Maternal and fetal microchimerism in granulocytes

Cell trafficking during pregnancy may result in durable microchimerism, both fetal microchimerism in the mother and maternal microchimerism in her children. Whether microchimerism is continuously replenished has not been well-described. To address this question, we isolated granulocytes, cells with relatively short half-lives, from peripheral blood of healthy women. CD66b-positive cells were isolated by fluorescence activated cell sorting and a panel of polymorphism-specific quantitative pCR assays was employed to investigate fetal and maternal microchimerism. Overall 33% (10/30) of study subjects had at least one source of microchimerism in CD66b(+) cells. Interestingly, maternal microchimerism was more common than fetal microchimerism, 40% vs. 15%, respectively (p = 0.05) and was present at higher levels (p = 0.03). The identification of maternal and fetal origin CD66b(+) cells is strong evidence for an active microchimeric hematopoietic stem and progenitor cell niche. Furthermore, microchimeric CD66b(+) cells could have an impact on innate and adaptive immune responses.