STIMULATION OF THE B9 HYBRIDOMA CELL-LINE BY SOLUBLE INTERLEUKIN-6 RECEPTORS

Interleukin-6 (IL-6) exerts its effects by binding to specific recepto rs on the cell surface. The IL-6 receptor consists of at least two com ponents, a ligand binding 80 kDa low-affinity component (IL-6R) and a signal-transducing non-ligand binding 130 kDa component (gp130). The p resence of soluble forms of these components has been described in bot h conditioned media and biological fluids. The soluble (s) IL-6R has b een shown to enhance the IL-6 sensitivity of several both murine and h uman IL-6 sensitive cell types. A sensitive and commonly used method f or measuring biological IL-6 activity is based on the IL-6 dependent p roliferation of the murine hybridoma cell line B9. In this paper, we d emonstrate that recombinant (r) human (h) sIL-6R enhances the sensitiv ity of B9 cells in a dose-dependent manner. The rhsIL-6R enhanced the binding of I-125-rhIL-6 to B9 cells. The rhsIL-6R induced stimulation of B9 proliferation was maximal at 100 ng/ml, even without addition of rhIL-6 and in the presence of anti-hIL-6 antibodies. This may be due to endogenous IL-6 production by the B9 cells, low levels of IL-6 in t he fetal calf serum used, or perhaps an IL-6 independent effect by the rhsIL-6R. In conclusion, this and other reports point to the necessit y of confirming measured biological activities through the use of neut ralizing specific antibodies or parallel measurements in immunochemica l assays.