DISTRIBUTION OF IMMUNE EFFECTOR-CELLS WITHIN AN EXPERIMENTAL OSTEOSARCOMA OF THE NUDE RAT

In vivo studies on osteosarcoma are limited by the relative low incide nce of this tumor in man. Therefore, there is a high dependence on a r eliable experimental tumor model. In previous studies, a transplantabl e osteosarcoma of the athymic nude rat was established. In the present study the content and pattern of distribution of immune effector cell s within this osteosarcoma were investigated by immunohistochemistry, and were related to histomorphologic findings. The absence of T-like c ells within the tumor of 1- to 2-month-old athymic nude rats was shown using the T-lymphocyte-specific monoclonal antibody OX-19. In contras t, OX-6-positive cells, representing B lymphocytes and macrophages, we re distributed throughout the whole tumor with a discrete accumulation at the borderline between the peripheral proliferative tumor tissue a nd the central necrotic area. Using the macrophage-specific monoclonal antibody ED 1 we found the accumulation of mononuclear cells to consi st mainly of macrophages. The distribution of these macrophages was cl osely related to histomorphologic tumor characteristics: the major pro portion was found in the proliferative peripheral part of the tumor wi th highest macrophage content at the border to the central necrosis. A s the measurement of tumor necrosis in osteosarcoma plays an important role in the judgement of therapeutic response, this distinct delimita tion of tumor necrosis by macrophages could be helpful in the evaluati on of therapeutic effects. Whether the demonstrated accumulation of B lymphocytes and macrophages is a secondary effect in the course of the removal of necrotic tissue, or a primary T-lymphocyte-independent tum or defense should be the aim of further studies.