Fetal origin of amniotic fluid polymorphonuclear leukocytes

OBJECTIVE: Although polymorphonuclear leukocytes are the inflammatory cells most frequently recovered from the amniotic cavity in cases of suspected intrauterine infection, the source of these cells has not been definitively determined. We took advantage of the gender difference between the mother and her male fetus, and we report four cases in which amniotic fluid polymorphonuclear leukocytes were identified as fetal by fluorescence in situ hybridization with probes specific for X and Y chromosomes. Fetal membranes were intact at the time amniotic fluid was obtained in all cases. STUDY DESIGN: Amniotic fluid was obtained from women with male fetuses in premature labor with clinical or laboratory evidence of infection. Cytospin preparations of amniotic fluid samples with polymorphonuclear leukocytes were prepared and sequentially stained with fluorescent reagents. To determine which cells were polymorphonuclear leukocytes, all replicate samples were stained with the fluorescent nuclear stain 4'-6-diamidino-2-phenyl-indole. This allowed definition of the characteristic multilobed polymorphonuclear leukocytes nuclear morphologic features. The sample was then probed with a rhodamine-labeled probe specific for the X chromosome and a fluorescein-labeled probe specific for the Y chromosome to assess whether the polymorphonuclear leukocytes were male or female. RESULTS: Ninety percent to 99% of polymorphonuclear leukocytes identified by normal multiple lobed nuclear morphologic study on 4'-6-diamidino-2-phenyl-indole staining had an X and Y chromosome and were therefore fetal cells. CONCLUSION: These data demonstrate a fetal response during intraamniotic infection. Further investigation of the roles for maternal and fetal polymorphonuclear leukocytes in chorioamnionitis may provide valuable information about the critical interaction of the two immune responses in this setting.