Fetal cells in the maternal circulation: detection by direct AFP-immunofluorescence

Ratio of fetal to maternal DNA is less than 1 in 5000 at different gestational ages in maternal blood

Using Southern hybridization with the DNA probe pY3.4, we were not able to detect fetal DNA in blood of 36 pregnant women carrying male fetuses. Gestational ages ranged from 8-40 weeks of pregnancy. Using the same DNA probe, we were able to detect the male-specific signal in experimental dilution series down to 1/5000 on autoradiograms. We conclude that the ratio of fetal DNA in maternal circulation, in contrast to previous estimations, must be lower than 1/5000.

Analysis of peripheral maternal blood samples for the presence of placenta-derived cells using Y-specific probes and McAb H315

Using flow cytometry, a small number of cellular elements expressing on their surface an antigen (H315) produced by placental trophoblast have been observed in the peripheral blood of pregnant women. This is in agreement with previous observations (Covone et al., 1984a,b) and recent results documenting the presence of a small number of H315-positive cells in the peripheral circulation of pregnant women (Pool et al., 1987; Caligaris-Cappio and Camaschella, personal communication). When DNA extracts, prepared from H315-positive cells sorted from maternal samples were tested by Southern transfer using Y-specific probes (Y190 or Y411), a Y-specific band could not be detected in any sample analysed, irrespective of the sex of the fetus. In control samples from healthy male donors, a Y-specific band could be detected with as few as 800 46,XY cells without interference from contaminating 46,XX cells. H315-positive cellular elements, sorted by flow cytometry from the maternal peripheral blood, were also examined in interphase using Y-specific probes (Y190 and Y431) and an in situ biotin-avidin fluorescent hybridization technique. The great majority of the sorted H315-positive cellular elements did not show a fluorescent Y body, even in samples from mothers who later delivered a male infant. While previous investigations had failed to demonstrate the in vitro uptake of H315 antigen onto the surface of leucocytes from healthy males incubated in maternal sera, the present studies demonstrate that cells from male donors could adsorb this antigen following incubation in extracts prepared from retroplacental blood. These findings thus suggest that the majority of H315-positive nucleated cells previously detected by flow cytometry in the peripheral circulation of pregnant women are maternal cells which have adsorbed H315 antigen in vivo, either in soluble form or as small cell membrane fragments.