Identification of IL-1 inhibitory activity as IL-1 receptor antagonist (IL-1ra) in vitro and kinetics of IL-1ra and IL-1 beta in experimental rabbit lung granuloma.

This study investigated whether interleukin-1 (IL-1) inhibitory activity in LPS-stimulated culture supernatants of alveolar macrophages and epithelioid cells obtained from rabbit lung granulomas induced by complete Freund's adjuvant (CFA) was identical to IL-1 receptor antagonist (IL-1ra) and examined the changes of IL-1ra and IL-1 beta levels in lung tissue during the natural course of granulomatous inflammation. In the thymocyte proliferation assay, prostaglandin E2 (PGE2)-free culture supernatants from each cell population revealed a bell-shaped IL-1 titration curve with IL-1 activity suppressed at dilutions of 1:1 to 1:2, and gel chromatography of serum-free culture supernatants showed an IL-1 inhibitory peak at 21-25 kD. Suppression of IL-1 activity in the supernatants at lower dilutions and the gel-purified IL-1 inhibitory activity both almost disappeared after IL-1ra depletion with an anti-rabbit IL-1ra immunoaffinity column, indicating that IL-1ra was responsible for this in vitro IL-1 inhibitory activity. Pulmonary tissue levels of IL-1 beta pecked at 24 h (52.0 +/- 9.5 pg/mg) after CFA injection, whereas IL-1ra levels peaked at 4 weeks (23.1 +/- 4.0 ng/mg) when granuloma development was maximal, and the molar excess of IL-1ra to IL-1 beta peaked from 4 weeks onward at over 800-fold. These observations suggest that IL-1ra may be effective for IL-1 regulation, especially in the later stage of granulomatous responses. Immunohistochemical studies demonstrated that the cellular source of IL-1ra within the pulmonary granulomas was mainly epithelioid cells.