IL-1 receptor antagonist (IL-1ra) expression, function, and cytokine-mediated regulation during mycobacterial and schistosomal antigen-elicited granuloma formation.

Abstract

Granulomas (GR) mediated predominantly by Th1/type 1 (IFN-gamma) and Th2/type 2 (IL-4, IL-5, IL-10) cytokines were induced by i.v. injection of sensitized CBA/J mice with carbohydrate beads coated with Mycobacterium tuberculosis or Schistosoma mansoni egg Ags, respectively. GR macrophages (Mphi) from types 1 and 2 GR both produced IL-1ra, but the former showed accelerated IL-1ra-producing capacity, releasing two- to threefold greater amounts on day 4 than those of type 2 GR, as measured by sandwich ELISA. In vivo depletion of IL-1ra exacerbated GR size and augmented regional cytokine production in both types of responses. To determine the critical cytokines mediating IL-Ira expression, oil-elicited peritoneal Mphi were exposed to graded doses (0.1 to 10 ng/ml) of cytokines (IL-1beta, IL-2, IL-4, IL-10, IL-12, IFN-gamma, and TNF-alpha) for 24 h, then stimulated with opsonized zymosan. Of the cytokines tested, IFN-gamma and TNF-alpha were the best costimuli for IL-1ra production in the presence of zymosan, whereas IL-1beta, IL-10, and IL-12 were not active. In vivo depletion of IL-4, IL-10, IL-12, IFN-gamma, or TNF-alpha with 5 mg of cytokine-specific neutralizing rabbit IgG revealed that IFN-gamma and TNF-alpha were required for maximal IL-1ra production by Mphi. Furthermore, the delayed IL-1ra production by type 2 GR Mphi could be related to later TNF-alpha production. Our findings indicate that IL-1ra is a common regulatory product of inflammatory Mphi and is particularly promoted by type 1 cytokines, IFN-gamma, and TNF-alpha.