Frequencies of dendritic cells (myeloid DC and plasmacytoid DC) and their ratio reduced in pregnant women: comparison with umbilical cord blood and normal healthy adults.

CD11c(+) peripheral blood myeloid dendritic cells (MDC), and CD123(bright) plasmacytoid cells (PDC), are two human dendritic cell (DC) populations. In the present study, the percentages of MDC [lin(-)/HLA-DR(+)/CD123(-)/CD11c(+)] and PDC [lin(-)/HLA-DR(+)/CD123(bright)] in a peripheral blood (PB) sample obtained from women at the time of delivery and in their umbilical cord blood (UCB) were compared with those in the PB of healthy volunteers. The percentages of MDC and PDC were determined by four-color flow cytometry. The percentages of MDC and PDC were significantly lower in the PB obtained at delivery (MDC, 0.11% +/- 0.08%; PDC, 0.06% +/- 0.06%) and in the UCB (MDC, 0.15% +/- 0.03%; PDC, 0.05% +/- 0.05%) than in the PB of the controls (males, 0.28% +/- 0.12%, 0.11% +/- 0.06%; females, 0.32% +/- 0.13%, 0.11% +/- 0.07%). Among the pregnant women at delivery, there were significant correlations between the percentage of MDC or percentage of PDC in the PB at delivery and the respective parameter in the UCB. The PB of other pregnant women, at 20-35 weeks of gestational age, also indicated significantly low percentages of MDC and PDC (0.1% +/- 0.1%, 0.06% +/- 0.07%). The ratio of MDC/PDC was not reduced in the UCB (4.25 +/- 2.74), but was reduced in the PB obtained at delivery and the PB obtained during pregnancy (0.79 +/- 0.91) in comparison with that in age-matched, nonpregnant females (3.96 +/- 2.95). It was assumed that reduction of MDC during pregnancy plays an important role in maintaining immune tolerance against the embryo.