TPO mRNA expression assessed by in situ hybridization on human liver sections. Liver sections of a patient with normal platelet counts (A and B) and a patient with ITP (C), probed with TPO cDNA probe. Strong signal development in hepatocytes but negative staining in endothelial cells (En) and interstitial cells (Int). Patchy signal distribution around portal tract (PTr). Liver section (D) from an individual with normal platelet count probed with plasmid vector pBR322 as a negative control. Original magnification: (A) ×108; (B and C) ×396; (D) ×240.