Effect of protein restriction on macrophage phagocytic capacity in young mice.

C57BL/6J male mice were fed ad libitum either a 6% (low) or 25% (control) protein diet for 2 to 6 weeks. At periods of 2, 3, 5 or 6 weeks following initiation of the feeding protocol thioglycollate-elicited peritoneal macrophages were assayed for Fc receptor-mediated phagocytic capability with IgG-coated sheep red blood cells (SRBC). Binding via this receptor (as monitored at 2 degrees C) was not affected by the protein restriction throughout the study. Ingestion of prebound IgG-SRBC was initially suppressed (2 weeks on diet) in macrophages from animals fed low protein but rose to a level significantly higher than similarly treated control animals after 5 weeks on the diet. At 3 and 6 weeks macrophages from control and low protein-fed animals exhibited no differences in ingestion capability. Overall phagocytosis (no prebinding of IgG-SRBC) was similar in trend to the data observed for ingestion. The data indicate both an altered response to phagocytosis with the low protein diet and the importance of quantitating the relationship between the duration of the nutritional insult and the parameter being measured.