Invasive trophoblasts lining maternal decidual blood vessels express CXCL12. Immunohistochemistry on paraformaldehyde-fixed serial decidua tissue sections (12 weeks; 6 μ). Staining with anti–von Willebrand factor polyclonal antibody (A-B) and CXCL12 (C-D) of decidual blood vessels undergoing endovascular invasion by trophoblasts. Arrows indicate endothelial cells; **, invasive trophoblasts. The magnification for each panel is indicated in the lower right corner.