Radiation Effect on the Barrier Function of the Lymph Node

There is definite evidence both that the lymph node is an effective lymph filter (4, 12) and that its lymphatic tissues are rapidly depleted following irradiation (2, 3, 9). It is of obvious interest to evaluate the effect of radiation on the barrier function of the lymph node. Clinical radiation therapy often encompasses regional lymph nodes in order to eradicate a neoplastic process. Theoretically it would be disadvantageous if, following such treatment, the barrier function of the lymph node were greatly compromised. In our experiments we studied the filtering efficiency of irradiated popliteal lymph nodes of the dog. The evaluation was based on microradiographs of midplane sections of the lymph node which had been challenged, before removal, by subcutaneous administration of Thorotrast. The quantity and the distribution of the Thorotrast particles provided information concerning the barrier function of these nodes. Review Of Literature In 18, 58 Virchow (11) stated that, in the lymph node, “the elements lie crowded together like a charcoal filter.” This basic mechanical concept of filtration has been subsequently greatly expanded. Lymph nodes were considered not only filters in the path of the lymph but also effective agents against harmful elements in the blood circulation. Numerous experimental studies have shown that lymph nodes are effective filters of different particles and cells (4, 12). We have shown (10) that if the popliteal lymph node of the dog is perfused by a small number of autologous red cells the primary filtering mechanism is phagocytosis, which takes place in the sinusoids. If the number of cells increases, the lymph node also behaves like a mechanical settling chamber. The effects of irradiation on the lymph node have been intensively studied since 1904, when Heineke (6) described the massive depletion of lymphocytic tissues after whole-body irradiation. While Heineke pointed out the difference in the relative radiosensitivity between the lymphocytes and the reticular elements, subsequent studies have confirmed and more fully described this difference. De Bruyn (2, 3) stated that, if 800 R total-body irradiation is given to rabbits, the lymphocytes are very radiosensitive but the reticular cells and macrophages are unaltered. Barrow, Tullis, and Chambers (1) showed that following total-body irradiation of rabbits (800 R) there is no interference with the uptake of colloidal gold in the reticuloendothelial cells. Materials And Methods Ten apparently healthy young mongrels weighing approximately 10 kg each were studied. Radiation All animals received local irradiation of the left popliteal region under Pentothal anesthesia. A circular field 7 cm in diameter was used. Physical factors were 250 kV, 1 mm Cu h.v.l., at 45 cm target-skin distance. In all experiments the right popliteal node served as the control.