Representative immunohistochemistry for COX-2 in washed platelets from ET patients and healthy subjects. Immunoperoxidase of washed platelets from a control subject (A) and a patient (B), stained for COX-2 revealed with diaminobenzidine chromogen; platelets were lightly counterstained with eosin. Examples of COX-2-positive platelets are indicated by. In each panel a COX-2-positive leukocyte is visible and indicated by the asterisk as intensity staining control. Samples were analyzed by light microscopy using an Axioskop microscope (Zeiss), with an objective lens type Plan-neo Fluar (Zeiss) at a numerical aperture of 1.30, in oil. Original magnification, ×1000. Images were photographed by a CoolPix 950 digital camera (Nikon).