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CCR11 Is a Functional Receptor for the Monocyte Chemoattractant Protein Family of Chemokines

2000; Elsevier BV; Volume: 275; Issue: 13 Linguagem: Inglês

10.1074/jbc.275.13.9550

1083-351X

Vicki L. Schweickart, Angela Epp, Carol J. Raport, Patrick W. Gray,

T-cell and B-cell Immunology

Chemokines mediate their diverse activities through G protein-coupled receptors. The human homolog of the bovine orphan receptor PPR1 shares significant similarity to chemokine receptors. Transfection of this receptor into murine L1.2 cells resulted in responsiveness to monocyte chemoattractant protein (MCP)-4, MCP-2, and MCP-1 in chemotaxis assays. Binding studies with radiolabeled MCP-4 demonstrated a single high affinity binding site with an IC50 of 0.14 nm. As shown by competition binding, other members of the MCP family also recognized this receptor. MCP-2 was the next most potent ligand, with an IC50 of 0.45 nm. Surprisingly, eotaxin (IC50 = 6.7 nm) and MCP-3 (IC50 = 4.1 nm) bind with greater affinity than MCP-1 (IC50 = 10.7 nm) but only act as agonists in chemotaxis assays at 100-fold higher concentrations. Because of high affinity binding and functional chemotactic responses, we have termed this receptor CCR11. The gene for CCR11 was localized to human chromosome 3q22, which is distinct from most CC chemokine receptor genes at 3p21. Northern blot hybridization was used to identify CCR11 expression in heart, small intestine, and lung. Thus CCR11 shares functional similarity to CCR2 because it recognizes members of the MCP family, but CCR11 has a distinct expression pattern. Chemokines mediate their diverse activities through G protein-coupled receptors. The human homolog of the bovine orphan receptor PPR1 shares significant similarity to chemokine receptors. Transfection of this receptor into murine L1.2 cells resulted in responsiveness to monocyte chemoattractant protein (MCP)-4, MCP-2, and MCP-1 in chemotaxis assays. Binding studies with radiolabeled MCP-4 demonstrated a single high affinity binding site with an IC50 of 0.14 nm. As shown by competition binding, other members of the MCP family also recognized this receptor. MCP-2 was the next most potent ligand, with an IC50 of 0.45 nm. Surprisingly, eotaxin (IC50 = 6.7 nm) and MCP-3 (IC50 = 4.1 nm) bind with greater affinity than MCP-1 (IC50 = 10.7 nm) but only act as agonists in chemotaxis assays at 100-fold higher concentrations. Because of high affinity binding and functional chemotactic responses, we have termed this receptor CCR11. The gene for CCR11 was localized to human chromosome 3q22, which is distinct from most CC chemokine receptor genes at 3p21. Northern blot hybridization was used to identify CCR11 expression in heart, small intestine, and lung. Thus CCR11 shares functional similarity to CCR2 because it recognizes members of the MCP family, but CCR11 has a distinct expression pattern. G protein-coupled receptor(s) base pairs CC chemokine receptor EBI1-ligand chemokine epithelial cell-derived neutrophil-activating protein expressed sequence tag liver and activation-regulated chemokine leukotactin-1 monocyte chemoattractant protein macrophage-derived chemokine macrophage inflammatory protein neutrophil-activating protein-2 pulmonary and activation-regulated chemokine monokine induced by interferon γ interleukin-8, IP-10, interferon γ-inducible protein-10, MGSA, melanocyte growth-stimulating activity platelet factor-4 regulated on activation, normal T cell expressed and secreted stromal cell-derived factor secondary lymphoid tissue chemokine thymus and activation-regulated chemokine thymus-expressed chemokine hemofiltrate CC chemokine Chemokines are a family of small proteins, usually 70–90 amino acids in length, that are responsible for the directed migration of specific cell types (for reviews, see Refs. 1.Baggiolini M. Dewald B. Moser B. Annu. Rev. Immunol. 1997; 15: 675-705Crossref PubMed Scopus (1976) Google Scholar, 2.Luster A.D. N. Engl. J. Med. 1998; 338: 436-445Crossref PubMed Scopus (3233) Google Scholar, 3.Zlotnik A. Morales J. Hedrick J.A. Crit. Rev. Immunol. 1999; 19: 1-47Crossref PubMed Google Scholar, 4.Locati M. Murphy P.M. Annu. Rev. Medicine. 1999; 50: 425-440Crossref PubMed Scopus (252) Google Scholar, 5.Rollins B.J. Blood. 1997; 90: 909-928Crossref PubMed Google Scholar, 6.Schall T.J. Bacon K.B. Curr. Opin. Immunol. 1994; 6: 865-873Crossref PubMed Scopus (608) Google Scholar). The complexity and functions of the chemokine family, now with more than 30 genes, have become increasingly diverse as more members have been identified and characterized. Chemokines play a critical role in the host response to infection because they are responsible for recruitment of leukocyte subsets to sites of pathogen entry (7.Gerard C. Nature. 1998; 395: 217-219Crossref PubMed Scopus (28) Google Scholar, 8.Baggiolini M. Nature. 1998; 392: 565-568Crossref PubMed Scopus (2385) Google Scholar). Many inflammatory diseases, such as rheumatoid arthritis, inflammatory bowel disease, and asthma (9.Wells T.N. Proudfoot A.E. Inflamm. Res. 1999; 48: 353-362Crossref PubMed Scopus (37) Google Scholar), have been associated with elevated chemokine expression. In addition, chemokines are also responsible for the migration of cells within certain lymphoid organs that are critical for leukocyte development, such as thymus (10.Suzuki G. Sawa H. Kobayashi Y. Nakata Y. Nakagawa K. Uzawa A. Sakiyama H. Kakinuma S. Iwabuchi K. Nagashima K. J. Immunol. 1999; 162: 5981-5985PubMed Google Scholar, 11.Campbell J.J. Pan J. Butcher E.C. J. Immunol. 1999; 163: 2353-2357PubMed Google Scholar, 12.Chantry D. Romagnani P. Raport C.J. Wood C.L. Epp A. Romagnani S. Gray P.W. Blood. 1999; 94: 1890-1898Crossref PubMed Google Scholar), lymph node (13.Tang H.L. Cyster J.G. Science. 1999; 284: 819-822Crossref PubMed Scopus (261) Google Scholar), and spleen (14.Pevzner V. Wolf I. Burgstahler R. Forster R. Lipp M. Curr. Top. Microbiol. Immunol. 1999; 246: 79-84Crossref PubMed Scopus (21) Google Scholar,15.Jung S. Littman D.R. Curr. Opin. Immunol. 1999; 11: 319-325Crossref PubMed Scopus (51) Google Scholar). As shown by gene targeting studies, the chemokine stromal cell-derived factor (SDF)-1 is critical for proper neuronal and cardiac development (16.Zou Y.R. Kottmann A.H. Kuroda M. Taniuchi I. Littman D.R. Nature. 1998; 393: 595-599Crossref PubMed Scopus (2107) Google Scholar, 17.Nagasawa T. Hirota S. Tachibana K. Takakura N. Nishikawa S. Kitamura Y. Yoshida N. Kikutani H. Kishimoto T. Nature. 1996; 382: 635-638Crossref PubMed Scopus (1994) Google Scholar). Chemokines have also been implicated in cardiovascular processes such as angiogenesis and atherosclerosis (18.Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar).Chemokines are recognized by specific seven transmembrane-spanning, G protein-coupled receptors (GPCRs)1 (for review, see Refs. 19.Premack B.A. Schall T.J. Nat. Med. 1996; 2: 1174-1178Crossref PubMed Scopus (572) Google Scholar and 20.Berger E.A. Murphy P.M. Farber J.M. Annu. Rev. Immunol. 1999; 17: 657-700Crossref PubMed Scopus (1876) Google Scholar). Previously characterized chemokine receptors share significant homology, with 25–65% identical amino acids, and consequently form their own branch of the GPCR family tree. Many chemokine receptors were originally identified as orphan GPCRs. There remain several orphan GPCRs with high similarity to the chemokine receptor family.The orphan receptor PPR1 was originally isolated from bovine papillary tissue in a search for gustatory receptors (21.Matsuoka I. Mori T. Aoki J. Sato T. Kurihara K. Biochem. Biophys. Res. Commun. 1993; 194: 504-511Crossref PubMed Scopus (40) Google Scholar). However, the expression of PPR1 appears to be higher in lung than in tongue. In addition, PPR1 shares more similarity to chemokine receptors than gustatory or olfactory receptors. Because of this similarity, we isolated a human homolog of PPR1 and examined its ability to function as a chemokine receptor. The human homolog binds members of the MCP family (MCP-1, MCP-2, MCP-3, MCP-4, and eotaxin) with high affinity and also mediates responses to MCP-4, MCP-2, and MCP-1 in chemotaxis assays. In accordance with the Chemokine Nomenclature Committee, we have designated this receptor CCR11.DISCUSSIONCCR11 was identified during a search of the human EST data base for homologs of the bovine orphan PPR1. When the full coding region of CCR11 was assembled, it was found to be 86% identical to PPR1 at the amino acid level. Homology comparisons indicated that CCR11 is most closely related to chemokine receptors. Its closest relatives are CCR7 (36% identical), CCR6 (33%), and CCR9 (33%). Chromosomal mapping of CCR11 localized it to 3q22. Interestingly, many other CC chemokine receptors also map to chromosome 3, including CCR1, CCR2, CCR3, CCR4, CCR5, and CCR8 (26.Samson M. Soularue P. Vassart G. Parmentier M. Genomics. 1996; 36: 522-526Crossref PubMed Scopus (92) Google Scholar). CCR11, however, is significantly separated from these receptors, which are clustered at 3p21–24. This suggests that CCR11 is more distantly related to most CC chemokine receptors, consistent with the sequence homology comparisons presented in Fig. 2. The CCR11 gene maps somewhat closer to the orphan receptor GPR15 (27; also known as BOB, 28) which is located at 3q11.2–13.1 (27.Heiber M. Marchese A. Nguyen T. Heng H.H. George S.R. O'Dowd B.F. Genomics. 1996; 32: 462-465Crossref PubMed Scopus (41) Google Scholar).As demonstrated in binding and chemotaxis studies, CCR11 is a chemokine receptor that recognizes ligands in the MCP family. The primary ligands for CCR11 are MCP-4 and MCP-2, based on binding affinities and agonist properties in chemotaxis experiments. Other MCP family members also interact with CCR11 with lower affinities. Although CCR11 is most closely related to CCR7, it does not interact with the CCR7 ligands ELC and SLC.The MCPs share high homology with each other (56–72%) and form their own branch of the CC chemokine family tree. In addition, the MCPs share some functional similarity and are all closely linked on human chromosome 17q11.2 (29.Nomiyama H. Fukuda S. Iio M. Tanase S. Miura R. Yoshie O. J. Interferon Cytokine Res. 1999; 19: 227-234Crossref PubMed Scopus (34) Google Scholar). However, MCP expression patterns are distinct, with MCP-4 being expressed constitutively in lung, small intestine, and colon (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar), whereas MCP-1 is expressed primarily in cells stimulated with proinflammatory agents (32.Baggiolini M. Dewald B. Moser B. Adv. Immunol. 1994; 55: 97-179Crossref PubMed Scopus (2258) Google Scholar, 33.Godiska R. Chantry D. Raport C.J. Sozzani S. Allavena P. Leviten D. Mantovani A. Gray P.W. J. Exp. Med. 1997; 185: 1595-1604Crossref PubMed Scopus (415) Google Scholar). MCP-4 has been identified previously as an agonist for CCR2 and CCR3 (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar). MCP-2 is recognized by CCR1, CCR2, CCR3, and CCR5 (34.Gong X. Gong W. Kuhns D.B. Ben-Baruch A. Howard O.M.Z. Wang J.M. J. Biol. Chem. 1997; 272: 11682-11685Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar, 35.Heath H. Qin S. Rao P. Wu L. LaRosa G. Kassam N. Ponath P.D. Mackay C.R. J. Clin. Invest. 1997; 99: 178-184Crossref PubMed Scopus (435) Google Scholar, 36.Gong W. Howard O.M.Z. Turpin J.A. Grimm M.C. Ueda H. Gray P.W. Raport C.J. Oppenheim J.J. Wang J.M. J. Biol. Chem. 1998; 273: 4289-4292Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar). MCP-1 is the strongest ligand for the receptor CCR2 (37.Charo I.F. Myers S.J. Herman A. Franci C. Connolly A.J. Coughlin S.R. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 2752-2756Crossref PubMed Scopus (640) Google Scholar), and this receptor also recognizes MCP-2 (34.Gong X. Gong W. Kuhns D.B. Ben-Baruch A. Howard O.M.Z. Wang J.M. J. Biol. Chem. 1997; 272: 11682-11685Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar), MCP-3 (38.Combadiere C. Ahuja S.K. Van Damme J. Tiffany H.L. Gao J.L. Murphy P.M. J. Biol. Chem. 1995; 270: 29671-29675Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar), and MCP-4 (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar). The characterization of MCP family members as ligands for CCR11 adds additional complexity and redundancy to this diverse repertoire of chemokine functions.Identification of ligands for orphan GPCRs can be complex. GPCRs can exhibit paradoxical behavior, particularly transfected recombinant receptors. Although not well understood, such unusual behavior may be caused by inappropriate G protein usage, overexpression of recombinant receptors, or other as yet unidentified phenomena. Our laboratory has noted that some chemokine receptors may not be expressed in a stable manner and that functional responses can be lost if not selected for repeatedly. 2C. J. Raport and P. W. Gray, unpublished observations.Overexpression is a natural consequence of using a strong promoter and may lead to functional responses that are potentially deleterious to transfected cells. Some changes we have observed with GPCR transfectants are increases in cell adhesiveness or decrease in growth rate. 3V. L. Schweickart, B. Steiner, and P. W. Gray, unpublished observations. With CCR11 our transfected cell population was initially selected by chemotaxis. When these cells were cloned, the majority had lost their responsiveness to MCP-4, but some clones responded even more vigorously than the original selected population. Thus, chemotactic selection greatly aided our identification and characterization of CCR11.Compared with other characterized chemokine receptors, we observed only weak calcium mobilization in response to MCP-4 stimulation. Perhaps CCR11 signal transduction is linked to G proteins that are not well complemented in L1.2 cells. Perhaps this receptor does not naturally induce a strong calcium response, like some other GPCRs. Alternatively, CCR11 calcium responses in L1.2 cells may be linked to cellular toxicity. Finally, CCR11 may recognize other, as yet unidentified, ligands that cause more significant calcium flux. Nevertheless, MCP-4 is a major ligand for CCR11 as shown by its strong binding affinity and potent agonist activity in chemotaxis experiments.As shown by Northern blot analysis, CCR11 has an unusual pattern of expression for a chemokine receptor. Because it is not highly expressed in lymphoid organs such as thymus or spleen, CCR11 is not likely to be involved in lymphocyte development as are CCR4, CCR7, and CCR9 (Refs.10.Suzuki G. Sawa H. Kobayashi Y. Nakata Y. Nakagawa K. Uzawa A. Sakiyama H. Kakinuma S. Iwabuchi K. Nagashima K. J. Immunol. 1999; 162: 5981-5985PubMed Google Scholar, 11.Campbell J.J. Pan J. Butcher E.C. J. Immunol. 1999; 163: 2353-2357PubMed Google Scholar, 12.Chantry D. Romagnani P. Raport C.J. Wood C.L. Epp A. Romagnani S. Gray P.W. Blood. 1999; 94: 1890-1898Crossref PubMed Google Scholar, 13.Tang H.L. Cyster J.G. Science. 1999; 284: 819-822Crossref PubMed Scopus (261) Google Scholar, 14.Pevzner V. Wolf I. Burgstahler R. Forster R. Lipp M. Curr. Top. Microbiol. Immunol. 1999; 246: 79-84Crossref PubMed Scopus (21) Google Scholar, 15.Jung S. Littman D.R. Curr. Opin. Immunol. 1999; 11: 319-325Crossref PubMed Scopus (51) Google Scholar). In addition, CCR11 is virtually undetectable in peripheral blood, being primarily expressed in the heart, small intestine, and lung. With the exception of CXCR4, which is broadly expressed in many tissues, chemokine receptors are typically expressed exclusively on cells of lymphoid or myeloid origin. Our inability to detect transcript in these cells may indicate that CCR11 is expressed on a subpopulation of lymphoid cells that are rare in whole blood but resident in specific tissues. CCR3, for example, is expressed only on eosinophils and a subset of Th2 cells and is undetectable by Northern blot in peripheral blood (39.Ponath P.D. Qin S. Post T.W. Wang J. Wu L. Gerard N.P. Newman W. Gerard C. Mackay C.R. J. Exp. Med. 1996; 183: 2437-2448Crossref PubMed Scopus (552) Google Scholar, 40.Sallusto F. Mackay C.R. Lanzavecchia A. Science. 1997; 277: 2005-2007Crossref PubMed Scopus (930) Google Scholar). Alternatively, CCR11 may be expressed on parenchymal cells and play a role currently unappreciated for chemokine receptors. Although chemokines and chemokine receptors are generally known for their role in immune cell development and trafficking, there is preliminary evidence that they may have functions outside of the immune system. Knockout experiments have shown that CXCR4 is essential for normal development of the heart, small intestine and brain (16.Zou Y.R. Kottmann A.H. Kuroda M. Taniuchi I. Littman D.R. Nature. 1998; 393: 595-599Crossref PubMed Scopus (2107) Google Scholar, 41.Tachibana K. Hirota S. Iizasa H. Yoshida H. Kawabata K. Kataoka Y. Kitamura Y. Matsushima K. Yoshida N. Nishikawa S. Kishimoto T. Nagasawa T. Nature. 1998; 393: 591-594Crossref PubMed Scopus (1313) Google Scholar). In addition, Streblow et al. (43.Streblow D.N. Soderberg-Naucler C. Vieira J. Smith P. Wakabayashi E. Ruchti F. Mattison K. Altschuler Y. Nelson J.A. Cell. 1999; 99: 511-520Abstract Full Text Full Text PDF PubMed Scopus (350) Google Scholar) have recently proposed that the virally encoded chemokine receptor US28 may play a role in the migration of smooth muscle cells seen in cytomegalovirus exacerbation of vascular disease (43.Streblow D.N. Soderberg-Naucler C. Vieira J. Smith P. Wakabayashi E. Ruchti F. Mattison K. Altschuler Y. Nelson J.A. Cell. 1999; 99: 511-520Abstract Full Text Full Text PDF PubMed Scopus (350) Google Scholar).Based on its expression pattern, CCR11 may function in cells that are resident in highly vascularized tissues. MCP-1 and CCR2 have previously been associated with atherogenesis and are thought to play a role in recruitment of macrophages to initiate atherosclerotic plaque formation (18.Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar, 44.Boring L. Gosling J. Cleary M. Charo I.F. Nature. 1998; 394: 894-897Crossref PubMed Scopus (1668) Google Scholar). Vascular expression of MCP family members results in CCR2-mediated monocyte recruitment and macrophage development; this may be accompanied by CCR11-mediated events. Perhaps CCR2 and CCR11 complement each other in vascular processes such as remodeling of the vessel wall to accommodate monocyte influx. The complex redundancy of MCP chemokines and their receptors in the vasculature may help to explain the results of transgenic and gene knockout studies (18.Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar, 42.Gu L. Okada Y. Clinton S.K. Gerard C. Sukhova G.K. Libby P. Rollins B.J. Mol. Cell. 1998; 2: 275-281Abstract Full Text Full Text PDF PubMed Scopus (1359) Google Scholar,44.Boring L. Gosling J. Cleary M. Charo I.F. Nature. 1998; 394: 894-897Crossref PubMed Scopus (1668) Google Scholar, 45.Grewal I.S. Rutledge B.J. Fiorillo J.A. Gu L. Gladue R.P. Flavell R.A. Rollins B.J. J. Immunol. 1997; 159: 401-408PubMed Google Scholar). These gene alterations are not lethal and often do not have severe complications on their own, suggesting a compensatory role of genes with similar function. Further studies with CCR11 and its ligands will be required to understand fully their roles in health and disease. Chemokines are a family of small proteins, usually 70–90 amino acids in length, that are responsible for the directed migration of specific cell types (for reviews, see Refs. 1.Baggiolini M. Dewald B. Moser B. Annu. Rev. Immunol. 1997; 15: 675-705Crossref PubMed Scopus (1976) Google Scholar, 2.Luster A.D. N. Engl. J. Med. 1998; 338: 436-445Crossref PubMed Scopus (3233) Google Scholar, 3.Zlotnik A. Morales J. Hedrick J.A. Crit. Rev. Immunol. 1999; 19: 1-47Crossref PubMed Google Scholar, 4.Locati M. Murphy P.M. Annu. Rev. Medicine. 1999; 50: 425-440Crossref PubMed Scopus (252) Google Scholar, 5.Rollins B.J. Blood. 1997; 90: 909-928Crossref PubMed Google Scholar, 6.Schall T.J. Bacon K.B. Curr. Opin. Immunol. 1994; 6: 865-873Crossref PubMed Scopus (608) Google Scholar). The complexity and functions of the chemokine family, now with more than 30 genes, have become increasingly diverse as more members have been identified and characterized. Chemokines play a critical role in the host response to infection because they are responsible for recruitment of leukocyte subsets to sites of pathogen entry (7.Gerard C. Nature. 1998; 395: 217-219Crossref PubMed Scopus (28) Google Scholar, 8.Baggiolini M. Nature. 1998; 392: 565-568Crossref PubMed Scopus (2385) Google Scholar). Many inflammatory diseases, such as rheumatoid arthritis, inflammatory bowel disease, and asthma (9.Wells T.N. Proudfoot A.E. Inflamm. Res. 1999; 48: 353-362Crossref PubMed Scopus (37) Google Scholar), have been associated with elevated chemokine expression. In addition, chemokines are also responsible for the migration of cells within certain lymphoid organs that are critical for leukocyte development, such as thymus (10.Suzuki G. Sawa H. Kobayashi Y. Nakata Y. Nakagawa K. Uzawa A. Sakiyama H. Kakinuma S. Iwabuchi K. Nagashima K. J. Immunol. 1999; 162: 5981-5985PubMed Google Scholar, 11.Campbell J.J. Pan J. Butcher E.C. J. Immunol. 1999; 163: 2353-2357PubMed Google Scholar, 12.Chantry D. Romagnani P. Raport C.J. Wood C.L. Epp A. Romagnani S. Gray P.W. Blood. 1999; 94: 1890-1898Crossref PubMed Google Scholar), lymph node (13.Tang H.L. Cyster J.G. Science. 1999; 284: 819-822Crossref PubMed Scopus (261) Google Scholar), and spleen (14.Pevzner V. Wolf I. Burgstahler R. Forster R. Lipp M. Curr. Top. Microbiol. Immunol. 1999; 246: 79-84Crossref PubMed Scopus (21) Google Scholar,15.Jung S. Littman D.R. Curr. Opin. Immunol. 1999; 11: 319-325Crossref PubMed Scopus (51) Google Scholar). As shown by gene targeting studies, the chemokine stromal cell-derived factor (SDF)-1 is critical for proper neuronal and cardiac development (16.Zou Y.R. Kottmann A.H. Kuroda M. Taniuchi I. Littman D.R. Nature. 1998; 393: 595-599Crossref PubMed Scopus (2107) Google Scholar, 17.Nagasawa T. Hirota S. Tachibana K. Takakura N. Nishikawa S. Kitamura Y. Yoshida N. Kikutani H. Kishimoto T. Nature. 1996; 382: 635-638Crossref PubMed Scopus (1994) Google Scholar). Chemokines have also been implicated in cardiovascular processes such as angiogenesis and atherosclerosis (18.Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar). Chemokines are recognized by specific seven transmembrane-spanning, G protein-coupled receptors (GPCRs)1 (for review, see Refs. 19.Premack B.A. Schall T.J. Nat. Med. 1996; 2: 1174-1178Crossref PubMed Scopus (572) Google Scholar and 20.Berger E.A. Murphy P.M. Farber J.M. Annu. Rev. Immunol. 1999; 17: 657-700Crossref PubMed Scopus (1876) Google Scholar). Previously characterized chemokine receptors share significant homology, with 25–65% identical amino acids, and consequently form their own branch of the GPCR family tree. Many chemokine receptors were originally identified as orphan GPCRs. There remain several orphan GPCRs with high similarity to the chemokine receptor family. The orphan receptor PPR1 was originally isolated from bovine papillary tissue in a search for gustatory receptors (21.Matsuoka I. Mori T. Aoki J. Sato T. Kurihara K. Biochem. Biophys. Res. Commun. 1993; 194: 504-511Crossref PubMed Scopus (40) Google Scholar). However, the expression of PPR1 appears to be higher in lung than in tongue. In addition, PPR1 shares more similarity to chemokine receptors than gustatory or olfactory receptors. Because of this similarity, we isolated a human homolog of PPR1 and examined its ability to function as a chemokine receptor. The human homolog binds members of the MCP family (MCP-1, MCP-2, MCP-3, MCP-4, and eotaxin) with high affinity and also mediates responses to MCP-4, MCP-2, and MCP-1 in chemotaxis assays. In accordance with the Chemokine Nomenclature Committee, we have designated this receptor CCR11. DISCUSSIONCCR11 was identified during a search of the human EST data base for homologs of the bovine orphan PPR1. When the full coding region of CCR11 was assembled, it was found to be 86% identical to PPR1 at the amino acid level. Homology comparisons indicated that CCR11 is most closely related to chemokine receptors. Its closest relatives are CCR7 (36% identical), CCR6 (33%), and CCR9 (33%). Chromosomal mapping of CCR11 localized it to 3q22. Interestingly, many other CC chemokine receptors also map to chromosome 3, including CCR1, CCR2, CCR3, CCR4, CCR5, and CCR8 (26.Samson M. Soularue P. Vassart G. Parmentier M. Genomics. 1996; 36: 522-526Crossref PubMed Scopus (92) Google Scholar). CCR11, however, is significantly separated from these receptors, which are clustered at 3p21–24. This suggests that CCR11 is more distantly related to most CC chemokine receptors, consistent with the sequence homology comparisons presented in Fig. 2. The CCR11 gene maps somewhat closer to the orphan receptor GPR15 (27; also known as BOB, 28) which is located at 3q11.2–13.1 (27.Heiber M. Marchese A. Nguyen T. Heng H.H. George S.R. O'Dowd B.F. Genomics. 1996; 32: 462-465Crossref PubMed Scopus (41) Google Scholar).As demonstrated in binding and chemotaxis studies, CCR11 is a chemokine receptor that recognizes ligands in the MCP family. The primary ligands for CCR11 are MCP-4 and MCP-2, based on binding affinities and agonist properties in chemotaxis experiments. Other MCP family members also interact with CCR11 with lower affinities. Although CCR11 is most closely related to CCR7, it does not interact with the CCR7 ligands ELC and SLC.The MCPs share high homology with each other (56–72%) and form their own branch of the CC chemokine family tree. In addition, the MCPs share some functional similarity and are all closely linked on human chromosome 17q11.2 (29.Nomiyama H. Fukuda S. Iio M. Tanase S. Miura R. Yoshie O. J. Interferon Cytokine Res. 1999; 19: 227-234Crossref PubMed Scopus (34) Google Scholar). However, MCP expression patterns are distinct, with MCP-4 being expressed constitutively in lung, small intestine, and colon (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar), whereas MCP-1 is expressed primarily in cells stimulated with proinflammatory agents (32.Baggiolini M. Dewald B. Moser B. Adv. Immunol. 1994; 55: 97-179Crossref PubMed Scopus (2258) Google Scholar, 33.Godiska R. Chantry D. Raport C.J. Sozzani S. Allavena P. Leviten D. Mantovani A. Gray P.W. J. Exp. Med. 1997; 185: 1595-1604Crossref PubMed Scopus (415) Google Scholar). MCP-4 has been identified previously as an agonist for CCR2 and CCR3 (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar). MCP-2 is recognized by CCR1, CCR2, CCR3, and CCR5 (34.Gong X. Gong W. Kuhns D.B. Ben-Baruch A. Howard O.M.Z. Wang J.M. J. Biol. Chem. 1997; 272: 11682-11685Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar, 35.Heath H. Qin S. Rao P. Wu L. LaRosa G. Kassam N. Ponath P.D. Mackay C.R. J. Clin. Invest. 1997; 99: 178-184Crossref PubMed Scopus (435) Google Scholar, 36.Gong W. Howard O.M.Z. Turpin J.A. Grimm M.C. Ueda H. Gray P.W. Raport C.J. Oppenheim J.J. Wang J.M. J. Biol. Chem. 1998; 273: 4289-4292Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar). MCP-1 is the strongest ligand for the receptor CCR2 (37.Charo I.F. Myers S.J. Herman A. Franci C. Connolly A.J. Coughlin S.R. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 2752-2756Crossref PubMed Scopus (640) Google Scholar), and this receptor also recognizes MCP-2 (34.Gong X. Gong W. Kuhns D.B. Ben-Baruch A. Howard O.M.Z. Wang J.M. J. Biol. Chem. 1997; 272: 11682-11685Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar), MCP-3 (38.Combadiere C. Ahuja S.K. Van Damme J. Tiffany H.L. Gao J.L. Murphy P.M. J. Biol. Chem. 1995; 270: 29671-29675Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar), and MCP-4 (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar). The characterization of MCP family members as ligands for CCR11 adds additional complexity and redundancy to this diverse repertoire of chemokine functions.Identification of ligands for orphan GPCRs can be complex. GPCRs can exhibit paradoxical behavior, particularly transfected recombinant receptors. Although not well understood, such unusual behavior may be caused by inappropriate G protein usage, overexpression of recombinant receptors, or other as yet unidentified phenomena. Our laboratory has noted that some chemokine receptors may not be expressed in a stable manner and that functional responses can be lost if not selected for repeatedly. 2C. J. Raport and P. W. Gray, unpublished observations.Overexpression is a natural consequence of using a strong promoter and may lead to functional responses that are potentially deleterious to transfected cells. Some changes we have observed with GPCR transfectants are increases in cell adhesiveness or decrease in growth rate. 3V. L. Schweickart, B. Steiner, and P. W. Gray, unpublished observations. With CCR11 our transfected cell population was initially selected by chemotaxis. When these cells were cloned, the majority had lost their responsiveness to MCP-4, but some clones responded even more vigorously than the original selected population. Thus, chemotactic selection greatly aided our identification and characterization of CCR11.Compared with other characterized chemokine receptors, we observed only weak calcium mobilization in response to MCP-4 stimulation. Perhaps CCR11 signal transduction is linked to G proteins that are not well complemented in L1.2 cells. Perhaps this receptor does not naturally induce a strong calcium response, like some other GPCRs. Alternatively, CCR11 calcium responses in L1.2 cells may be linked to cellular toxicity. Finally, CCR11 may recognize other, as yet unidentified, ligands that cause more significant calcium flux. Nevertheless, MCP-4 is a major ligand for CCR11 as shown by its strong binding affinity and potent agonist activity in chemotaxis experiments.As shown by Northern blot analysis, CCR11 has an unusual pattern of expression for a chemokine receptor. Because it is not highly expressed in lymphoid organs such as thymus or spleen, CCR11 is not likely to be involved in lymphocyte development as are CCR4, CCR7, and CCR9 (Refs.10.Suzuki G. Sawa H. Kobayashi Y. Nakata Y. Nakagawa K. Uzawa A. Sakiyama H. Kakinuma S. Iwabuchi K. Nagashima K. J. Immunol. 1999; 162: 5981-5985PubMed Google Scholar, 11.Campbell J.J. Pan J. Butcher E.C. J. Immunol. 1999; 163: 2353-2357PubMed Google Scholar, 12.Chantry D. Romagnani P. Raport C.J. Wood C.L. Epp A. Romagnani S. Gray P.W. Blood. 1999; 94: 1890-1898Crossref PubMed Google Scholar, 13.Tang H.L. Cyster J.G. Science. 1999; 284: 819-822Crossref PubMed Scopus (261) Google Scholar, 14.Pevzner V. Wolf I. Burgstahler R. Forster R. Lipp M. Curr. Top. Microbiol. Immunol. 1999; 246: 79-84Crossref PubMed Scopus (21) Google Scholar, 15.Jung S. Littman D.R. Curr. Opin. Immunol. 1999; 11: 319-325Crossref PubMed Scopus (51) Google Scholar). In addition, CCR11 is virtually undetectable in peripheral blood, being primarily expressed in the heart, small intestine, and lung. With the exception of CXCR4, which is broadly expressed in many tissues, chemokine receptors are typically expressed exclusively on cells of lymphoid or myeloid origin. Our inability to detect transcript in these cells may indicate that CCR11 is expressed on a subpopulation of lymphoid cells that are rare in whole blood but resident in specific tissues. CCR3, for example, is expressed only on eosinophils and a subset of Th2 cells and is undetectable by Northern blot in peripheral blood (39.Ponath P.D. Qin S. Post T.W. Wang J. Wu L. Gerard N.P. Newman W. Gerard C. Mackay C.R. J. Exp. Med. 1996; 183: 2437-2448Crossref PubMed Scopus (552) Google Scholar, 40.Sallusto F. Mackay C.R. Lanzavecchia A. Science. 1997; 277: 2005-2007Crossref PubMed Scopus (930) Google Scholar). Alternatively, CCR11 may be expressed on parenchymal cells and play a role currently unappreciated for chemokine receptors. Although chemokines and chemokine receptors are generally known for their role in immune cell development and trafficking, there is preliminary evidence that they may have functions outside of the immune system. Knockout experiments have shown that CXCR4 is essential for normal development of the heart, small intestine and brain (16.Zou Y.R. Kottmann A.H. Kuroda M. Taniuchi I. Littman D.R. Nature. 1998; 393: 595-599Crossref PubMed Scopus (2107) Google Scholar, 41.Tachibana K. Hirota S. Iizasa H. Yoshida H. Kawabata K. Kataoka Y. Kitamura Y. Matsushima K. Yoshida N. Nishikawa S. Kishimoto T. Nagasawa T. Nature. 1998; 393: 591-594Crossref PubMed Scopus (1313) Google Scholar). In addition, Streblow et al. (43.Streblow D.N. Soderberg-Naucler C. Vieira J. Smith P. Wakabayashi E. Ruchti F. Mattison K. Altschuler Y. Nelson J.A. Cell. 1999; 99: 511-520Abstract Full Text Full Text PDF PubMed Scopus (350) Google Scholar) have recently proposed that the virally encoded chemokine receptor US28 may play a role in the migration of smooth muscle cells seen in cytomegalovirus exacerbation of vascular disease (43.Streblow D.N. Soderberg-Naucler C. Vieira J. Smith P. Wakabayashi E. Ruchti F. Mattison K. Altschuler Y. Nelson J.A. Cell. 1999; 99: 511-520Abstract Full Text Full Text PDF PubMed Scopus (350) Google Scholar).Based on its expression pattern, CCR11 may function in cells that are resident in highly vascularized tissues. MCP-1 and CCR2 have previously been associated with atherogenesis and are thought to play a role in recruitment of macrophages to initiate atherosclerotic plaque formation (18.Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar, 44.Boring L. Gosling J. Cleary M. Charo I.F. Nature. 1998; 394: 894-897Crossref PubMed Scopus (1668) Google Scholar). Vascular expression of MCP family members results in CCR2-mediated monocyte recruitment and macrophage development; this may be accompanied by CCR11-mediated events. Perhaps CCR2 and CCR11 complement each other in vascular processes such as remodeling of the vessel wall to accommodate monocyte influx. The complex redundancy of MCP chemokines and their receptors in the vasculature may help to explain the results of transgenic and gene knockout studies (18.Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar, 42.Gu L. Okada Y. Clinton S.K. Gerard C. Sukhova G.K. Libby P. Rollins B.J. Mol. Cell. 1998; 2: 275-281Abstract Full Text Full Text PDF PubMed Scopus (1359) Google Scholar,44.Boring L. Gosling J. Cleary M. Charo I.F. Nature. 1998; 394: 894-897Crossref PubMed Scopus (1668) Google Scholar, 45.Grewal I.S. Rutledge B.J. Fiorillo J.A. Gu L. Gladue R.P. Flavell R.A. Rollins B.J. J. Immunol. 1997; 159: 401-408PubMed Google Scholar). These gene alterations are not lethal and often do not have severe complications on their own, suggesting a compensatory role of genes with similar function. Further studies with CCR11 and its ligands will be required to understand fully their roles in health and disease. CCR11 was identified during a search of the human EST data base for homologs of the bovine orphan PPR1. When the full coding region of CCR11 was assembled, it was found to be 86% identical to PPR1 at the amino acid level. Homology comparisons indicated that CCR11 is most closely related to chemokine receptors. Its closest relatives are CCR7 (36% identical), CCR6 (33%), and CCR9 (33%). Chromosomal mapping of CCR11 localized it to 3q22. Interestingly, many other CC chemokine receptors also map to chromosome 3, including CCR1, CCR2, CCR3, CCR4, CCR5, and CCR8 (26.Samson M. Soularue P. Vassart G. Parmentier M. Genomics. 1996; 36: 522-526Crossref PubMed Scopus (92) Google Scholar). CCR11, however, is significantly separated from these receptors, which are clustered at 3p21–24. This suggests that CCR11 is more distantly related to most CC chemokine receptors, consistent with the sequence homology comparisons presented in Fig. 2. The CCR11 gene maps somewhat closer to the orphan receptor GPR15 (27; also known as BOB, 28) which is located at 3q11.2–13.1 (27.Heiber M. Marchese A. Nguyen T. Heng H.H. George S.R. O'Dowd B.F. Genomics. 1996; 32: 462-465Crossref PubMed Scopus (41) Google Scholar). As demonstrated in binding and chemotaxis studies, CCR11 is a chemokine receptor that recognizes ligands in the MCP family. The primary ligands for CCR11 are MCP-4 and MCP-2, based on binding affinities and agonist properties in chemotaxis experiments. Other MCP family members also interact with CCR11 with lower affinities. Although CCR11 is most closely related to CCR7, it does not interact with the CCR7 ligands ELC and SLC. The MCPs share high homology with each other (56–72%) and form their own branch of the CC chemokine family tree. In addition, the MCPs share some functional similarity and are all closely linked on human chromosome 17q11.2 (29.Nomiyama H. Fukuda S. Iio M. Tanase S. Miura R. Yoshie O. J. Interferon Cytokine Res. 1999; 19: 227-234Crossref PubMed Scopus (34) Google Scholar). However, MCP expression patterns are distinct, with MCP-4 being expressed constitutively in lung, small intestine, and colon (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar), whereas MCP-1 is expressed primarily in cells stimulated with proinflammatory agents (32.Baggiolini M. Dewald B. Moser B. Adv. Immunol. 1994; 55: 97-179Crossref PubMed Scopus (2258) Google Scholar, 33.Godiska R. Chantry D. Raport C.J. Sozzani S. Allavena P. Leviten D. Mantovani A. Gray P.W. J. Exp. Med. 1997; 185: 1595-1604Crossref PubMed Scopus (415) Google Scholar). MCP-4 has been identified previously as an agonist for CCR2 and CCR3 (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar). MCP-2 is recognized by CCR1, CCR2, CCR3, and CCR5 (34.Gong X. Gong W. Kuhns D.B. Ben-Baruch A. Howard O.M.Z. Wang J.M. J. Biol. Chem. 1997; 272: 11682-11685Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar, 35.Heath H. Qin S. Rao P. Wu L. LaRosa G. Kassam N. Ponath P.D. Mackay C.R. J. Clin. Invest. 1997; 99: 178-184Crossref PubMed Scopus (435) Google Scholar, 36.Gong W. Howard O.M.Z. Turpin J.A. Grimm M.C. Ueda H. Gray P.W. Raport C.J. Oppenheim J.J. Wang J.M. J. Biol. Chem. 1998; 273: 4289-4292Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar). MCP-1 is the strongest ligand for the receptor CCR2 (37.Charo I.F. Myers S.J. Herman A. Franci C. Connolly A.J. Coughlin S.R. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 2752-2756Crossref PubMed Scopus (640) Google Scholar), and this receptor also recognizes MCP-2 (34.Gong X. Gong W. Kuhns D.B. Ben-Baruch A. Howard O.M.Z. Wang J.M. J. Biol. Chem. 1997; 272: 11682-11685Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar), MCP-3 (38.Combadiere C. Ahuja S.K. Van Damme J. Tiffany H.L. Gao J.L. Murphy P.M. J. Biol. Chem. 1995; 270: 29671-29675Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar), and MCP-4 (30.Garcia-Zepeda E.A. Combadiere C. Rothenberg M.E. Sarafi M.N. Lavigne F. Hamid Q. Murphy P.M. Luster A.D. J. Immunol. 1996; 157: 5613-5626PubMed Google Scholar, 31.Godiska R. Chantry D. Raport C.J. Schweickart V.L. Trong H.L. Gray P.W. J. Leukocyte Biol. 1997; 61: 353-360Crossref PubMed Scopus (31) Google Scholar). The characterization of MCP family members as ligands for CCR11 adds additional complexity and redundancy to this diverse repertoire of chemokine functions. Identification of ligands for orphan GPCRs can be complex. GPCRs can exhibit paradoxical behavior, particularly transfected recombinant receptors. Although not well understood, such unusual behavior may be caused by inappropriate G protein usage, overexpression of recombinant receptors, or other as yet unidentified phenomena. Our laboratory has noted that some chemokine receptors may not be expressed in a stable manner and that functional responses can be lost if not selected for repeatedly. 2C. J. Raport and P. W. Gray, unpublished observations.Overexpression is a natural consequence of using a strong promoter and may lead to functional responses that are potentially deleterious to transfected cells. Some changes we have observed with GPCR transfectants are increases in cell adhesiveness or decrease in growth rate. 3V. L. Schweickart, B. Steiner, and P. W. Gray, unpublished observations. With CCR11 our transfected cell population was initially selected by chemotaxis. When these cells were cloned, the majority had lost their responsiveness to MCP-4, but some clones responded even more vigorously than the original selected population. Thus, chemotactic selection greatly aided our identification and characterization of CCR11. Compared with other characterized chemokine receptors, we observed only weak calcium mobilization in response to MCP-4 stimulation. Perhaps CCR11 signal transduction is linked to G proteins that are not well complemented in L1.2 cells. Perhaps this receptor does not naturally induce a strong calcium response, like some other GPCRs. Alternatively, CCR11 calcium responses in L1.2 cells may be linked to cellular toxicity. Finally, CCR11 may recognize other, as yet unidentified, ligands that cause more significant calcium flux. Nevertheless, MCP-4 is a major ligand for CCR11 as shown by its strong binding affinity and potent agonist activity in chemotaxis experiments. As shown by Northern blot analysis, CCR11 has an unusual pattern of expression for a chemokine receptor. Because it is not highly expressed in lymphoid organs such as thymus or spleen, CCR11 is not likely to be involved in lymphocyte development as are CCR4, CCR7, and CCR9 (Refs.10.Suzuki G. Sawa H. Kobayashi Y. Nakata Y. Nakagawa K. Uzawa A. Sakiyama H. Kakinuma S. Iwabuchi K. Nagashima K. J. Immunol. 1999; 162: 5981-5985PubMed Google Scholar, 11.Campbell J.J. Pan J. Butcher E.C. J. Immunol. 1999; 163: 2353-2357PubMed Google Scholar, 12.Chantry D. Romagnani P. Raport C.J. Wood C.L. Epp A. Romagnani S. Gray P.W. Blood. 1999; 94: 1890-1898Crossref PubMed Google Scholar, 13.Tang H.L. Cyster J.G. Science. 1999; 284: 819-822Crossref PubMed Scopus (261) Google Scholar, 14.Pevzner V. Wolf I. Burgstahler R. Forster R. Lipp M. Curr. Top. Microbiol. Immunol. 1999; 246: 79-84Crossref PubMed Scopus (21) Google Scholar, 15.Jung S. Littman D.R. Curr. Opin. Immunol. 1999; 11: 319-325Crossref PubMed Scopus (51) Google Scholar). In addition, CCR11 is virtually undetectable in peripheral blood, being primarily expressed in the heart, small intestine, and lung. With the exception of CXCR4, which is broadly expressed in many tissues, chemokine receptors are typically expressed exclusively on cells of lymphoid or myeloid origin. Our inability to detect transcript in these cells may indicate that CCR11 is expressed on a subpopulation of lymphoid cells that are rare in whole blood but resident in specific tissues. CCR3, for example, is expressed only on eosinophils and a subset of Th2 cells and is undetectable by Northern blot in peripheral blood (39.Ponath P.D. Qin S. Post T.W. Wang J. Wu L. Gerard N.P. Newman W. Gerard C. Mackay C.R. J. Exp. Med. 1996; 183: 2437-2448Crossref PubMed Scopus (552) Google Scholar, 40.Sallusto F. Mackay C.R. Lanzavecchia A. Science. 1997; 277: 2005-2007Crossref PubMed Scopus (930) Google Scholar). Alternatively, CCR11 may be expressed on parenchymal cells and play a role currently unappreciated for chemokine receptors. Although chemokines and chemokine receptors are generally known for their role in immune cell development and trafficking, there is preliminary evidence that they may have functions outside of the immune system. Knockout experiments have shown that CXCR4 is essential for normal development of the heart, small intestine and brain (16.Zou Y.R. Kottmann A.H. Kuroda M. Taniuchi I. Littman D.R. Nature. 1998; 393: 595-599Crossref PubMed Scopus (2107) Google Scholar, 41.Tachibana K. Hirota S. Iizasa H. Yoshida H. Kawabata K. Kataoka Y. Kitamura Y. Matsushima K. Yoshida N. Nishikawa S. Kishimoto T. Nagasawa T. Nature. 1998; 393: 591-594Crossref PubMed Scopus (1313) Google Scholar). In addition, Streblow et al. (43.Streblow D.N. Soderberg-Naucler C. Vieira J. Smith P. Wakabayashi E. Ruchti F. Mattison K. Altschuler Y. Nelson J.A. Cell. 1999; 99: 511-520Abstract Full Text Full Text PDF PubMed Scopus (350) Google Scholar) have recently proposed that the virally encoded chemokine receptor US28 may play a role in the migration of smooth muscle cells seen in cytomegalovirus exacerbation of vascular disease (43.Streblow D.N. Soderberg-Naucler C. Vieira J. Smith P. Wakabayashi E. Ruchti F. Mattison K. Altschuler Y. Nelson J.A. Cell. 1999; 99: 511-520Abstract Full Text Full Text PDF PubMed Scopus (350) Google Scholar). Based on its expression pattern, CCR11 may function in cells that are resident in highly vascularized tissues. MCP-1 and CCR2 have previously been associated with atherogenesis and are thought to play a role in recruitment of macrophages to initiate atherosclerotic plaque formation (18.Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar, 44.Boring L. Gosling J. Cleary M. Charo I.F. Nature. 1998; 394: 894-897Crossref PubMed Scopus (1668) Google Scholar). Vascular expression of MCP family members results in CCR2-mediated monocyte recruitment and macrophage development; this may be accompanied by CCR11-mediated events. Perhaps CCR2 and CCR11 complement each other in vascular processes such as remodeling of the vessel wall to accommodate monocyte influx. The complex redundancy of MCP chemokines and their receptors in the vasculature may help to explain the results of transgenic and gene knockout studies (18.Gosling J. Slaymaker S. Gu L. Tseng S. Zlot C.H. Young S.G. Rollins B.J. Charo I.F. J. Clin. Invest. 1999; 103: 773-778Crossref PubMed Scopus (594) Google Scholar, 42.Gu L. Okada Y. Clinton S.K. Gerard C. Sukhova G.K. Libby P. Rollins B.J. Mol. Cell. 1998; 2: 275-281Abstract Full Text Full Text PDF PubMed Scopus (1359) Google Scholar,44.Boring L. Gosling J. Cleary M. Charo I.F. Nature. 1998; 394: 894-897Crossref PubMed Scopus (1668) Google Scholar, 45.Grewal I.S. Rutledge B.J. Fiorillo J.A. Gu L. Gladue R.P. Flavell R.A. Rollins B.J. J. Immunol. 1997; 159: 401-408PubMed Google Scholar). These gene alterations are not lethal and often do not have severe complications on their own, suggesting a compensatory role of genes with similar function. Further studies with CCR11 and its ligands will be required to understand fully their roles in health and disease. The L1.2 cell line was kindly provided by the laboratory of Dr. Irv Weissman (Stanford Medical School, Stanford CA). We thank Dina Leviten, Marsalina Quiggle, and Aaron Smith for DNA sequencing and oligonucleotide synthesis and Dan Allison and Jennifer Running Deer for the pNEF6 vector. Drs. David Chantry and Mark Hill provided valuable comments on the manuscript. We also thank Drs. Craig Gerard, Phil Murphy, and Tom Schall for advice with the CCR11 nomenclature.