Effects of P1 serum on insulin binding and signaling. (A) Effect of patient 1 serum on ¹²⁵I-insulin binding to IR. Results from 3 independent experiments. (B) Effect of P1’s serum immunoglobulins (100, 200, and 500 μg/mL as indicated) on insulin signaling. Immunoglobulins from 2 control subjects were used at 200 μg/mL for comparison. Activated (phosphorylated) and total forms of the IR β, the insulin receptor substrate-1 (IRS1), the MAP-kinase ERK1/2, and the protein kinase B (Akt-PKB) are evaluated by western blot on lysates from cells incubated or not with insulin, as indicated (see supplemental Methods). Data are representative of 2 independent experiments.