Immunohistochemical peroxidase staining of CD44 on normal tissue and RCC associated EC. Frozen tissue sections of human umbilical vein (A and B), normal renal tissue (C and D), and RCC (E and F ) were stained for EC-marker EN4 (A, C, and E) and CD44 (NKI-P1 antibody, B, D, and F ). The arrows in (A and B) identify the EC layer. In (C and D) the arrows identify the glomeruli and the arrowheads mark the EC in the larger vessels. From the RCC sections one vessel is magnified (insets). Bars represent 50 μm, in (A) for (A and B), in (C) for (C through F ), insets same magnitude.