Effect of down-regulation of insulin receptors on receptor-antibody binding

The extraction of insulin receptor antibody (ARAB) by IM-9 lymphoblastoid cells was measured using nonisotopic ARAB, ARAB extraction was expressed as a clearance, with ARAB determinations made indirectly by a method dependent on its inhibition of insulin binding. Control cells and down-regulated IM-9 cells (cells exposed to 10(-7) M insulin for 16 h) at a cell density of 8 X 10(7) cells/ml were incubated in the presence of a 1:75 dilution of serum from a patient with insulin resistance due to insulin receptor antibodies. After 60 min at room temperature, control cells cleared 42 +/- 3% of ARAB compared to only 18 +/- 2% by the down-regulated cells. ARAB clearance was directly proportional to maximal tracer insulin binding, as determined in parallel experiments. ARAB clearance was similarly reduced in a dose-related fashion by 16-h exposure to Concanavalin A. These results indicate that ARAB extraction by IM-9 cells is reduced by chronic exposure to insulin. The observation that ARAB binding to insulin down-regulated cells is reduced despite the ability of ARAB to attach normally to cells whose receptors have been saturated with insulin supports the notion that down-regulation is due to a loss of membrane receptor rather than to simple receptor occupancy. (Endocrinology 108: 478, 1981)