Gene cloning of a new plasma CC chemokine, activating and attracting myeloid cells in synergy with other chemoattractants

Chemokines are important mediators of cell migration during inflammation an d normal leukocyte trafficking. Inflammatory chemokines are induced in mult iple cell types at sites of infection. Here, we describe a novel bovine CC chemokine, designated regakine-1, that is constitutively present at high co ncentrations in plasma. Cloning of its gene revealed an expected two intron /three exon organization, with a rather long first intron. In addition to a 21-residue signal peptide, the coding sequence corresponded to a 71-residu e secreted protein. However, the natural regakine-1 protein missed the COOH -terminal lysine residue. Regakine-1 has only weak sequence similarity (< 5 0% identical residues) with other animal or human chemokines. Northern blot analysis demonstrated regakine-1 RNA expression in spleen and lung. At phy siological concentrations (30-100 ng/mL), natural 7.5 kDa regakine-1 stimul ated gelatinase B release from neutrophils and chemoattracted immature myel oid HL-60 cells, as well as mature granulocytes. Regakine-1 was more potent on human myeloid cells than the human plasma CC chemokine hemofiltrate CC chemokine-1 (HCC-1). Moreover, regakine-1 synergized with the bacterial pep tide N-formylmethionylleucylphenylalanine (fMLP), yielding a 10-fold increa se in neutrophil chemotactic response above their additive effect. Regakine - I did not compete with interleukin-8 (IL-8) for binding to neutrophils, n or did it affect fMLP-induced calcium signaling, suggesting that regakine-1 recognizes a different receptor. In view of its high constitutive plasma c oncentration, regakine-1 is believed to recruit myeloid cells into the circ ulation, whereas its synergy with other neutrophil chemoattractants suggest s that it also enhances the inflammatory response to infection.