Differential expression of PLVAP between paired HCC tissue and adjacent non-tumorous liver tissue. A: Differential expression of the PLVAP gene according to microarrays of 18 pairs of HCC and adjacent non-tumorous liver tissue. PN: paired non-tumorous liver; PHCC: paired HCC tissue. B: Relative quantities of PLVAP mRNA in the same 18 tissue pairs. One non-tumorous liver tissue sample was chosen as a reference control (relative quantitative expression = 1). C: Immunohistochemical (IHC) staining of PLVAP in four randomly selected HCC cases. IHC staining was performed using GY5 murine anti-human PLVAP monoclonal antibody. Endothelial cells lining blood vessels of HCC showed positive staining for PLVAP in brown color (arrows). IHC staining (panel C) showed that PLVAP was not expressed by the endothelial cells of hepatic central vein (C-II right panel), hepatic sinusoid (CI-IV right panels), and hepatic arterioles (portal tract) (C-III right panel) in the adjacent non-tumorouse liver tissues. The large empty space in the right panel of C-II was lumen of a hepatic central vein which showed absence of PLVAP expression in the lining endothelial cells. We also stained HCC sections including adjacent non-tumorous liver with anti-human CD34 monoclonal antibody. Endothelial cells of hepatic central vein and hepatic areteriole were stained positively for CD34 expression (data not shown). Liver sinusoidal endothelial cells did not express CD34 as expected.