Context During pregnancy, fetal CD34+ cells enter the maternal circulation,
persist for decades, and create a state of physiologic microchimerism. Many
studies have confirmed the residual presence of fetal cells in maternal blood
and tissues following pregnancy. Fetal cells may respond to maternal injury
by developing multilineage capacity in maternal organs.
Objective To verify that fetal microchimeric cells express markers of epithelial,
leukocyte, and hepatocyte differentiation within maternal organs.
Design, Setting, and Patients Archived paraffin-embedded tissue section specimens from 10 women who
had male offspring and were previously found to have high numbers of microchimeric
cells, and 11 control women who had no prior male pregnancies. Male cells
were identified by fluorescence in situ hybridization, using X and Y chromosome–specific
probes, followed by histologic and immunochemical studies using anticytokeratin
(AE1/AE3) as a marker of epithelial cells, anti-CD45 as a leukocyte marker,
and heppar-1 as a hepatocyte marker.
Main Outcome Measure Percentage of microchimeric cells expressing nonhematopoietic markers.
Results A total of 701 male (XY+) microchimeric cells were identified (mean
[SD], 227  XY+ cells per million maternal cells). In maternal epithelial
tissues (thyroid, cervix, intestine, and gallbladder), 14% to 60% of XY+ cells
expressed cytokeratin. Conversely, in hematopoietic tissues, such as lymph
nodes and spleen, 90% of XY+ cells expressed CD45. In 1 liver sample, 4% of
XY+ cells expressed heppar-1. Histologic and immunochemical evidence of differentiation,
as assessed by independent observers, was highly concordant (κ = 0.72).
Conclusion The detection of microchimeric male cells, bearing epithelial, leukocyte,
or hepatocyte markers, in a variety of maternal tissue specimens suggests
the presence of fetal cells that may have multilineage capacity.