Cellular aging of the reticuloendothelial system.

The reticuloendothelial system (RES) consists of macrophages and other endocytic cells which contribute to natural resistance to disease agents. The RES has been implicated as being partly responsible for the observed age-related decrease in resistance to pathogenic microorganisms in man and experimental animals. It is largely unknown to what extent age-related deficiencies in specific functions of reticuloendothelial cells contribute to the decrease of RES functions. This study describes experiments focussed on Kupffer and endothelial cells of the liver which represent a major part of the RES and are primarily responsible for clearance of potentially harmful substances from the circulation. The age-related changes in the clearance of a RES test colloid (heat-aggregated colloidal albumin (CA)) and of E. coli endotoxin were investigated using female BN/BiRij rats of various age groups. With CA, studies were performed on the plasma clearance and on the endocytic capacity of whole liver and of Kupffer and endothelial cells in vivo, as well as on the kinetics of endocytosis by Kupffer cells in culture. The results showed that the plasma disappearance of endotoxin was significantly prolonged in rats of 24 and 36 months resulting in an increase in half-life of about 50% as compared to young rats. The plasma clearance of CA, the uptake by the liver and the endocytosis by endothelial cells were unchanged with age. In contrast, an age-related decrease in endocytic capacity was observed in Kupffer cells in vivo and in Kupffer cells which were isolated from rats of various ages and maintained in culture.(ABSTRACT TRUNCATED AT 250 WORDS)