HLA-G5, a soluble glycoprotein, is the only isoform that is expressed in all subpopulations of trophoblast cells, including those in the villous (left), those in the column, and those forming the trophoblastic shell that attaches to the decidua. All tested isoforms appear to be expressed in the trophoblastic shell and to be maintained as the cells progress through the interstitum of the decidua and invade the spiral arteries.