Human spleen sections probed with TPO cDNA probe. Splenic sections of an individual with normal platelet count (A) and an individual with ITP (B and C). Faint, almost negative hybridization signal in the splenic cells, but clearly negative staining in the endothelial cells (En) and fibroblasts (Fb). Spleen section from patient with normal platelet count (D) probed with plasmid vector pBR322 as a negative control. The orange staining cells are erythroid cells (Ery) that do not show any positive signal development. Original magnification: (A and C) ×400; (B and D) ×240.