This study was conducted to compare the immunohistochemical and morphometric characteristics of blood vessels in brain metastasis with blood vessels of the adjacent uninvolved brain tissue. This is based on the hypothesis that new vessels formed in the tumor express antigens that are not expressed in blood vessels of the adult brain parenchyma. Thus, a panel of antibodies known to react with mouse endothelial cells at various stages of differentiation or stimulation was tested on frozen sections of experimental brain metastasis. Intratumoral microvessel density which has been reported to reflect the intensity of tumor angiogenesis was inapplicable to experimental brain metastasis therefore other parameters were measured.

Brain metastasis was produced in nude mice following intracarotid injection of tumor cells. Three human tumors and three murine tumors were injected into the carotid artery of nude mice. The animals were sacrificed when they were moribund, the brains were embedded in OCT and frozen in liquid nitrogen. Some animals were injected with bromodeoxyuridine (BrdU) 1 h before they were necropsied. Immunohistochemistry was performed using antibodies directed to the following antigens: CD31, CD34, MECA-32, endoglin, ICAM-1, ICAM-2, and BrdU. Antibodies to leukocyte antigens, F4/80 and CD3 were also tested to determine the amount of host cells infiltrating the tumors. SEM of immunogold labeled preparations determined the cellular localization of some antigens.