Differential activity of interleukin 1α and interleukin 1β in the stimulation of the immune response in vivo

Abstract

The biological activities of human recombinant interleukin (IL) 1α and IL 1β were compared in different biological systems. The two IL 1 forms were equally active in vitro in inducing proliferation of murine thymocytes and of the murine T helper clone D10.G4.1, and in triggering release of prostaglandin E₂ from human skin fibroblasts. In vivo, IL 1α and IL 1β were similarly pyrogenic both in rabbits and mice, and could equally increase the circulating levels of the acute phase protein serum amyloid A in mice. However, only IL 1β showed immunostimulatory activity in vivo, as it could enhance the number of specific antibody‐producing cells in the spleen of mice immunized with either a T‐dependent or a T‐independent antigen. Although devoid of immunostimulatory activity, IL 1α could efficiently compete immunostimulation induced by IL 1β, suggesting an effective interaction with the IL 1 receptor. Thus, IL 1β appears to have an important role in the positive regulation of immune responses, while IL 1α may act as down‐regulator of the IL 1β effect.