Vascular effects and NK-cell recruitment in experimental Burkitt tumors treated locally with IL-12. (A) Effects of local diluent (FB) or IL-12 inoculation (200 ng/mouse/d, 7 d/wk) on the growth of Burkitt tumors established subcutaneously in nude mice. The results reflect mean (±SD) tumor sizes of 4 animals/group. (B) Gross morphology of a representative Burkitt tumor treated locally with IL-12 for 34 days (no magnification). (C) Microscopic morphology of a representative Burkitt tumor treated locally with IL-12 for 34 days depicting vascular pathology (original magnification ×40). (D, E) Immunohistochemical detection of NK cells by the B220 monoclonal antibody in representative Burkitt tumors treated locally with IL-12 depicting positive cell staining surrounding a capillary vessel with discontinuous endothelium (D, original magnification ×40), and positive cell staining surrounding a small arteriole (E, original magnification ×40).