The comparison of microglia maturation in CNS of normal human fetuses and fetuses with Down's syndrome.

The study was performed on the tissues derived from the central nervous system (CNS) of 72 normal human fetuses between 8 and 22 week of gestation (GW) and 30 fetuses with genetically confirmed Down's syndrome between 17 and 22 GW. Histochemical, immunocytochemical and ultrastructural examinations of microglial cells in frontal lobe, mesencephalon and cerebellum were carried out. A quantitative evaluation of developing microglia was performed in comparison with astroglial cells by counting the mean number of cells per 1 mm2. The study indicated that microglial cells emerge at the same time in all structures under study, both in normal fetuses and in those with Down's syndrome. It was also found that ameboid microglia (AM) and ramified microglia (RM) emerge at the same time and show the same morphological structure in both groups of fetuses. It was revealed that in the CNS of fetuses with Down's syndrome, the number of ramified microglial cells increased significantly as compared with in normal fetuses. Astroglial cells outnumbered microglial cells in the normal fetal development. Due to the enhanced number of RM cells in the CNS of fetuses with Down's syndrome the quantitative difference between these cells obliterated, and microglial cells in the frontal lobe cortex even outnumbered astroglial cells.