Phagocytosis and lipofuscin accumulation in lymph node macrophages.

Lipofuscin is considered to be undigestible material present in secondary lysosomes. During histological and electron microscopical studies lipofuscin was observed in macrophages in popliteal lymph nodes in 3-6 month-old-male Wistar rats after occlusion of the afferent lymph flow to the lymph node. No pathological alterations were found in the lymph node after the operation. However, the number of macrophages was severely reduced. Simultaneously the number of secondary lysosomes increased in the remaining macrophages reaching a plateau 4 weeks after operation. At this time three quarters of the residual bodies already contained lipofuscin granules. In the following weeks almost all macrophages showed lipofuscin in increasing amounts. Macrophages in normal contralateral lymph nodes of the same rats rarely contained lipofuscin. The increased phagocytosis of the remaining macrophages thus preceded the appearance of lipofuscin. We suggest that lipofuscin results from an inadequate intralysosomal digestion.