Maternal anti-CD36 antibodies crossed the placenta and caused thrombocytopenia and fetus death. (A) Flow cytometry analysis: (a) circulating anti-CD36 IgG from an immunized Cd36^−/− mother (white curve) was analyzed by using normal mice sera as control (gray curve). (b) Circulating anti-CD36 in the pups’ serum was measured by using pups’ serum from the naive mother as control (black curve). (c) Anti-CD36 IgG bound to pups’ platelets (platelet-binding IgG) was analyzed by using normal pups’ platelets from the naive mother as control (dark gray curve). (B) Platelet counts of pups from naive and immunized Cd36^−/− mothers were counted by flow cytometry using counting beads as standard. The pups’ platelets (29 among 46 survival pups) from Cd36^−/− immunized mothers (cohort #3; n = 7) is significantly decreased compared with pups’ platelets (13 among 24 survival pups) from naive mothers (cohort #2; n = 3). Data are expressed as mean ± standard deviation. Significance (***P < .0001) was analyzed by using a two-tailed unpaired Student t test. (C) Sera from immunized Cd36^−/− mothers (n = 16) were analyzed by using flow cytometry. The reactivity of anti-CD36 antibodies in each maternal serum as relative fluorescence intensity (geometric mean) related to the percentage of mortality (number of dead pups/total pups) in the respective mothers is presented. Significance was analyzed by Pearson analysis (P = .0189; 95% confidence interval, 0.1161-0.8349). MFI, median fluorescence intensity.