Development and validation of an IL-6 immuno-receptor assay based on surface plasmon resonance.

Interleukin-6 (IL-6) is a pleiotropic cytokine which interacts with the specific IL-6 receptor at the surface of the T lymphocytes. A combined immuno- and receptor-assay has been developed and validated to characterize the biological activity of recombinant IL-6 (rIL-6). This assay is based on Surface Plasmon Resonance (SPR) technology. From each experiment two successive interactions were monitored: anti-IL-6 antibody/rIL-6 and rIL-6/IL-6 soluble Receptor (sIL-6R). Based on the first interaction an immuno-assay for rIL-6 was optimized and validated. Based on the second interaction a receptor-assay for rIL-6 biological activity was optimized and validated. The assays were validated by performing three different assays on three different days. The intra- and inter-day precisions (%CV) for the immuno-assay were respectively 0.9% and 1.7%. The overall recovery of the immuno-assay was 98.9 +/- 1.6. Intra- and inter-day precisions for the receptor-assay were respectively 1.1% and 1.4%. The overall recovery of the receptor-assay was 99.4% +/- 1.1. This immuno-receptor assay has allowed to compare the rIL-6 stability after storage at different temperatures. The results did not show significant difference between the three lower storage temperatures (-70, -20 and 5 degrees C). However, results obtained for the aliquot stored at 25 degrees C have shown a drastic denaturation of the rIL-6. These results illustrate the advantage of this method combining the evaluation of the immunological and biological integrity of the drug and high reproducibility and precision of the biosensor based technology.