Influence of Dietary Protein on Complement, Properdin, and Hemolysin in Adult Protein-depleted Rats

Three immunoproteins were measured in normal and in protein-depleted adult male rats and in animals which had been depleted of protein for 4 weeks and then repleted for 2 or 3 weeks with a diet containing 9 or 18% casein, 9 or 18% egg protein, 9% soy α-protein, 9% soy α-protein plus 0.25% methionine, 9% wheat gluten, 9% wheat gluten plus 0.35% lysine, or with stock ration. One milliliter 2% sheep erythrocytes was injected 2 weeks before the end of the experiment, and antibody titer was measured at intervals thereafter. Complement and properdin were titrated in serum obtained at autopsy. Titers of antibody, but not of complement or properdin, decreased significantly in the first 6 weeks of protein depletion. Weight gain and repletion of nitrogen in liver and in serum were rapid in animals repleted with stock ration, 18% egg protein or 18% casein, and slowest in those fed 9% soy α-protein or 9% wheat gluten. In contrast, properdin and antibody titers were inversely related to rate of gain and also to the total amount of sulfur amino acids in the diet.