Loss of TSP-1 in platelets leads to accelerated tumor growth and increased tumor angiogenesis. (A) Lewis lung tumor cells were inoculated in the flank, and tumor growth was measured by calipers at the indicated days in lethally irradiated Tsp-1^−/− mice transplanted with either Tsp-1^−/− bone marrow (green line; n = 5) or wild-type bone marrow (red line; n = 5). (B) Microvessel density (MVD) per high-power field (hpf) was quantified in equivalent volume tumors harvested from Tsp-1^−/− mice transplanted with wild-type or Tsp-1^−/− bone marrow (P < .005). (C) Bioluminescence images of intraperitoneal tumors in mice after injections of platelet buffer alone, 10⁹ wild-type, or Tsp-1^−/− platelets. (D) CD31 and TSP-1 immunofluorescence of tumors harvested from mice injected with platelet buffer alone (control), wild-type platelets, or Tsp-1^−/− platelets. Tumors were immunostained with an antibody against CD31 (left panels) to detect endothelial cells and for TSP-1 (right panels). Bar represents 20 μm. (E) MVD/hpf was quantified by CD31 immunostaining of intraperitoneal tumors harvested from mice injected with platelet buffer, wild-type platelets, or Tsp-1^−/− platelets (P < .005).