Immunohistochemical detection of the tumor vasculature in representative Burkitt tumors treated with MBP or MBP-calreticulin. Paraffin-embedded tumor sections were stained with mouse anti-alpha smooth muscle actin monoclonal antibody and counterstained with hematoxylin. (A) Representative tumor tissue from a mouse treated with MBP alone. (B) Representative tumor tissue from mouse treated with MBP-calreticulin (original magnification ×20).