Yellow arrowheads indicate sites of injury. (A) Representative images of FM4-64 dye influx before (0 seconds) and after (60 seconds) injury at baseline (Basal) or after addition of IIM patient sera, IIM patient sera depleted of TRIM72 autoantibodies, and exogenous delivery of purified Hu anti-TRIM72 recovered from IIM patient sera. Scale bars: 20 μm. (B) Sarcolemmal resealing kinetics measured every 3 seconds for 60 seconds as depicted in A. Data are represented as mean ± SEM. (C) AUC calculations of B. (n = 52, 48, 52, and 51 for Basal, Depleted serum, IIM serum, and Purified Hu anti-TRIM72, respectively. ANOVA, F(3,200) = 48.16, P < 0.0001; Tukey’s test: Basal vs. Depleted serum, P = 0.95; Depleted serum vs. Purified Hu anti-TRIM72, P < 0.0001; Depleted serum vs. IIM serum, P < 0.0001.) Data are representative of 3 IIM patient serum samples depleted of TRIM72 autoantibodies. Data are represented as the mean ± SD.