Studies of the Reticuloendothelial System (res). 3. Blockade of the Res in Man.

In a previous communication (1), we have presented data indicating that the phagocytic capacity of the reticuloendotheial system (RES) in man can be determined safely and effectively by measuring the rate of disappearance of various doses of radioisotopically labeled aggregated human serum albumin particles from the blood after intravenous injection. Subsequently we reported that in patients with pneumococcal pneumonia, typhoid fever, and pneumonic tularemia (2), the phagocytic capacity of the RES was increased as evidenced by an accelerated rate of clearance of the aggregated albumin (AA) from the blood. In contast, in both viral infections studied, dengue and sandfly fever (3), there was a temporary inhibition of the body's ability to clear aggregated albumin, a finding consistent with studies in experimental animals in which phagocytic ability was found to be inhibited by viral infections (4). The safety of the method has been further confirmed during studies of the relationship between RES phagocytic activity in man and endotoxin tolerance (5). To date, over 1,500 administrations have been made in over 300 individuals without untoward reactions of any type. Therefore, we extended the studies in an attempt to characterize in man the phenomenon of RES blockade, the latter being defined as retardation of the usual rate at which particulate matter is removed from the circulation (6). In the present study, we have utilized in man and dog a modification of the technique employed by Murray in studies of rats (7). The RES was blockaded by administering various types of particles, and the effectiveness of blockade was tested by the subsequent injection of tracer doses of similar or dissimilar particles.