Changes of alveolar macrophages in protein-deficient rats.

Protein malnutrition was achieved by feeding female F344 rats a 5% casein diet for 7 weeks. At appropriate times, animals were killed and their alveolar macrophages (AM) were obtained by broncho-pulmonary lavage of the lung. Functional changes of AM were determined by measuring phagocytosis of latex beads, yeast cells or opsonized sheep red blood cells (SRBC) and the ability to respond to a macrophage-activating factor (MAF) such as lymphokines. After 3 weeks on a low casein diet, the number of AM was much lower than in rats on control diet, but the abilities of the AM to phagocytose latex and yeast cells were the same as those of controls. Phagocytosis of opsonized SRBC was higher than in control rats but could not be enhanced by in vitro treatment with MAF. The most striking ultrastructural feature of these AM was the abundance of finger-like microvilli on the cell surface before phagocytosis; after ingestion of SRBC into phagocytic vacuoles there were only a few short microvilli on the surface. These data suggest that dietary protein malnutrition affects the number and phagocytic functions of AM responsible for host defense in the lung.