Vol. 62, Issue 1, 173-180, July 2002

The Unique Property of the CC Chemokine Regakine-1 to Synergize with Other Plasma-Derived Inflammatory Mediators in Neutrophil Chemotaxis Does Not Reside in Its NH₂-Terminal Structure

Mieke Gouwy, Sofie Struyf, Frank Mahieu, Willy Put, Paul Proost, and Jo Van Damme

Laboratory of Molecular Immunology, Rega Institute for Medical Research, University of Leuven, Leuven, Belgium

The recently discovered CC chemokine, regakine-1, is constitutively present in bovine serum and synergizes with the CXC chemokine interleukin-8 (IL-8) to chemoattract neutrophils. Here we show that regakine-1 cooperates with the CXC chemokine receptor 2 ligand neutrophil activating protein-2 (NAP-2) and the anaphylatoxin C5a, two other mediators of inflammation present in the circulation. Neutrophil chemotaxis was 3-fold enhanced when regakine-1 (100 ng/ml) and C5a (30 ng/ml) were combined at concentrations present in bovine or human plasma, respectively. This synergy was also observed when neutrophils were preincubated with regakine-1. Plasma chemokines such as NAP-2, -thromboglobulin, and hemofiltrate CC-chemokine-1 did not affect C5a chemotactic activity. The capability of regakine-1 to synergize with C5a, NAP-2, or N-formyl-methionyl-leucyl-phenylalanine (fMLP) was not observed for monocyte chemotactic protein-3 (MCP-3), another CC chemokine that weakly chemoattracts neutrophils. Regakine-1 also failed to cooperate with MCP-3 and macrophage inflammatory protein-1 in neutrophil chemotaxis. The receptor of regakine-1 is not known yet. Competition with labeled fMLP or C5a for binding to neutrophils or receptor transfected cell lines demonstrated that regakine-1 did not alter receptor recognition. The protein kinase inhibitors 2'-amino-3'-methoxyflavone (PD98059), wortmannin and staurosporin had no effect on the synergy between C5a and regakine-1. Although NH₂-terminal truncation affects the chemotactic potency of most chemokines, it did not affect the synergistic capacity of regakine-1 with C5a on neutrophils. These findings indicate that the constitutive plasma chemokine regakine-1 is a stable enhancer of the inflammatory response and that its blockade might be beneficial in acute and systemic inflammatory disorders.