Alteration of the respiratory burst and phagocytosis of macrophages under protein malnutrition.

To understand the role of macrophages in impaired host defense under protein malnutrition (PM), we examined the activities of the respiratory burst and phagocytosis of resident peritoneal macrophages from weaning female mice fed 5% casein or 5% soy protein isolate (SPI) diet for 14 days. Resident macrophages from the low-protein diet groups released larger amounts of superoxide anion (O2-) after stimulation by phorbol 12-myristate 13-acetate (PMA) or opsonized zymosan than those from the 20% casein and 20% SPI diet groups. Activation of macrophages from protein-deficient mice in vitro with lipopolysaccharide (LPS) or macrophage colony-stimulating factor (M-CSF) under LPS-free conditions did not further enhance O2- production. In spite of the increased O2- production with opsonized zymosan, macrophages from protein-deficient mice did not show any acceleration of phagocytosis of Candida albicans in the presence of normal serum. Our results confirm that the phagocytic function of macrophages is susceptible to PM, and suggest that functional alterations of macrophages may be involved in the failure of development of a specific immune response under PM. Furthermore, the enhanced production of oxygen intermediates by macrophages may augment tissue damage under PM.