Enhanced phagocytic activity of lymph node macrophages after intranodular injection of autologous red blood cells.

Rabbits were killed 1 h to 12 days after injection of washed autologous red blood cells (RBC) into the paratracheal cervical lymph nodes. Microscopic, electron-microscopic, and histochemical techniques were used to study the time-dependent ingestion and digestion capacity of phagocytes in the lymph nodes. One hour after intranodular injection of RBC, a greater portion of the target cells had already attached to the surface of and were partly ingested by sinusoidal phagocytes in the marginal zone and medulla. After 6 h, degradation of erythrocyte hemoglobin into hemosiderin could be demonstrated in a few of the cells. After 9 days, erythrocytes, erythrophages, and hemosiderophages had disappeared and could no longer be observed in the lymph nodes. Comparative morphological and histochemical studies showed these phagocytes to be macrophages. The possibility of an opsonizing or a humoral factor in lymph serum which stimulates phagocytosis was excluded in in vitro studies (peritoneal macrophages incubated with lymph serum and RBC) and the possibility of phagocytosis induced by a T-cell-macrophage interaction, was excluded in in vivo studies with athymic nude mice. Comparable enhanced phagocytic activity of lymph node macrophages could be observed in vitro after injection of RBC into isolated lymph nodes of rabbits. The finding presented here indicate that marginal zone and medullary macrophages are primarily activated and that they eliminate autologous RBC from the sinuses without any additional stimulus by mechanisms which have not yet been clarified.