Transplacental Alloimmunization to Fetal Erythrocytes in Rhesus Monkeys (Macaca mulatta)

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Abstract
Evidence of transplacental immunization in rhesus monkeys was obtained by testing postpartum sera from 252 females for antierythrocyte agglutinins. One‐third of the sera contained antibodies reactive with the mates' or the newborns' cells. Fetal erythrocytes were detected in the maternal circulation as early as 8 weeks after conception and as late as 12 days postpartum. Maternal antibodies were detected as early as 2 months after conception and persisted for more than 3 weeks postpartum. It was concluded that the fetal cells stimulated antibody production. Several features of transplacental immunization differ between rhesus monkeys and humans. A parity effect was not observed in rhesus. In fact, 33% of primiparous rhesus females produced antibodies. Also, several of the different allogeneic blood group factors appeared to be immunogenic but differed in immunopotency. Finally, direct antiglobulin tests indicated that erythrocytes of 11% of newborns were coated with maternal antibodies. Nevertheless, in contrast to humans, hemolytic disease was not observed.