways (Ponath et al., 1996; Ying et al., 1997) might also lead to selective eosinophil migration to certain areas of a tissue. Epithelial cell destruction by eosinophils is one of the pathological hallmarks of allergic asthma. CCR3 has been the target of numerous drug development efforts, for the treatment of allergic disease, particularly asthma. In addition to its role in chemoattraction, CCR3 activation also leads to mediator release by eosinophils and basophils (Uguccioni et al., 1997). The importance of this aspect of CCR3 for allergic inflammation is not known. Although CCR3 is expressed at high levels on basophils, other chemokine receptors appear to be more important for triggering basophil mediator release, particularly CCR2 (Uguccioni et al., 1997). All activities of eotaxin presumably occur through CCR3, and so reports that eotaxin stimulates the growth of myeloid cell progenitors and the differentiation of mast cells during embryonic development (Quackenbush et al., 1997) implicates a role for CCR3 in these processes. CCR3 is also expressed by mature human mast cells in vitro and appears to be one of the principal chemokine receptors for these cells, although CCR3 appears not to function for chemotaxis (Ochi et al., 1999). CCR3 ligands also enhance antigen-stimulated IL-4 production by basophils, which suggests that chemokines such as eotaxin amplify allergic inflammation through effects on cytokine production (Devouassoux et al., 1999).

CCR3 also serves as a coreceptor for certain strains of HIV-1 (Choe et al., 1996), and may be one of the principal receptors in the brain for neurotropic strains of HIV-1 (He et al., 1997). CCR3 can interact with Envs from certain macrophage (M)-tropic strains (which also use CCR5), T cell line-tropic laboratoryadapted strains (which also use CXCR4), and certain dual-tropic primary isolates (which also use CCR2b, CCR5, and CXCR4). CCR3 expression on some cytotoxic T cells enables chemokines such as RANTES to stimulate anti-HIV cytotoxic activity (Hadida et al., 1998). Kaposi's sarcoma-associated herpesvirus (KSHV or HHV-8) encodes chemokinelike proteins, including vMIP-II, which activate and chemoattract human eosinophils by way of CCR3 (Boshoff et al., 1997).

GENE

Accession numbers GenBank: Human: U49727, U51241 Mouse: U29677 Guinea pig: AF060698

Sequence See Figure 1 for human CCR3.

PROTEIN

Accession numbers SwissProt: Human: P51677 Mouse: P51678

Sequence See Figure 2.

Relevant homologies and species differences CCR3 is most closely related to CCR1 (62% amino acid similarity in humans).

CCR3 2057 Figure 1 1 61 121 181 241 301 361 421 481 541 601 661 721 781 841 901 961 1021 1081 1141 1201 1261 1321 1381 1441 1501 1561 1621 1681

AATCCTTTTC GCTATCACAT GGATGATTAT ATGACAACCT GGCCTGCTCT TACTCCCTGG AAATACAGGA CTGCTCTTCC TTTGGCCATG ATCTTTTTCA GCCCTTCGAG GCAGTGCTAG ACTCTTTGCA CTGAGAATGA GGAATCATCA ATTTTTGTCA CTCTCTTCCT CTGGTCATGC TACGCCTTTG CTCATGCACC TCTGTCTCTC AATTGCCTAA CCTCTAAAAC ATACACACAG GGGCAGCGTA TACCTATATT AAACTTTTTA CACAATACAA GAAAAGCTT

Gene sequence for human CCR3.

CTGGCACCTC GTGGCATCTT GCTTCATTGT CACTAGATAC GTGAAAAAGC TGTTCACTGT GGCTCCGAAT TCGTCACCCT GCATGTGTAA TAATCCTGCT CCCGGACTGT CAGCTCTTCC GTGCTCTTTA CCATCTTCTG AAACGCTGCT TCATGGCGGT ATCAATCCAT TGGTGACAGA TTGGAGAGAG TGGGCAGATA CATCCACAGC AGAGGAAGGA AGTCCTTCAA CAGTAGCAGT CTCATCATCA TTAATGCACC TATTTTATAC TAAGTTAACT

TGATATCCTT TGTTGAGTAC GGGATTGTAT AGTTGAGACC TGATACCAGA GGGCCTCTTG TATGACCAAC TCCATTCTGG GCTCCTCTCA GACAATCGAC CACTTTTGGT TGAATTTATC CCCAGAGGAT TCTCGTTCTC GAGGTGCCCC GTTTTTCATT CTTATTTGGA GGTGATCGCC GTTCCGGAAG CATCCCATTC AGAGCCGGAA CCAAGGAGAT ACCTTCCAGT AGATGCATGT ACCTAAAAAG TGAATGTTAG ATTAACTTCA ATTTTATTTT

TTGAAATTCA ATGAATAAAT TTTTCTTCTT TTTGGTACCA GCACTGATGG GGCAATGTGG ATCTACCTGC ATCCACTATG GGGTTTTATC AGGTACCTGG GTCATCACCA TTCTATGAGA ACAGTATATA CCTCTGCTCG AGTAAAAAAA TTCTGGACAC AATGACTGTG TACTCCCACT TACCTGCGCC CTTCCTAGTG CTCTCTATTG NAAGCAAACA GCAACACTGA ACCCTAAGGT CAGAGCTTTG ATAGTTACTA GCCAGCTATT CTAATGTGCC

TGTTAAAGAA CAACTGGTGT CTATCACAGG CATCCTACTA CCCAGTTTGT TGGTGGTGAT TCAACCTGGC TCAGGGGGCA ACACAGGCTT CCATTGTCCA GCATCGTCAC CTGAAGAGTT GCTGGAGGCA TTATGGCCAT AGTACAAGGC CCTACAATGT AGCGGACGAA GCTGCATGAA ACTTCTTCCA AGAAGCTGGA TGTTTTAGGT CATTAAGCCT AGCTCTTAAG CATTACCACA CTTCTCTCTC TATGCCGCTA ATATAAATAA TAGTTCTTTC

TCCCTAGGCT GTTTTACGGA GAGAAGTGAA TGATGACGTG GCCCCCGCTG GATCCTCATA CATTTCGGAC TAACTGGGTT GTACAGCGAG TGCTGTGTTT CTGGGGCCTG GTTTGAAGAG TTTCCACACT CTGCTACACA CATCCGGCTC GGCTATCCTT GCATCTGGAC CCCGGTGATC CAGGCACTTG AAGAACCAGC AGATGCAGAA TCCACACTCA ACACTGAAAT GGCCAGGGCT TAAAATGAGT CAAAAAGGTA AACATTTTCA CCTGCTTAAT

Figure 2 Amino acid sequence for CCR3. MTTSLDTVET GNVVVVMILI FGHGMCKLLS VITSIVTWGL LRMTIFCLVL FWTPYNVAIL YAFVGERFRK

FGTTSYYDDV KYRRLRIMTN GFYHTGLYSE AVLAALPEFI PLLVMAICYT LSSYQSILFG YLRHFFHRHL

GLLCEKADTR IYLLNLAISD IFFIILLTID FYETEELFEE GIIKTLLRCP NDCERTKHLD LMHLGRYIPF

Affinity for ligand(s) The known ligands for CCR3 are listed in Table 1. Of all the ligands, eotaxin has the highest affinity for CCR3, and produces the most potent biological effects on eosinophils.

Cell types and tissues expressing the receptor CCR3 is the main chemokine receptor expressed on eosinophils. It is also expressed on other leukocytes involved in allergic reactions, such as basophils (Uguccioni et al., 1997), mast cells (Ochi et al., 1999),

ALMAQFVPPL LLFLVTLPFW RYLAIVHAVF TLCSALYPED SKKKYKAIRL LVMLVTEVIA LPSEKLERTS

YSLVFTVGLL IHYVRGHNWV ALRARTVTFG TVYSWRHFHT IFVIMAVFFI YSHCCMNPVI SVSPSTAEPE LSIVF

and TH2 cells (Gerber et al., 1997; Sallusto et al., 1997, 1998) (Table 2). As such, it is thought to be important for the development of allergic or antiparasitic reactions. CCR3 was considered at first to be relatively restricted in expression; however, a more detailed analysis of various cells revealed CCR3 expression or upregulation on other cell types (Table 2). For instance, some cells of the monocytemacrophage lineage express CCR3, including microglia (Ghorpade et al., 1998).

Regulation of receptor expression CCR3 is expressed at high levels on eosinophils, and cytokines such as IL-5 do not affect receptor level or functional activity (Heath et al., 1997). CCR3 can be

2058 Charles R. Mackay Table 1 CCR3 ligands and their receptor binding properties Chemokine

Kd (nmol/L)

Other receptors bound

Principal references

Eotaxin

1.5

Ponath et al., 1996b; Heath et al., 1997

Eotaxin 2

ND

Forssmann et al., 1997

RANTES

3.1

CCR1, CCR5

Ponath et al., 1996b; Heath et al., 1997

MCP-2

ND

CCR2, CCR5

Ponath et al., 1996b; Heath et al., 1997

MCP-3

2.7

CCR1, CCR2, CCR5

Ponath et al., 1996b; Heath et al., 1997

MCP-4

ND

CCR2

Garcia-Zepeda et al., 1996; Heath et al., 1997

ND

CCR1

Coulin et al., 1997; Youn et al., 1997

ND

CCR1, CCR5

Post et al., 1995

ND

CCR5

Boshoff et al., 1997

MIP-5/Leukotactin 1 a

MIP-1

vMIP-II

b

a

Mouse chemokine active on mouse CCR3. Human MIP-1 does not bind human CCR3. Chemokine-like protein encoded by Kaposi's sarcoma-associated herpesvirus.

b

Table 2 CCR3 expression pattern Cell type

Eosinophils

Expression

References

Resting

Activated

+++a

+++

Heath et al., 1997

Basophils

+++

+++

Uguccioni et al., 1997

TH2 T cells

+

+/ÿ

Sallusto et al., 1997

Mast cells

+

?

Ochi et al., 1999

Monocyte-macrophages

+

+

Ghorpade et al., 1998

Microglia

++

++

Ghorpade et al., 1998

Neutrophils

ÿ

+

Bonecchi et al., 1999

a

Levels of CCR3 on eosinophils and basophils are approximately 5  104 sites per cell.

expressed on neutrophils after activation by IFN (Bonnechi et al., 1999). CCR3 expression is regulated on TH2 cells, through the influence of cytokines such as IL-2 and IL-4 (Jinquan et al., 1999). Anti-CD3 activation of TH2 cells may lead to CCR3 downregulation, as it does for certain chemokine receptors on other cell types (Sallusto et al., 1999).

SIGNAL TRANSDUCTION

information on CCR3 signaling that distinguishes this receptor from other CC chemokine receptors.

BIOLOGICAL CONSEQUENCES OF ACTIVATING OR INHIBITING RECEPTOR AND PATHOPHYSIOLOGY

Cytoplasmic signaling cascades

Unique biological effects of activating the receptors

CCR3 is a G protein-coupled receptor, and is inhibited by pertussis toxin. There is currently no

CCR3 is principally a chemoattractant receptor, although, like other chemokine receptors, it functions

CCR3 2059 in mediator release from basophils and eosinophils. Expression of CCR3 ligands in tissues is thought to be responsible for the accumulation of allergic leukocytes ± eosinophils, basophils, and TH2 cells, in the tissue.

Phenotypes of receptor knockouts and receptor overexpression mice The phenotype of CCR3 knockout mice has not yet been reported, although these mice have been generated (Gerard, personal communication) and their phenotype should be published in the near future.

THERAPEUTIC UTILITY CCR3 is one of the most actively pursued targets in the pharmaceutical industry for allergic inflammation. The seven transmembrane structure of this receptor lends itself to inhibition by small molecule antagonists. In addition, an mAb, 7B11, has been produced that completely blocks ligand binding and functional activity of CCR3.

Effects of inhibitors (antibodies) to receptors The best characterized antagonist of human CCR3 reported to date is the 7B11 mAb. This mAb is fully antagonistic in functional assays, including transendothelial chemotaxis and calcium release assays (Heath et al., 1997). The responses of eosinophils from most individuals to eotaxin, RANTES, MCP-2, MCP-3, and MCP-4 is mediated entirely through CCR3, since in most individuals this anti-CCR3 mAb is able completely to block eosinophil responses to these chemokines (Heath et al., 1997). At present this mAb is not commercially available, and inquiries should be made directly to Millennium Pharmaceuticals, Cambridge, MA, USA. A potentially useful CCR3 antagonist is Met-Ck 7, which is highly specific and prevents signaling through CCR3 (Nibbs et al., 2000). Proof of principle for CCR3 in vivo has been difficult to establish, since mAbs to rodent CCR3 have been difficult to generate. A complicating factor for proof of principle studies in rodents is that mouse eosinophils also express CCR1, whereas in humans CCR1 expression on eosinophils is variable. However, blocking studies using antibodies to one of the ligands for CCR3, eotaxin, showed that anti-eotaxin

polyclonal antibody was able substantially to reduce allergic inflammation and broncho-hyperreactivity in a mouse airway model (Gonzalo et al., 1998). In addition, eotaxin-deficient mice have reduced eosinophil recruitment to the airways in lung allergic models (Rothenberg et al., 1997). Met-RANTES, which blocks CCR1 and CCR3 (the two main eosinophilic chemokine receptors in the mouse; Elsner et al., 1997), is also able to inhibit airway inflammation and bronchoreactivity in mouse models (Gonzalo et al., 1998). Recently, an mAb to guinea pig CCR3 has been produced that blocks eosinophil migration to eotaxin injected in vivo (Sabroe et al., 1998). Whether this mAb blocks eosinophil migration during an allergic reaction, or broncho-hyperreactivity in the guinea pig asthma model, has yet to be reported. A rat mAb to mouse CCR3 has been produced (Grimaldi et al., 1999), which is nonblocking, although it does deplete eosinophils from the circulation in parasitechallenged mice.

References Baggiolini, M., and Dahinden, C. A. (1994). CC chemokines in allergic inflammation. Immunol. Today 15, 127±133. Bonecchi, R., Polentarutti, N., Luini, W., Borsatti, A., Bernasconi, S., Locati, M., Power, C., Proudfoot, A., Wells, T. N., Mackay, C., Mantovani, A., and Sozzani, S. (1999). Up-regulation of CCR1 and CCR3 and induction of chemotaxis to CC chemokines by IFN-gamma in human neutrophils. J. Immunol. 162, 474±479. Boshoff, C., Endo, Y., Collins, P. D., Takeuchi, Y., Reeves, J. D., Schweickart, V. L., Siani, M. A., Sasaki, T., Williams, T. J., Gray, P. W., Moore, P. S., Chang, Y., and Weiss, R. A. (1997). Angiogenic and HIV-inhibitory functions of KSHVencoded chemokines [see comments]. Science 278, 290±294. Choe, H., Farzan, M., Sun, Y., Sullivan, N., Rollins, B., Ponath, P. D., Wu, L., Mackay, C. R., LaRosa, G., Newman, W., Gerard, N., Gerard, C., and Sodroski, J. (1996). The beta-chemokine receptors CCR3 and CCR5 facilitate infection by primary HIV-1 isolates. Cell 85, 1135±1148. Coulin, F., Power, C. A., Alouani, S., Peitsch, M. C., Schroeder, J. M., Moshizuki, M., Clark-Lewis, I., and Wells, T. N. (1997). Characterisation of macrophage inflammatory protein-5/human CC cytokine-2, a member of the macrophage-inflammatory-protein family of chemokines. Eur. J. Biochem. 248, 507±515. Daugherty, B. L., Siciliano, S. J., DeMartino, J. A., Malkowitz, L., Sirotina, A., and Springer, M. S. (1996). Cloning, expression, and characterization of the human eosinophil eotaxin receptor. J. Exp. Med. 183, 2349±2354. Dahinden, C. A., Geiser, T., Brunner, T., von Tscharner, V., Caput, D., Ferrara, P., Minty, A., and Baggiolini, M. (1994). Monocyte chemotactic protein 3 is a most effective basophiland eosinophil-activating chemokine. J. Exp. Med. 179, 751± 756. Devouassoux, G., Metcalfe, D. D., and Prussin, C. (1999). Eotaxin potentiates antigen-dependent basophil IL-4 production. J. Exp. Med. 190, 267±280.

2060 Charles R. Mackay Elsner, J., Petering, H., Hochstetter, R., Kimmig, D., Wells, T. N., Kapp, A., and Proudfoot, A. E. (1997). The CC chemokine antagonist Met-RANTES inhibits eosinophil effector functions through the chemokine receptors CCR1 and CCR3. Eur. J. Immunol. 27, 2892±2898. Forssmann, U., Uguccioni, M., Loetscher, P., Dahinden, C. A., Langen, H., Thelen, M., and Baggiolini, M. (1997). Eotaxin-2, a novel CC chemokine that is selective for the chemokine receptor CCR3, and acts like eotaxin on human eosinophil and basophil leukocytes. J. Exp. Med. 185, 2171±2176. Garcia-Zepeda, E. A., Combadiere, C., Rothenberg, M. E., Sarafi, M. N., Lavigne, F., Hamid, Q., Murphy, P. M., and Luster, A. D. (1996). Human monocyte chemoattractant protein (MCP)-4 is a novel CC chemokine with activities on monocytes, eosinophils, and basophils induced in allergic and nonallergic inflammation that signals through the CC chemokine receptors (CCR)-2 and -3. J. Immunol. 157, 5613± 5626. Gerber, B. O., Zanni, M. P., Uguccioni, M., Loetscher, M., Mackay, C. R., Pichler, W. J., Yawalkar, N., Baggiolini, M., and Moser, B. (1997). Functional expression of the eotaxin receptor CCR3 in T lymphocytes co-localizing with eosinophils. Curr. Biol. 7, 836±843. Ghorpade, A., Xia, M. Q., Hyman, B. T., Persidsky, Y., Nukuna, A., Bock, P., Che, M., Limoges, J., Gendelman, H. E., and Mackay, C. R. (1998). Role of the beta-chemokine receptors CCR3 and CCR5 in human immunodeficiency virus type 1 infection of monocytes and microglia. J. Virol. 72, 3351±3361. Gleich, G. J., Adolphson, C. R., and Leiferman, K. M. (1993). The biology of the eosinophilic leukocyte. Annu. Rev. Med. 44, 85±101. Gonzalo, J.-A., Jia, G.-Q., Aguirre, V., Friend, D., Coyle, A. J., Jenkins, N. A., Lin, G.-S., Katz, H., Lichtman, A., Copeland, N., Kopf, M., and Gutierrez-Ramos, J.-C. (1996). Mouse eotaxin expression parallels eosinophil accumulation during lung allergic inflammation but is not restricted to a TH2-type response. Immunity 4, 1±14. Gonzalo, J. A., Lloyd, C. M., Wen, D., Albar, J. P., Wells, T. N., Proudfoot, A., Martinez, A. C., Dorf, M., Bjerke, T., Coyle, A. J., and Gutierrez-Ramos, J. C. (1998). The coordinated action of CC chemokines in the lung orchestrates allergic inflammation and airway hyperresponsiveness. J. Exp. Med. 188, 157±167. Grimaldi, J. C., Yu, N. X., Grunig, G., Seymour, B. W., Cottrez, F., Robinson, D. S., Hosken, N., Ferlin, W. G., Wu, X., Soto, H., O'Garra, A., Howard, M. C., and Coffman, R. L. (1999). Depletion of eosinophils in mice through the use of antibodies specific for C-C chemokine receptor 3 (CCR3). J. Leukoc. Biol. 65, 846±853. Hadida, F., Vieillard, V., Autran, B., Clark-Lewis, I., Baggiolini, M., and Debre, P. (1998). HIV-specific T cell cytotoxicity mediated by RANTES via the chemokine receptor CCR3. J. Exp. Med. 188, 609±614. He, J., Chen, Y., Farzan, M., Choe, H., Ohagen, A., Gartner, S., Busciglio, J., Yang, X., Hofmann, W., Newman, W., Mackay, C. R., Sodroski, J., and Gabuzda, D. (1997). CCR3 and CCR5 are co-receptors for HIV-1 infection of microglia. Nature 385, 645±649. Heath, H., Qin, S., Rao, P., Wu, L., LaRosa, G., Kassam, N., Ponath, P. D., and Mackay, C. R. (1997). Chemokine receptor usage by human eosinophils. The importance of CCR3 demonstrated using an antagonistic monoclonal antibody. J. Clin. Invest. 99, 178±184. Jinquan, T., Quan, S., Feili, G., Larsen, C. G., and ThestrupPedersen, K. (1999). Eotaxin activates T cells to chemotaxis

and adhesion only if induced to express CCR3 by IL-2 together with IL-4. J. Immunol. 162, 4285±4292. Jose, P. J., Griffiths-Johnson, D. A., Collins, P. D., Walsh, D. T., Moqbel, R., Totty, N. F., Truong, O., Hsuan, J. J., and Williams, T. J. (1994). Eotaxin: a potent eosinophil chemoattractant cytokine detected in a guinea pig model of allergic airways inflammation. J. Exp. Med. 179, 881±887. Kay, A. B., and Corrigan, C. J. (1992). Asthma. Eosinophils and neutrophils. Br. Med. Bull. 48, 51±64. Kitayama, J., Mackay, C. R., Ponath, P. D., and Springer, T. A. (1998). The C-C chemokine receptor CCR3 participates in stimulation of eosinophil arrest on inflammatory endothelium in shear flow. J. Clin. Invest. 101, 2017±2024. Nibbs, R. J., Salcedo, T. W., Campbell, J. D., Yao, X. T., Li, Y., Nardelli, B., Olsen, H. S., Morris, T. S., Proudfoot, A. E., Patel, V. P., and Graham, G. J. (2000). C-C chemokine receptor 3 antagonism by the beta-chemokine macrophage inflammatory protein 4, a property strongly enhanced by an amino-terminal alanine-methionine swap. J. Immunol. 164, 1488±1497. Ochi, H., Hirani, W. M., Yuan, Q., Friend, D. S., Austen, K. F., and Boyce, J. A. (1999). T helper cell type 2 cytokine-mediated comitogenic responses and CCR3 expression during differentiation of human mast cells in vitro. J. Exp. Med. 190, 267±280. Ponath, P. D., Qin, S., Ringler, D. J., Clark-Lewis, I., Wang, J., Kassam, N., Smith, H., Shi, X., Gonzalo, J. A., Newman, W., Gutierrez-Ramos, J. C., and Mackay, C. R. (1996a). Cloning of the human eosinophil chemoattractant, eotaxin. Expression, receptor binding, and functional properties suggest a mechanism for the selective recruitment of eosinophils. J. Clin. Invest. 97, 604±612. Ponath, P. D., Qin, S., Post, T. W., Wang, J., Wu, L., Gerard, N. P., Newman, W., Gerard, C., and Mackay, C. R. (1996b). Molecular cloning and characterization of a human eotaxin receptor expressed selectively on eosinophils. J. Exp. Med. 183, 2437±2448. Post, T. W., Bozic, C. R., Rothenberg, M. E., Luster, A. D., Gerard, N., and Gerard, C. (1995). Molecular characterization of two murine eosinophil beta chemokine receptors. J. Immunol. 155, 5299±5305. Quackenbush, E. J., Aguirre, V., Wershil, B. K., and GutierrezRamos, J. C. (1997). Eotaxin influences the development of embryonic hematopoietic progenitors in the mouse. J. Leukoc. Biol. 62, 661±666. Quackenbush, E. J., Wershil, B. K., Aguirre, V., and GutierrezRamos, J. C. (1998). Eotaxin modulates myelopoiesis and mast cell development from embryonic hematopoietic progenitors. Blood 92, 1887±1897. Rothenberg, M. E., MacLean, J. A., Pearlman, E., Luster, A. D., and Leder, P. (1997). Targeted disruption of the chemokine eotaxin partially reduces antigen-induced tissue eosinophilia. J. Exp. Med. 185, 785±790. Sabroe, I., Conroy, D. M., Gerard, N. P., Li, Y., Collins, P. D., Post, T. W., Jose, P. J., Williams, T. J., Gerard, C. J., and Ponath, P. D. (1998). Cloning and characterization of the guinea pig eosinophil eotaxin receptor, C-C chemokine receptor-3: blockade using a monoclonal antibody in vivo. J. Immunol. 161, 6139±6147. Sallusto, F., Mackay, C., and Lanzavecchia, A. (1997). Selective expression of the eotaxin receptor CCR3 by human T helper 2 cells. Science 277, 2005±2007. Sallusto, F., Lenig, D., Mackay, C. R., and Lanzavecchia, A. (1998). Flexible programs of chemokine receptor expression on human polarized T helper 1 and 2 lymphocytes. J. Exp. Med. 187, 875±883. Sallusto, F., Kremmer, E., Palermo, B., Hoy, A., Ponath, P., Qin, S., Forster, R., Lipp, M., and Lanzavecchia, A. (1999).

CCR3 2061 Switch in chemokine receptor expression upon TCR stimulation reveals novel homing potential for recently activated T cells. Eur. J. Immunol. 29, 2037±2045. Uguccioni, M., Mackay, C. R., Ochensberger, B., Loetscher, P., Rhis, S., LaRosa, G. J., Rao, P., Ponath, P. D., Baggiolini, M., and Dahinden, C. A. (1997). High expression of the chemokine receptor CCR3 in human blood basophils. Role in activation by eotaxin, MCP-4, and other chemokines. J. Clin. Invest. 100, 1137±1143. Ying, S., Robinson, D., Meng, Q., Rottman, J., Kennedy, R., Ringler, D. J., Mackay, C. R., Daugherty, B. L., Springer, M. S., Durham, S. R., Williams, T. J., and Kay, A. B. (1997). Enhanced expression of eotaxin and CCR3 mRNA and protein in atopic asthma. Association with airway hyperresponsiveness and predominant co-localization of eotaxin mRNA to bronchial epithelial and endothelial cells. Eur. J. Immunol. 27, 3507±3516.

Youn, B. S., Zhang, S. M., Lee, E. K., Park, D. H., Broxmeyer, H. E., Murphy, P. M., Locati, M., Pease, J. E., Kim, K. K., Antol, K., and Kwon, B. S. (1997). Molecular cloning of leukotactin-1: a novel human beta-chemokine, a chemoattractant for neutrophils, monocytes, and lymphocytes, and a potent agonist at CC chemokine receptors 1 and 3. J. Immunol. 159, 5201±5205.

LICENSED PRODUCTS NIH AIDS Research and Reference Reagent Program McKesson Bioservices, Rockville, MD 20850, USA