Figure 1. Immunohistochemical staining of first trimester placenta serial paraffin sections at the 11^th week of pregnancy.

Villous chorion (A, B) and umbilical cord vessels (C, D) stained for IDO1 (A, C) and for the endothelial marker CD34 (B, D); bigger vessels located more to the center of the villi are indicated by arrowheads, capillaries forming a network beneath the trophoblastic double layer stain positive for IDO1. The scale bar represents 100 µm.