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Pulmonary alveolar proteinosis. Further evaluation of abnormal alveolar macrophages
Abstract:
To investigate the function of alveolar macrophages (AM) and the mechanisms of impairment in pulmonary alveolar proteinosis, we established in culture AM from three patients and from eight normal nonsmokers and assessed phagocytosis and phagolysosome fusion by the acridine orange assay with live yeast as the phagocytic challenge. Alveolar macrophages from the patients with pulmonary alveolar proteinosis ingested fewer yeasts per cell than did normal AM (mean +/- SE, 2.3 +/- 0.3 vs 3.3 +/- 0.2; p less than 0.05) and had decreased phagolysosome fusion (33 +/- 6 percent vs 64 +/- 1 percent; p less than 0.001). Alveolar macrophages from three normal subjects were incubated with cell-free fractions isolated by centrifugation of lavage fluid from the patients at 250 g (P1) or centrifugation of P1 supernatant at 20,000 g (P2). The P1 fraction did not decrease the number of AM ingesting yeast or the number of yeast cells ingested per cell, but the P2 fraction decreased both phagocytic indices. Conversely, phagolysosome fusion was depressed by the P1 fraction (48 +/- 3 percent vs 66 +/- 2 percent for untreated AM from the same subject; p less than 0.02) but not by the P2 fraction. Significant morphologic changes were noted in AM cocultured with both P1 and P2. Comparable concentrations of pooled P2 fractions from normal subjects did not decrease phagocytic indices in normal AM. These data confirm that AM in pulmonary alveolar proteinosis are dysfunctional, and, in particular, the finding of decreased phagolysosome fusion may be related to the high incidence of uncommon infections in these patients. We have shown that different fractions of alveolar filling material from patients with pulmonary alveolar proteinosis have unique effects on the phagocytic process in the normal AM, and the induced defects may be associated with apparent uptake of this material. These observations further support the hypothesis that in patients with pulmonary alveolar proteinosis, locally produced "toxic" substances may lead to impaired alveolar clearance and contribute to the pathogenesis of this disease.
Insights
Alveolar macrophages (AM) from patients with pulmonary alveolar proteinosis show impaired phagocytosis and phagolysosome fusion. Lavage fluid fractions from these patients further impair normal AM function, suggesting toxic substances contribute to disease pathogenesis.
Area of Science:
- Pulmonary Medicine
- Cell Biology
- Immunology
Background:
- Pulmonary alveolar proteinosis is characterized by the accumulation of surfactant-like material in alveoli.
- Alveolar macrophages (AM) play a crucial role in clearing alveolar debris and pathogens.
- Dysfunction of AM may contribute to the pathogenesis of pulmonary alveolar proteinosis and associated infections.
Purpose of the Study:
- To investigate the functional deficits of AM in patients with pulmonary alveolar proteinosis.
- To identify mechanisms underlying AM impairment in this condition.
- To explore the role of alveolar lavage fluid components in affecting AM function.
Main Methods:
- Cultured AM from patients and healthy controls were assessed for phagocytosis and phagolysosome fusion using live yeast and the acridine orange assay.
- Normal AM were incubated with cell-free fractions (P1 and P2) derived from the lavage fluid of patients.
- Morphological changes in AM were evaluated after co-culture with lavage fluid fractions.
Main Results:
- AM from patients exhibited significantly reduced yeast ingestion and phagolysosome fusion compared to normal AM.
- The P2 fraction of patient lavage fluid impaired both phagocytosis and phagolysosome fusion in normal AM.
- The P1 fraction of patient lavage fluid inhibited phagolysosome fusion in normal AM, with both fractions causing morphological changes.
- Lavage fluid fractions from normal subjects did not impair normal AM function.
Conclusions:
- AM in pulmonary alveolar proteinosis are indeed dysfunctional, particularly regarding phagolysosome fusion.
- Components within the alveolar lavage fluid of patients, possibly toxic substances, contribute to AM impairment.
- These findings support the hypothesis that impaired alveolar clearance due to locally produced toxic substances plays a role in the pathogenesis of pulmonary alveolar proteinosis.