Takahara Yoshiyuki

Analysis of interleukin 6 (IL-6)/IL-6 receptor system using monoclonal anti-IL-6 antibodies

Abstract To investigate the IL-6/IL-6 receptor system, we obtained five murine monoclonal antibodies against human IL-6, which neutralize its biological activity. We classified them into two groups (Type I mAb and Type II mAb) according to the epitopes they recognized. These two types of antibodies showed no difference in the manner in which they neutralized IL-6 activity, but they differed in the way they inhibited the binding of IL-6 to its receptor. While Type I mAb inhibited IL-6 binding to its receptor completely, Type II mAb inhibited only partially, even at a concn of Type II mAb sufficient to neutralize biological activity. Scatchard plot analysis revealed that in the case of the human myeloma cell line, the U266 cell, which showed two-phase binding of IL-6 to its receptor, the high affinity binding disappeared and the affinity of the low affinity binding decreased in the presence of Type II mAb. These results suggest that Type I mAb neutralizes IL-6 activity by the blocking of IL-6 binding to its receptor directly. In contrast, Type II mAb neutralizes IL-6 activity not by direct blocking of IL-6 binding to its receptor, but by modulating the binding affinity of IL-6 to its receptor, that is, inhibiting the formation of high affinity binding in IL-6 receptor system. This also indicates that the formation of high affinity binding may be necessary to transduce the IL-6 signal.