Production and secretion of interleukin 1 receptor antagonist in monocytes and keratinocytes

IL-1 receptor antagonist (IL-1ra) is a newly described member of the IL-1 family, isolated from supernatants of Ig stimulated monocytes, that binds competitively to IL-1 receptors without stimulating target cells. Also epithelial cells produce IL-1ra in a form which lacks a secretory signal sequence. Here we have compared the biosynthesis and secretion of IL-1ra in monocytes and keratinocytes. Our data show that monocytes produce two molecular forms of IL-1ra, of 18 Kd and 23 Kd respectively, which differ in the degree of glycosylation. Both forms are secreted via the "classical" endoplasmic reticulum (ER)-Golgi secretory pathway. By contrast keratinocytes produce IL-1ra in a molecular form of 20 Kd, which is not N-glycosylated: 20 Kd IL-1ra is detectable in supernatants of keratinocytes, although in small amounts. The presence of IL-1ra in keratinocytes cultures fluids is not inhibited by Brefeldin A (BFA), suggesting a possible secretion through the leaderless secretory pathway.