Plasma MWReg30 pharmacokinetics following IVIG treatment. MWReg30 was administered by intraperitoneal infusion (0.99 μg/d × 7 days), and IVIG was given by intraperitoneal bolus injection at 96 hours. MWReg30 concentrations were determined via ELISA. Symbols represent treatment groups (n = 5 mice/group) receiving saline (•) or IVIG at doses of 0.4 g/kg (▪), 1 g/kg (♦), or 2 g/kg (▴). IVIG treatment altered the pharmacokinetics of MWReg30, decreasing MWReg30 exposure. This finding is consistent with the hypothesis that high-dose IVIG therapy leads to inhibition of the IgG transporter FcRn.