A rapid bioassay for recombinant interleukin-22.

Interleukin-22 is a novel cytokine produced mainly in activated T cells. The elaborate biological functions of IL-22 in vivo are still widely unknown. In this report, we describe a rapid, simple, and reproducible in vitro cell-based bioassay for measuring the bioactivity of recombinant interleukin-22 (IL-22) to study the primary function of IL-22 in vivo. Human hepatocyte cell line (HepG2) was transfected with pSTAT3-Luc, a plasmid carrying the luciferase gene under the control of STAT3. After screening and selection, one stable clone was established which generates a strong response to recombinant human IL-22 (rhIL-22) stimulation in a dose-dependent manner. The cell showed ED50 of 17.0 +/- 1.4 ng/mL (n = 15) to recombinant human IL-22. Pre-incubation of anti-IL-22 mAb with IL-22 recombinant proteins completely blocked the bioactivities. The assay can be completed within one day. The current assay provides a rapid analytical method to measure the biological activity of IL-22 in vitro.