Interaction of the Monoclonal AntibodiesαlR-1 andαIR-3 with Insulin and Somatomedin-C Receptors

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Abstract
.alpha.IR-3, a monoclonal antibody that interacts with the somatomedin-C receptor, inhibited the binding of somatomedin-C, but not of insulin, to human placental membranes and intact IM-9 cells. .alpha.IR-1, monoclonal antibody that interacts with the insulin receptor, did not inhibit the binding of either hormone. Inhibition of somatomedin-C binding by .alpha.IR-3 was mainly due to a decrease in its affinity. 125I-Labeled .alpha.IR-3 bound specifically to placental membranes and intact IM-9 cells and was inhibited by concentrations of unlabeled .alpha.IR-3 that were lower than those required to inhibit somatomedin-C binding. [125I].alpha.IR-3 binding was also inhibited by somatomedin-C and insulin, but only at very high concentrations. A410, a rabbit antiserum that reacts with both receptors for insulin and somatomedin-C, also inhibited labeled .alpha.IR-3 binding. .alpha.RI-1 did not. These results help to define the epitopes with which these antibodies interact.

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