INTERLEUKIN-6 FAMILY OF CYTOKINES INDUCED ACTIVATION OF DIFFERENT FUNCTIONAL SITES EXPRESSED BY GP130 TRANSDUCING PROTEIN

Gp130 transducing protein was shown to be involved in the formation of the high affinity receptors for interleukin 6 (IL-6), interleukin-11 (IL-11), leukemia inhibitory factor, oncostatin M (OSM), ciliary neuro trophic factor (CNTF), and cardiotrophin-1. In the present study we ha ve characterized the functional properties of antibodies directed agai nst this protein and identified a group of monoclonal antibodies able to antagonize the biological activities of all the cytokines belonging to the IL-6 cytokine family, The B-R3 pan-blocking antibody weakly in terfered with the binding of the radiolabeled ligands (with the except ion of OSM, whose binding was abrogated in the presence of B-R3 monocl onal antibody) but inhibited the gp130 homodimerization or its associa tion with gp190/leukemia inhibitory factor receptor, as well as the su bsequent tyrosine phosphorylation events, In addition we identified an tibodies that were able to neutralize only one single cytokine of the IL-6 family, This was the case for the B-K5 antibody, which antagonize d the binding of OSM to gp130 but did not interfere with the signals p rovided by the related cytokines triggering the proliferation of the T F1 erythroleukemia cell line or the induction of haptoglobin synthesis in the HepG2 hepatoma cell line, Similarly, we also characterized two additional antibodies B-P8 and B-P4, which inhibited the TF1 cell pro liferation observed in the presence of CNTF and IL-11, respectively, B -P8 antibody only faintly interfered with the binding of the gp130-lig ands and might modulate the signal transduction pathways, This study i ndicates that in addition to functional site(s) required by the whole family of IL-6 type cytokines to transduce the signal insight the cell , specific cognate functional sites were recruited by OSM, CNTF, or IL -11.