As in previous studies, we have shown that AM from patients with pulmonary alveolar proteinosis have decreased phagocytic ability in vitro. The acridine orange assay allows for a direct quantitative assessment of phagocytosis, and the present data show no differences in the proportion of macrophages from pulmonary alveolar proteinosis, compared with normal human AM, ingesting yeast; but the total phagocytic activity is decreased because macrophages from pulmonary alveolar proteinosis, on the average, ingest fewer yeast cells. Golde and co-workers did not find this type of abnormality with a 60-minute challenge, but Harris and Nugent and Pesanti did when AM were challenged with bacteria for two or more hours. At the time of the phagocytosis assays, the AM from patients with pulmonary alveolar proteinosis had been in cell culture and removed from the alveolar-filling material obtained by lavage; therefore, the decreased phagocytic activity was a property of the AM themselves, rather than a suppression of function dependent on continuous exposure to alveolar-filling material. Alveolar macrophages from one patient with pulmonary alveolar proteinosis were examined after seven days in culture, and decreased phagocytic activity persisted at that time. The phagocytic process is an energy-dependent event and can be affected by metabolic inhibitors, surface-active agents, certain drugs that may bind to sulfhydryl groups, and chelators of divalent cations. Various components of the lavage material might affect phagocytosis by AM in some similar fashion. Breath-taking information about medicine are located on the website of Canadian Neighbor Pharmacy.
A new observation of this study is that AM from each of the three patients whom we studied had a defect of phagolysosome fusion as measured by transfer of lysosomal contents to phagosomes. In addition, defective phagolysosome fusion was induced in AM from normal human volunteers and rats when the AM were incubated with a cell-free fraction of alveolar material (PJ isolated from lavage of these patients. The P1 fraction was granular and amorphous when viewed by light microscopy and appeared to be the predominant component of the alveolar-filling material seen on histologic examination of lung biopsies from the patients with pulmonary alveolar proteinosis. This demonstration that normal human AM can become abnormal after exposure to material from alveolar proteinosis supports the idea put forward by Golde and coworkers that AM become abnormal in pulmonary alveolar proteinosis after they enter the alveolar spaces.
Because the abnormality in phagolysosome fusion correlates with morphologic changes in AM, specifically the presence of many large intracellular inclusions that probably represent secondary lysosomes, it might be considered that functional changes could be a consequence of the morphologic change. One might speculate that the large number and size of cytoplasmic inclusions in these AM might restrict the movement in lysosomes in these cells and decrease phagolysosome fusion. Although it is doubtful that their macrophages were as “bloated” as the AM from patients with pulmonary alveolar proteinosis, Kielian and Cohn reported that the rate of phagolysosome fusion was unaffected either by prior uptake of digestible or nondigestible substances or by the number or size of lysosomes. From data presently available, we cannot determine whether the decrease in phagolysosome fusion is simply a mechanical problem with restriction of phagosomal and lysosomal movement or whether phagolysosome fusion is depressed by another mechanism by factors in the lavage material. Components in the alveolar-filling material of the patients might inhibit phagolysosome fusion in a manner similar to that of known inhibitors such as weak bases like ammonium chloride or polyanions, or certain mycobacterial products such as sulfatides 1 and 3.
One consideration would be the possible influence of cigarette smoking on the findings in the two patients with pulmonary alveolar proteinosis who were exsmokers. We have previously shown that chronic inhalation of cigarette smoke may decrease phagolysosome fusion in AM from experimental animals; however, the observed defect in the patient with pulmonary alveolar proteinosis who was a nonsmoker and the ability to produce a defect in phagolysosome fusion in AM from normal nonsmokers by exposing the cells to the lavage material from the patients with pulmonary alveolar proteinosis that smoking alone does not account for the abnormality observed in AM from these patients.
The present study and the reports previously cited indicate that components of the alveolar-filling material from patients with pulmonary alveolar proteinosis have the potential to depress the phagocytic process in three ways: (1) by inhibiting ingestion of phagocytic particles; (2) by decreasing the rate of ingestion; and (3) by decreasing phagolysosome fusion. These data further support the idea that defective AM function in pulmonary alveolar proteinosis is caused by “toxic” components of the alveolar-filling material that characterizes this disorder and that the defective handling of phagocytized microorganisms by resident macrophages could affect pulmonary defense mechanisms. Our finding that phagolysosome fusion in AM is decreased adds to our understanding of the susceptibility of these patients to infections with less common pulmonary pathogens, such as Nocardia, Mucor, His-toplasma, and Cryptococcus, that survive intracellularly in macrophages when phagolysosome fusion is inhibited.