Biliary immunoglobulins in protein-energy malnourished rats

The effect of protein-energy malnutrition on biliary immunoglobulins was investigated in rats fed isocaloric diets containing 0.5%, 5%, and 18% casein, respectively. Growth was severely retarded in rats fed 0.5% casein diet and moderately in rats fed 5% casein diet, and these groups had decreases in serum albumin and total protein levels. Since the energy intake was low in rats fed protein-insufficient diets, the nutritional status was defined not as protein malnutrition but protein-energy malnutrition. Depression of systemic immune functions in protein-energy malnourished rats were demonstrated by serum IgG and IgA levels, and antibody responses to dinitrophenylated bovine gamma globulin, a T-cell dependent antigen. The depressed systemic immune functions observed in those rats were suggested to be caused by thymic atrophy. IgA levels in bile were much higher in all groups than IgG levels. IgG levels decreased in rats fed 0.5% casein diet but not in rats fed 5% casein diet, while IgA levels decreased in rats fed 5% and 0.5% casein diet relating to casein levels. The ratios of IgA to IgG in bile also decreased in rats fed protein-insufficient diets. By sucrose density gradient centrifugation secretory IgA levels in bile were shown to decrease in rats fed 0.5% casein diet, suggesting that the secretion of IgA by hepatic parenchymal cells is depressed in the protein-energy malnourished rats.