Identification of a monoclonal antibody which can distinguish between two distinct species of the type I receptor for insulin-like growth factor.

A monoclonal antibody was identified which equally inhibits 125I-labeled insulin and insulin-like growth factor I (IGF-I) binding to their respective receptors in human IM-9 lymphoid cells and solubilized placenta receptor preparations. In contrast, this monoclonal antibody inhibits insulin but not IGF-I binding to human hepatoma (HepG2) cells, fibroblasts and muscle cells. These results indicate that there are two distinct species of the type I insulin-like growth factor receptor (which we have named type IA and type IB) and suggest that this monoclonal antibody may be useful in determining whether different biological effects are mediated through these two receptors.