Role of Hofbauer Cells in Vasculogenesis of Chorionic Villi: Comparative Study in Normal Placentas, Complete Hydatidiform Moles, and Chorangioma
J-H Jo, JE Hwang, BH Park, K-R Kim. University of Ulsan College of Medicine, Seoul, Republic of Korea
Background: The circulatory function of the placenta appears at an early stage of placental development. The process of vasculogenesis in the chorionic villi involves the de novo differentiation of pluripotent mesenchymal cells to hemangiogenic stem cells (CD31 reactive) to angiogenic cell cords, and then the formation of mature blood vessels. Signals that regulate the vasculogenesis include complex processes with a number of factors involved, and the main regulator for angiogenesis is known to be the vascular endothelial growth factor (VEGF) family. It has recently been shown that Hofbauer cells (HCs) express high levels of VEGF mRNA, thereby indicating their involvement in vasculogenesis. However, we observed that CD31 reactive primitive stromal cells and angiogenic cell cords appeared prior to the appearance of HCs, thus raising the suspicion of their role in vasculogenesis.
Design: To investigate the role of HC in the vasculogenesis of chorionic villi, we compared the timing of the appearance and number of HCs in the villous stroma along with maturation of stromal blood vessels in 67 normal early placentas (weeks 4-11), 77 complete hydatidiform moles (CHMs, weeks 4-13), and 23 chorangiomas, using immunohistochemical stainings for CD68 (for Hofbauer cells) and CD31 (mature and immature blood vessels).
Results: In normal placentas, HCs began to appear during weeks 6-7, when angiogenic cell cords had been already formed. The number of HCs gradually increased after weeks 7-8 as the blood vessels matured and formed distinct lumen and hematopoietic cells. In 77 early CHMs in which the maturation of blood vessels was delayed or arrested, HCs were significantly decreased compared to normal placentas of the same gestational weeks; 45% (n=35) did not have HCs at all, 45% had few cells only in a few villi, and 9% (n=7) had them in multifocal villi (confined to 5-10 villi), but none of the CHMs had diffuse distribution of HCs as found in normal villi. The number of HCs within chorangioma was higher than in the adjacent normal villi, however, the amount seems to depend on the cellularity of chorangiomas; cellular and immature angiomatous types had more HCs compared to the mature angiomatous type.
Conclusions: HCs appear to be closely involved in the vasculogenesis of villous stroma, however, they may have a role in the vascular maturation rather than in the initiation of or commitment of pluripotent mesenchymal cells to the angiogenic cell cords.
Tuesday, March 10, 2009 1:00 PM
Poster Session IV # 155, Tuesday Afternoon