A Novel Human CC Chemokine PARC That Is Most Homologous to Macrophage-Inflammatory Protein-1α/LD78α and Chemotactic for T Lymphocytes, but Not for Monocytes

By searching the expressed sequence tag (EST) database, we identified partial cDNA sequences encoding a polypeptide with significant sequence identity to the human CC chemokine macrophage-inflammatory protein-1α (MIP-1α)/LD78α. We determined the complete cDNA sequence that contained a reading frame of 89 amino acids with 61% identity to human MIP-1α/LD78α. The mRNA was expressed constitutively at high levels in human lung and at low levels in some lymphoid tissues. Furthermore, the mRNA was strongly induced in several human cell lines, including monocytic U937 cells, by PMA. From these results, we designated this novel CC chemokine as PARC from pulmonary and activation-regulated chemokine. In situ hybridization analyses showed that alveolar macrophages, follicular dendritic cells in the germinal centers of regional lymph nodes, and peripheral blood monocytes stimulated with LPS express PARC mRNA. Using the human CC chemokine yeast artificial chromosome contig that we constructed recently, we mapped the PARC gene (SCYA18) within one of the two subregions of the CC chemokine gene cluster at chromosome 17q11.2. To investigate its biologic activity, the PARC protein was expressed in insect cells. PARC was chemotactic for both activated (CD3⁺) T cells and nonactivated (CD14^-) lymphocytes, but not for monocytes or granulocytes. Binding analysis using PARC fused with alkaline phosphatase-(His)₆ showed the presence of a single class of receptors for PARC on lymphocytes with a K_d of 1.9 nM and 590 sites/cell. Thus, PARC is a novel CC chemokine with a close phylogenic relationship with MIP-1α/LD78α, but with a highly selective activity on lymphocytes.