Interleukin 1 enhances the development of spontaneous arthritis in MRL/lpr mice.

We previously reported that treatments with human recombinant interleukin-1 beta (rIL-1 beta) in DBA/1 mice which were suboptimally immunized with native chick type II collagen (NcII) markedly accelerated the onset of collagen-induced arthritis (CIA). In the present study, we further characterized this IL-1-mediated enhancement of murine arthritis by examining the in vivo effects of rIL-1 beta in another arthritis model, namely, the spontaneous arthritis of the MRL/lpr mouse strain. The results of these studies demonstrated that IL-1 treatments also enhanced the onset and progression of the spontaneous arthritic disease in MRL/lpr mice. A substantial proportion of the IL-1-treated MRL/lpr mice that were between 3 and 3.5 months of age exhibited swelling in either the hind or front paws. Moreover, histopathologic studies demonstrated the presence of striking alterations within the various joints of these IL-1-treated MRL/lpr mice. Such abnormalities were not detected in the non-IL-1-treated, age-matched MRL/lpr mice. Therefore, as in the experimentally induced disease of CIA, IL-1 may also be capable of contributing to the pathogenesis of the spontaneous arthritis of MRL/lpr mice.