REGULATION OF INTERLEUKIN-8 BINDING AND FUNCTION BY HEPARIN AND ALPHA-2-MACROGLOBULIN

Background Increased expression of interleukin-8 (IL-8), a potent neut rophil chemoattractant, is associated with a number of inflammatory di seases. Interleukin-8 binds to the glycosaminoglycan (GAG) heparin and the protease inhibitor alpha(2)-macroglobulin, molecules which regula te the function of a number of cytokines. Heparan sulphate was previou sly shown to enhance neutrophil chemotactic responses to IL-8. Objecti ve The purpose of this study was to investigate the effect of heparin, heparan sulphate and alpha(2)-macroglobulin on IL-8 binding to neutro phils and subsequent functional effects in vitro. Methods The binding of I-125-IL-8 to normal neutrophils at 4 degrees C was studied and the IL-8 induced neutrophil chemotactic response was investigated using m icro-Boyden chambers. Complexation of IL-8 with alpha(2)-macroglobulin was confirmed using gel filtration chromatography. Results Heparin, b ut not heparan sulphate, inhibited the binding of I-125-IL-8 to neutro phils (IC50 = 26 mu g/mL) and IL-8 induced neutrophil chemotactic resp onses (IC50 = 4 mu g/mL). The specific inhibitory effect of heparin wa s apparently due to an interaction with IL-8 which was charge-dependen t, since dextran sulphate had a greater inhibitory effect on chemotact ic responses (IC50 = 2 mu g/mL) and FITC-heparin did not bind to neutr ophils. The heparin-induced inhibition of IL-8 binding and chemotactic responses was reversed in a dose-dependent manner in the presence of alpha(2)-macroglobulin. The binding of I-125-IL-8 to neutrophils in th e presence of alpha(2)-macroglobulin appears to be, in part, through t he specific IL-8 receptor. Conclusion These results point to an anti-i nflammatory role for heparin and a novel, potentially, pro-inflammator y role for alpha(2)-macroglobulin which together indicate the importan ce of cytokine-binding macromolecules in determining net cytokine func tion.