An interleukin 1 like factor stimulates bone resorption in vitro

Abstract

Many activities are now ascribed to the monokine interleukin 1¹ including enhancement of immune responses, stimulation of thymocyte proliferation², activation of B cells³, stimulation of proteinase and prostaglandin production by connective tissue cells⁴, stimulation of the production of acute phase proteins⁵, induction of fever⁶ and the induction of neutrophilia⁷. These activities were thought to be due to various different factors, but are now considered probably due to very similar, if not identical, molecules^8–11. The term interleukin 1 (IL-1) was coined to describe the factor released by monocyte/macrophages which acts on T and B lymphocytes. Only after this definition had been accepted was it shown that target cells other than lymphocytes were affected by IL-1. Products of human blood monocytes (mononuclear cell factor, MCF) have been implicated in the pathogenesis of inflammatory diseases such as rheumatoid arthritis and periodontal disease^12,13. Bone resorption is often a feature of such diseases, and monocytes are frequently found at sites of localized bone resorption. Preliminary experiments with monocyte-conditioned medium indicated that MCF could stimulate bone resorption¹⁴. We therefore undertook this study to verify these observations and to determine whether purified IL-1 could stimulate connective tissue breakdown in vitro.