ER stress–induced IICR in vivo. (a) WT and Chop^−/− mice were injected with vehicle or 0.02 mg/kg tunicamycin (TUN). 16 h later, peritoneal macrophages were harvested and assayed within 30 min for CHOP, ERO1-α, and β-actin expression by immunoblotting (inset) or for IICR (*, P < 0.001; **, P < 0.05). The arrow indicates ATP addition. (b) Macrophages from WT and ob/ob mice were analyzed for Chop mRNA by RT-QPCR (*, P < 0.05). (c) Macrophages from WT and ob/ob mice were analyzed for IICR as in panel a (*, P < 0.01; and **, P < 0.05). (a–c) Error bars show SEM (n = 3).