CCL-21 (6Ckine)

6Ckine is a novel CC chemokine discovered independently by three groups from the EST database. 6Ckine, also named SLC (secondary lymphoidtissue chemokine), CCL21 and Exodus2, shows 21-33% identity to other CC chemokines. 6Ckine contains the four conserved cysteines characteristic of β chemokines plus two additional cysteines in its unusually long carboxy-lterminal domain. Human 6Ckine cDNA encodes a 134 amino acid highly basic precursor protein with a 23 amino acid residue signal peptide that is cleaved to form the predicted 111 amino acid residue mature protein. Mouse 6Ckine cDNA encodes a 133 amino acid residue protein with a 23 residue signal peptide that is cleaved to generate the 110 residue mature protein. Human and mouse 6Ckine share 86% amino acid sequence identity. 6Ckine is constitutively expressed at high levels in lymphoid tissues such as lymph nodes, spleen and appendix. In mouse, high levels of 6Ckine mRNA are also detected in the lung. Unlike most CC chemokines, 6Ckine is not chemotactic for monocytes. Recombinant mouse 6Ckine is chemotactic in vitro for thymocytes and activated T cells. Recombinant human 6Ckine has been shown to be chemotactic for some human T cell lines, resting PBL, and cultured T cells expanded with PHA and IL2. 6Ckine has also been reported to inhibit hemopoietic progenitor colony formation in a dosedependent manner. 6Ckine acts via the CC receptor CCR7 on T cells and B cells.