HLA-G5 is the HLA-G isoform present in erythroid cells from fetal liver. (A) Identification of HLA-G5 transcript in liver from 6-week (6w) and 7-week (7w) fetuses was determined by RT-PCR analysis and subsequent hybridizations. Specific amplification of soluble HLA-G was conducted by using forward primer CP5 and G.2734 primer sets. HLA-G products were detected by using either the G.R probe (specific for exon 2 encoding the α1 extracellular domain), the G.526 probe (specific for exon 3 encoding the α2 domain), or the G.647 probe (specific for exon 4 encoding the α3 domain). β-Actin products were amplified in the same reaction and were detected by using aβ-actin probe. Trophoblast villi from the same fetus and decidua from the corresponding mother were used as positive and negative controls of HLA-G gene transcription, respectively. (B) Identification of the 37-kDa HLA-G5 isoform was determined by running 1/25 of the total proteins extracted from 2 fetal livers of 9 weeks (9w) and 12 weeks (12w) on a 12% SDS-PAGE (polyacrylamide gel electrophoresis) gel followed by immunoblotting with the 5A6G7 mAb. The M8-HLA-G5 or M8-pcDNA transfectants were used as HLA-G5–positive and –negative controls, respectively. (C) Hematoxylin Eosin-Safran (HES) coloration of a paraffin-embedded 32-day embryo section (left) localizes the region of the liver for which higher magnifications of the same liver region stained with antibodies to CD34, HLA-G5, CD45, and CD71 are represented (right panel). HLA-G5 is detected in the erythroid cells which originate from the YS and are present in the lumen of sinusoids (embryo capillaries). The CD34 is positive in endothelial cells. Left panel is shown at × 20 original magnification; right panels are shown at × 400.