IL1B and rheumatoid arthritis: Because the effect of IL-1 on cells depends significantly on the relative serum concentration of soluble IL-1β receptors and cytokine, the serum contents of IL-1β (Figure 5) and soluble IL-1β receptors types 1 and 2 (Figures 6 and 7) were studied by ELISA in RA patients in the acute phase and RA patients who responded to treatment.