IL-1 is a mediator of the acute inflammatory response and plays a key role in influencing growth and differentiation of immunocompetent lymphocytes. It can enhance transcription and secretion of the T-cell growth factor interleukin-2 (IL-2) and can stimulate the expression of membrane receptors for IL-2. However, the regulation and control of IL-1 activities are poorly understood. Recently an IL-1 inhibitor, interleukin-1 receptor antagonist (IL-1 ra), has been described and cloned. This protein is a monokine originally found in the urine of febrile patients and in supernatants of human monocytes adhering to an IgG-coated surface, with an approximate molecular weight of 17 kDa, which is similar to IL-1-beta but having no IL-1-like activity and antagonizing IL-1 by binding to its cell surface receptor. These studies have examined some biological properties of hrIL-1ra, such as its effects on the secretion of IL-1-alpha or IL-1-beta and IL-2, the surface expression of IL-2R and DNA synthesis by peripheral blood mononuclear cells (PBMC). PBMC from normal volunteers were separated and used at a concentration of 2.5 x 10(6) cells/ml. The cells were pretreated for 2 h with hrIL-1ra (0.025-250 ng/ml), treated with LPS (10 ng/ml), and IL-1-alpha and IL-1-beta secretion were determined by an ELISA method. In addition the influence of hrIL-1ra (25 ng/ml) on IL-2 generation was determined. In another set of experiments, flow cytometric analysis with an anti-CD25 monoclonal antibody was determined on PHA-stimulated PBMC pretreated with hrIL-1 ra (2 h) and cultured for 48 h. The inhibition by hrIL-1ra of IL-2R expression was dose-dependent and when hrIL-1ra was used at 250 ng/ml the IL-2R was completely abolished. Lymphocyte DNA synthesis calculated from the net uptake of [H-3]-thymidine (H-3-TdR) was also inhibited by hrIL-1ra (0.025-25 ng/ml). In this report we found that hrIL-1ra inhibits, in a dose-dependent manner, the secretion of IL-1-alpha, IL-1-beta, IL-2, the surface expression of IL-2R and H-3-TdR incorporation in PBMC in vitro. These data suggest a new biological activity of hrIL-1ra and further extend the immunomodulatory potential and significance of this new cytokine. The action of IL-1ra on modulating the synthesis of IL-1 may be of paramount importance in the regulation of these effects.
