Distribution of immune effector cells within an experimental osteosarcoma of the nude rat

In vivo studies on osteosarcoma are limited by the relative low incidence of this tumor in man. Therefore, there is a high dependence on a reliable experimental tumor model. In previous studies, a transplantable osteosarcoma of the athymic nude rat was established. In the present study the content and pattern of distribution of immune effector cells within this osteosarcoma were investigated by immunohistochemistry, and were related to histomorphologic findings. The absence of T-like cells within the tumor of 1- to 2-month-old athymic nude rats was shown using the T-lymphocyte-specific monoclonal antibody OX-19. In contrast, OX-6-positive cells, representing B lymphocytes and macrophages, were distributed throughout the whole tumor with a discrete accumulation at the borderline between the peripheral proliferative tumor tissue and the central necrotic area. Using the macrophage-specific monoclonal antibody ED1 we found the accumulation of mononuclear cells to consist mainly of macrophages. The distribution of these macrophages was closely related to histomorphologic tumor characteristics: the major proportion was found in the proliferative peripheral part of the tumor with highest macrophage content at the border to the central necrosis. As the measurement of tumor necrosis in osteosarcoma plays an important role in the judgement of therapeutic response, this distinct delimitation of tumor necrosis by macrophages could be helpful in the evaluation of therapeutic effects.(ABSTRACT TRUNCATED AT 250 WORDS)