Epitope-function relationships of human leukemia inhibitory factor receptors using a novel set of anti-gp190 mAb

The binding and functional properties of a set of six mAb directed against the human gp190 [leukemia inhibitory factor (LIF) receptor] signal transducing molecule were determined, Each of the antibodies reacted with a distinct epitope on gp190 expressed either by gp190-transfected Chinese hamster ovary cells or by the LIF receptor-positive choriocarcinoma JAR cell line, Two of the antibodies (1B4 and 6E6) had binding stoichiometries that were similar to 2-fold lower than those of other mAb (10B2, 12D9 and 7G7), suggesting either that gp190 is present as a pre-associated homodimer in the cell membrane or that part of gp190 is pre-associated with another component, Two mAb (1C7 and 1B4) were found to inhibit LIF binding on the two cell types studied, On JAR cells, this inhibition was, however, restricted to the high-affinity LIF component, suggesting different modes of LIF engagement with the low-and high-affinity receptor species. mAb 1C7 and 1B4 were also found to synergize for, inhibiting LIF high-affinity binding, This synergy also extended to the inhibition of LIF- or oncostatin M (OSM)-induced proliferation of a Ba/F3 cell line co-transfected with human gp130 and gp190. However, this mAb combination inhibited LIF-but not OSM-induced haptoglobin secretion by HepG2 cells, suggesting that whereas haptoglobin secretion induced by LIF involves gp130/gp190 common LIF/OSM type I receptors, that induced by OSM mainly involves type II OSM receptors.