Distinct classes of chaperoned IL-6 in human blood: differential immunological and biological availability

Transport of IL-6 in blood is fundamental to the biology of this cytokine. In the present study, IL-6 transport, immunological reactivity, and biological availability were investigated in blood from melanoma patients subjected to different active specific immunization regimens (an anti-idiotypic mAb immunization protocol (mAb-keyhole limpet hemocyanin (KLH)-Calmette-Guerin bacillus (BCG), an autologous anti-cancer vaccine protocol (AAAP), or both). Sera were subjected to Sephadex G-200 gel filtration chromatography, and the structure and biological activity of IL-6 complexes in the eluate fractions were probed using five IL-6 ELISAs and two bioassays. Sera from patients administered mAb-KLH+BCG followed by AAAP contained three distinct classes of IL-6 eluting at 30, 200, and 450 kDa, each with its characteristic ELISA reactivity and bioactivity: the 30- and 450-kDa complexes were bioactive in the B9 and Hep3B assays, but the 200-kDa complex was not. The 30- and 450-kDa IL-6 complexes were preferentially reactive in the 7IL6/5IL6 ELISA, the 200-kDa IL-6 complexes were preferentially reactive in the 4IL6/5IL6 ELISA, while the three commercial ELISAs (R&D, Endogen, and Genzyme) detected essentially only the 30-kDa IL-6. In contrast, 1) sera from AAAP patients contained biologically active 30- and 450-kDa IL-6 complexes, while 2) sera from mAb-KLH+BCG patients contained 200-kDa IL-6 complexes inactive in ex vivo bioassays. Both the 450- and 200-kDa complexes included soluble IL-6R, with the 200-kDa complexes additionally containing ligand-occupied anti-IL-6 and anti-soluble IL-6R IgG. The data indicate the existence of specific mechanisms that regulate the transport and function of IL-6 in vivo.