Persistence of neonatal thrombocytopenia in singly alloimmunized female mice. (A) Maternal anti-APLDQ alloantibody (n = 3 mice per group) titer persists for the duration of 4 serial matings (over an ∼24-week period). Control is plasma from nonimmunized mice. (B) Circulating maternal anti-APLDQ alloantibody levels in the blood of neonatal pups (n = 11-30 mice per group) is present in all 4 serial litters of pre-immunized BALB/c female mice. Control is anti-APLDQ antibody levels in the pups of nonimmunized females. (C) Platelet counts (n = 11-30 mice per group) of all neonates in each litter born to 3 female BALB/c mice that had been pre-immunized with APLDQ murine platelets and then serially bred 4 times with APLDQ homozygous males. Note that the platelet counts of the neonatal mice was as low after the fourth litter as it was in the first litter. Control is neonatal platelet count of pups of nonimmunized females. (D) Representative bleeding in pups born to APLDQ pre-immunized WT BALB/c females crossed with APLDQ homozygous males. The pups are thus heterozygous for the paternally derived APLDQ humanized form of GPIIIa, with the other allele being maternally derived WT murine GPIIIa. Data are presented as mean ± SEM. *P < .05; **P < .001.