TSP-1 is not expressed by CLL cells. CLL cells in all cases tested for TSP-1 expression by immunohistochemistry were negative. In the left panel is a case of CLL with a field of TSP-1 negative lymphocytes. At the center of this field is an internal positive control, a megakaryocyte. The TSP-negativity of CLL cells was verified by flow cytometry. All 21 cases tested had results similar to the cases illustrated in the middle panel. HUVEC cells, which are known to express TSP-1, were positive by flow cytometry (right panel).