Expression of eotaxin in YS at 10.5 dpc. Eotaxin mRNA was assessed by in situ hybridization using a sense probe (a) or antisense probe (b and c). The endothelium (arrows, c) and cells in the vessel lumen (arrowhead, c) are positive. Immunoperoxidase staining was performed with a control antibody (d), antieotaxin MoAb (e), or a MoAb to CD34 (f). The visceral layer of cells, the endothelium, and primitive blood cells express eotaxin (e). In (e), the arrows identify the edge of the visceral cell layer. Magnifications are 100× (d), 400× (a, c, and f), and 1,000× (b and e).