Human recombinant interleukin-1 receptor antagonist blocks bone resorption induced by interleukin-1 beta but not interleukin-1 alpha.

Both interleukin-1 alpha (IL-1 alpha) and interleukin-1 beta (IL-1 beta) are powerful stimulators of bone resorption in vivo and in vitro. Interleukin-1 receptor antagonist (IL-1ra) binds to many interleukin-1 receptors. It does not activate the receptor and effectively blocks the action of IL-1 alpha and IL-1 beta. In this study, human recombinant IL-1ra, at 100-fold excess, was found to block bone resorption in cultured mouse calvaria due to IL-1 beta but not IL-1 alpha. These observations may be explained by differential affinities of receptors for IL-1 alpha, IL-1 beta and rhIL-1ra on target bone cells.