The effect of maternal anti-CD36 antibodies on the fate of pups delivered by immunized Cd36^−/− female mice. (A) Naive Cd36^−/− female mice (n = 5) were bred with WT male mice and delivered pups 3 times. The litter size was documented. One mother (#1) delivered a smaller littermate after the second and third pregnancy (litter size, 1.50 ± 0.71) compared with the other 4 mothers (#2-5) (litter size, 7.50 ± 1.93). Weak CD36-reactive antibodies were detected in mother #1 according to flow cytometry (see inset, the third delivery) but not in mothers #2 to #5 (data not shown). (B) Cd36^−/− female mice (cohort #3) were immunized 3 times with WT platelets. Representative sera were then incubated with platelets from WT (white curves) or Cd36^−/− mice (gray curves). Bound antibodies were detected with fluorescence-labeled anti-mouse IgG and analyzed by using flow cytometry. The percentages of positive cells (anti-CD36) are given. Sera from naive Cd36^−/− were used as controls. (C) After immunization, Cd36^−/− female mice (cohort #3; n = 16) were bred with WT male mice. Naive WT (cohort #1; n = 5) and naive Cd36^−/− (cohort #2; n = 4) were conducted as controls. Dead pups were determined in utero or within 24 hours after delivery. The mortality of the pups in cohort #3 (31 of 77 [40.26%]) was compared with that of cohort #1 (χ² = 17.46; ***P < .0001) and cohort #2 (χ² = 11.52; ***P = .0007). (D) Severe bleeding in Cd36^+/− pups delivered by immunized Cd36^−/− mothers was found. (a) Healthy pup; (b) dead pup with bleeding (arrow); (c) dead pup with ICH (arrow); (d) dead pup with hydrops. (E) The litter size (including the dead pups) in naive WT, Cd36^−/− mothers (cohorts #1 and #2), and immunized Cd36^−/− mothers (cohort #3) is presented. The litter size in immunized Cd36^−/− (cohort #3) was small but not significantly different compared with the naive WT (cohort #1) (4.81 ± 2.69 vs 7.40 ± 2.07; P = .064) and Cd36^−/− (cohort #2) mothers (4.81 ± 2.69 vs 6.25 ± 1.50; P = .323) using a two-tailed unpaired Student t test.