Читать книгу Genetic Disorders and the Fetus - Группа авторов - Страница 117

Few nucleated cells in second‐trimester amniocentesis fluids are capable of in vitro attachment and growth, even though many exclude trypan blue. These are cells with pale cytoplasm and small, densely staining nuclei.^{548, 549} Exfoliation of such cells from the fetal epidermis has been directly observed.⁵⁵⁰ It is not known why their number in a given fluid is so highly variable and whether this reflects the wellbeing of the fetus, for which other properties of the AF may be more predictive.⁵⁵¹ Since the change of the fetal skin from a simple two‐layered structure to mature stratified epithelium takes place around the 16th week and occurs at different rates in different body zones, minor differences in gestational age might account for comparatively large differences in overall cornification and desquamation.⁵⁵² Classic cytology and transmission or scanning electron microscopy have attempted a subdivision of cells in midtrimester fluids.^{550, 553–555}

A variable number of cells attach to the culture substrate within 6–72 hours after incubation but the number of colony‐forming cells rarely exceeds 10 cells/mL fluid.^{556, 557} Cells that attach in less than 24 hours (rapidly adhering or RA cells), if present in clear fluids in large quantities, may indicate an NTD.⁵⁵¹ Such cells often take on the characteristic elongated spindle‐like appearance of neural crest cells in monolayer culture. In AFC cultures from NTD pregnancies, the RA cells include monocytic cells that have phagocytic activity and cells of glial origin that lack phagocytic activity and stain positive for synaptophysin and neuron‐specific enolase.^{558, 559} Rapidly adhering, phagocytic, esterase‐ and Fc receptor‐positive cells are also found in AF from normal fetuses, albeit in more moderate quantities.⁵⁶⁰

In cases of abdominal wall defects, macrophage‐like cells and even lymphocyte‐like cells responding to PHA have been described.⁵⁶¹ AF from distressed fetuses may likewise contain macrophage‐like cells, termed fetal distress (FD) cells.⁵⁶² Such FD cells occur in spontaneous abortion, severe intrauterine growth retardation, and preeclampsia. They may originate from the placenta.⁵⁶³