Production of IL-6 by hACs: effects of IL-1β, IL-1F8, heat-inactivated IL-1F8 and anti-IL-1Rrp2 antibodies. (a) Analysis of the effects of IL-1β (1 ng/ml), IL-1F8 and heat-inactivated IL-1F8 (5 mg/ml) on IL-6 production by hACs after 48 hours treatment, as detailed under Materials and method. (b) Analysis of the effects of anti-IL-1Rrp2 antibodies on IL-6 production by hACs. Cells were stimulated or not (control) for 48 hours with IL-1F8 (5 mg/ml) or IL-1b (1 ng/ml), as indicated, in the presence (black columns) or absence (white columns) of blocking anti-IL-1Rrp2 antibodies (10 mg/ml). P < 0.05 versus control; #P < 0.05 versus 5 μg/ml IL-1F8, as determined by analysis of variance. hAC, human articular chondrocyte; IL, interleukin; IL-1Rrp2, IL-1 receptor related protein 2.