Species-Specific Activity of Rat Recombinant Interleukin-1β

We have constructed expression clones for mature rat interleukin-1β (IL-1β). Using these clones, rat recombinant IL-1β (rrIL-1β) was prepared and purified by a single-step cation-exchange chromatography method. In addition, synthetic rrIL-1β mRNA was transcribed and used to synthesize radiolabeled ³⁵S-rrIL-1β for binding studies. The rrIL-1β produced was demonstrated to have IL-1 bioactivity in a mouse thymocyte proliferation assay, in which it could be blocked by inclusion of human recombinant IL-1 receptor antagonist (hrIL-1Ra). Similarly, rrIL-1β induced LIF mRNA expression in cultured rat sympathetic ganglia. In each case, the maximal dose of rrIL-1β was similar to that of human IL-1β. However, the peak response in rat tissue was twofold higher with rat IL-1β than with human IL-1β. The expression of rrIL-1β provides a useful tool for studying IL-1 receptors in rat, in which human and mouse IL-1β have been found to bind poorly. Species-specific activity of rat IL-1β may correlate with compensatory ionic properties of rat IL-1 receptor.