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The body composition of 40 healthy elderly and 20 healthy young subjects was determined and compared. It was found that the age-related changes were more marked in females than in males. Total body water was decreased as a consequence of diminished lean body mass. Extracellular fluid volume remained unchanged, while plasma volume increased. Thus, the liquid components of lean body mass were redistributed between the intracellular and extracellular spaces. The elimination kinetics of isotopes were not significantly different between young and aged subjects, except the elimination of radiosulfate.

The binding of 125I-labelled anti-bovine serum albumin (BSA)-BSA immune complexes (IC), giving a final molar antibody to antigen ratio of 1:1, to monocytes isolated from 18 patients with systemic lupus erythematosus (SLE) and from 10 normal healthy donors was quantitatively investigated. The degradation of the bound IC by the same monocytes was kinetically determined at the same time. The assays were performed on monocyte monolayers. Scatchard plots at 4 degrees C demonstrated that monocytes from patients with active SLE expressed a mean Fc gamma receptor (FcR) number that was 22% higher than that of the controls, although this did not reach statistical significance. The FcR number of normal monocytes and the degradation rate of anti-BSA-BSA complexes by the same cells showed a positive correlation. At the same time, the digestion of anti-BSA-BSA complexes by monocytes of SLE patients with active disease was prolonged, despite their enhanced FcR-ligand binding. The dissociation of FcR-ligand binding and FcR-mediated degradation suggests that the IC degradation is controlled by altered biochemical mechanisms in the monocytes of SLE patients.