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Changes of alveolar macrophages in protein-deficient rats
Abstract:
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.
Insights
Protein malnutrition significantly reduces the number of alveolar macrophages (AM) in rats. While AM phagocytosis of some particles remains unchanged, their ability to engulf opsonized red blood cells is altered, impacting lung defense.
Area of Science:
- Immunology
- Nutrition Science
- Cell Biology
Background:
- Dietary protein is crucial for immune function.
- Alveolar macrophages (AM) are key immune cells in the lung.
- Protein malnutrition can impair host defense mechanisms.
Purpose of the Study:
- To investigate the effects of protein malnutrition on rat alveolar macrophages (AM).
- To assess functional changes in AM phagocytosis and response to macrophage-activating factor (MAF).
Main Methods:
- Female F344 rats were fed a 5% casein diet for 7 weeks to induce protein malnutrition.
- Alveolar macrophages (AM) were isolated via broncho-pulmonary lavage.
- Phagocytosis assays (latex beads, yeast, opsonized sheep red blood cells) and MAF response were measured.
- Ultrastructural analysis of AM surface microvilli was performed.
Main Results:
- Protein malnutrition reduced AM numbers but maintained phagocytosis of latex beads and yeast cells.
- Phagocytosis of opsonized sheep red blood cells (SRBC) increased, but MAF responsiveness was lost.
- AM exhibited abundant surface microvilli, which decreased after SRBC ingestion.
Conclusions:
- Dietary protein deficiency impacts AM number and function.
- Altered AM phagocytosis and MAF response in malnutrition compromise lung host defense.
- Changes in AM ultrastructure correlate with impaired immune function.