Antibodies to rat soluble IL‐6 receptor stimulate B9 hybridoma cell proliferation
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abstract
Interleukin‐6 mediates its pleiotropic effects by interacting with its membrane bound receptor (gp80) or the soluble counterpart gp54, resulting in activation of a complex that includes the transducer protein gp130. We have generated a polyclonal antibody against the rat soluble IL‐6 receptor (anti‐rat sIL‐6R) in rabbits. By Western blot analysis we show that purified anti‐rat sIL‐6R IgG antibody reacts specifically with recombinant rat sIL‐6R generated from E. coli, baculovirus or adenovirus expression systems. Anti‐rat sIL‐6R inhibited IL‐6‐induced acute phase protein synthesis in rat (H35) but not human (HepG2) hepatoma cells, and did not affect stimulation of those cells by Oncostatin‐M. Conversely, on the mouse hybridoma B9 cell line, IgG anti‐rat sIL‐6R showed a dose‐dependent stimulation of proliferation. Fab fragments of this antibody did not stimulate, but abrogated IL‐6‐mediated hepatoma cell stimulation and B9 cell proliferation. Gel shift analysis of STAT nuclear factors showed activation of STAT DNA binding in nuclei of B9 cells treated with IgG anti‐rat sIL‐6R, whereas in H35, NIH‐3T3 and M1 cells, only IL‐6 could trigger a similar STAT activation. Our data suggest that mechanisms of IL‐6 receptor activation and signalling in mouse B9 hybridoma cells show subtle but important differences from other IL‐6‐responsive cells.
