MOLECULAR-CLONING OF A NOVEL HUMAN CC CHEMOKINE EBI1-LIGAND CHEMOKINETHAT IS A SPECIFIC FUNCTIONAL LIGAND FOR EBI1, CCR7

By searching the expressed sequence tag (EST) data base, we identified partial cDNA sequences encoding a novel human CC chemokine. We determ ined the complete cDNA sequence that encodes a highly basic polypeptid e of a total 98 amino acids with 20 to 30% identity to other human CC chemokines. We termed this novel chemokine from EBI1-Ligand Chemokine as ELC (see below). The ELC mRNA was most strongly expressed in the th ymus and lymph nodes. Recombinant ELC protein was expressed as a fusio n protein with the Flag tag (ELC-Flag). For receptor-binding assays, r ecombinant ELC protein fused with the secreted form of alkaline phosph atase (SEAP) was used. By stably expressing five CC chemokine receptor s (CCR1 to 5) and five orphan receptors, ELC-SEAP was found to bind sp ecifically to an orphan receptor EBI1. Only ELC-Flag, but not MCP-1, M CP-2, MCP-3, eotaxin, MIP-1 alpha, MIP-1 beta, RANTES (regulated on ac tivation normal T cell expressed and secreted), thymus and activation- regulated chemokine (TARC), or liver and activation-regulated chemokin e (LARC), competed with ELC-SEAP for EBI1. ELC-Flag-induced transient calcium mobilization and chemotactic responses in EBI1-transfected cel ls. ELC-Flag also induced chemotaxis in HUT78 cells expressing endogen ous EBI1 at high levels. By somatic hybrid and radiation hybrid analys es, the gene for ELC (SCYA19) was mapped to chromosome 9p13 instead of chromosome 17q11.2 where the genes for CC chemokines are clustered. T aken together, ELC is a highly specific ligand for EBI1, which is know n to be expressed in activated B and T lymphocytes and strongly up-reg ulated in B cells infected with Epstein-Barr virus and T cells infecte d with herpesvirus 6 or 7. ELC and EBI1 may thus play roles in migrati on and homing of normal lymphocytes, as well. as in pathophysiology of lymphocytes infected with these herpesviruses. We propose EBI1 to be designated as CCR7.