Anti-FcRn mAb ameliorated FNIT in pups delivered from immunized β3^−/−FcRn^+/+ mice. (A) Anti-FcRn mAb (5 mg/kg) was injected into pregnant β3^−/−FcRn^+/+ mice 1 day before IVIG transfusion (1 g/kg). The IVIG level in the pups' sera was detected by enzyme-linked immunosorbent assay. Anti-FcRn antibody blocked IVIG translocation in pregnant β3^−/−FcRn^+/+ mice. Sera from pups delivered from β3^−/−FcRn^+/+ mothers without IVIG treatment were used as a negative control. n = 2-5. (B) Anti-FcRn mAb (5 mg/kg) was injected into pregnant immunized β3^−/−FcRn^+/+ mice once a week until delivery. Anti-FcRn antibody ameliorated thrombocytopenia in affected pups. n = 7-11 for each group.