MOLECULAR-CLONING OF A NOVEL HUMAN CC CHEMOKINE SECONDARY LYMPHOID-TISSUE CHEMOKINE THAT IS A POTENT CHEMOATTRACTANT FOR LYMPHOCYTES AND MAPPED TO CHROMOSOME 9P13

By searching the Expressed Sequence Tag (EST) data base, we identified partial cDNA sequences potentially encoding a novel human CC chemokin e. We determined the entire cDNA sequence which encodes a highly basic polypeptide of 134 amino acids total with a putative signal peptide o f 23 amino acids. The predicted mature protein of 111 amino acids has the four canonical cysteine residues and shows 21-33% identity to othe r human CC chemokines, but has a unique carboxyl-terminal extension of about 30 amino acids which contains two extra cysteine residues. The mRNA was expressed strongly in tissues such as the lymph nodes, append ix, and spleen. The recombinant protein, which was produced by the bac ulovirus system and purified to homogeneity, was a highly efficient ch emoattractant for certain human T cell lines and a highly potent one f or freshly isolated peripheral blood lymphocytes and cultured normal T cells expanded by phytohemagglutinin and interleukin 2. Unlike most o ther CC chemokines, however, this novel chemokine was not chemotactic for monocytes or neutrophils, suggesting that it is specific for lymph ocytes. From these results, we designated this novel CC chemokine as S LC from secondary lymphoid-tissue chemokine. SLC fused with the secret ed form of alkaline phosphatase (SLC-SEAP) was used to characterize th e SLC receptor. Binding of SLC-SEAP to freshly isolated lymphocytes wa s blocked by SLC (IC50, 0.12 nM) but not by any other CC chemokine so far tested, suggesting that resting lymphocytes express a class of rec eptors highly specific for SLC. By using somatic cell hybrids, radiati on hybrids, and selected yeast and bacterial artificial chromosome clo nes, we mapped the SLC gene (SCYA21) at chromosome 9p13 and between ch romosomal markers, D9S1978(WI-8765) and AFM326vd1, where the gene for another novel CC chemokine termed ELC from EBI1-ligand chemokine (SCYA 19) also exists. Collectively, SLC is a novel CC chemokine specific fo r lymphocytes and, together with ELC, constitutes a new group of chemo kines localized at chromosome 9p13.