What happens if protein is deposited in the alveoli? How to treat it?

Author: Fang Baomin, Chief Physician, Beijing Hospital

Reviewer: Zhi Xiuyi, Chief Physician, Xuanwu Hospital, Capital Medical University

The alveoli are the main site of gas exchange in the lungs and are also the functional units of the lungs. The inhaled oxygen diffuses from the alveoli to the blood. After entering the blood, the venous blood becomes oxygen-rich arterial blood and is transported to all parts of the body through the blood circulation. At the same time, the carbon dioxide in the venous blood diffuses into the alveoli and is finally exhaled through the respiratory tract.

Figure 1 Original copyright image, no permission to reprint

Today we will learn about a disease related to alveoli, called alveolar proteinosis.

Pulmonary alveolar proteinosis is mainly caused by the accumulation of a large amount of surfactant in the alveoli and the abnormal phagocytic function of macrophages in the body, which leads to the obstruction or abnormality of the clearance of surfactant by alveolar macrophages.

Under normal circumstances, lung tissue produces a surfactant that is mainly used to maintain alveolar tension. This substance is in a dynamic equilibrium process in the body. The body is constantly producing it and clearing it at the same time, mainly relying on alveolar macrophages to phagocytize and clear it. When there is a problem with the function of alveolar macrophages, the clearance of alveolar surfactant is impaired, and the surfactant will be deposited in the alveolar cavity, leading to pulmonary alveolar proteinosis.

There are two causes of pulmonary alveolar proteinosis: internal and external. Most of them are external. Currently, there are three possible mechanisms of disease. First, the body produces anti-GM-CSF antibodies. Second, genetic abnormalities, that is, hereditary pulmonary alveolar proteinosis. Third, certain diseases, such as blood system diseases, lead to alveolar macrophage dysfunction. The most common cause is the production of anti-GM-CSF antibodies.

If there is protein deposition in the alveoli, the alveolar ventilation function will be affected, and gas exchange will not be possible, which will manifest as dyspnea, cough, cyanosis, etc. In the early stage, you will feel chest tightness and shortness of breath during strenuous activities, and feel that you are not getting enough air. As the disease becomes more and more serious, the degree of hypoxia becomes more and more obvious, and dyspnea will gradually worsen. In the late stage, even in a quiet state, it will manifest as hypoxemia and dyspnea.

If pulmonary alveolar proteinosis is suspected, the most convenient and reliable method is to perform bronchoscopic alveolar lavage. After the bronchoscope enters the lungs, it injects saline into the lungs, which then absorbs the saline back out. The saline becomes turbid, and in this case it is very likely pulmonary alveolar proteinosis. Of course, testing the reabsorbed saline can confirm the diagnosis.

Figure 2 Original copyright image, no permission to reprint

In addition, lung biopsy can be performed through bronchoscopy. Lung tissue biopsy can reveal the deposition of alveolar surfactant in the alveolar cavity and this characteristic change can help to confirm the diagnosis.

A small number of patients with pulmonary alveolar proteinosis can recover on their own, but the condition of most patients will become more and more serious over time. If left untreated, breathing difficulties will become more and more obvious, hypoxia will become more and more severe, and finally lead to respiratory failure, which is life-threatening.

The treatment method for pulmonary alveolar proteinosis is mainly selected according to the cause. Hereditary pulmonary alveolar proteinosis is caused by genetic abnormalities. The current treatment mainly involves alveolar lavage. Normal saline is poured into the lungs every once in a while to wash out the surfactant, which can relieve the symptoms. However, after a period of time, the surfactant will be deposited again, and alveolar lavage must be done again.

If it is caused by other diseases, such as blood system diseases and occupational dust exposure, the cause should be removed first and the primary disease should be treated, then secondary pulmonary alveolar proteinosis can be improved or cured.

Primary pulmonary alveolar proteinosis is caused by the body's production of anti-GM-CSF antibodies. There are several treatment options available. The first choice is alveolar lavage, followed by inhalation of GM-CSF cytokines, which are mainly used to maintain the function of alveolar macrophages and restore the function of alveolar macrophages to achieve the purpose of treatment. For some very serious patients, plasma exchange and the use of high-dose drugs produced by anti-cellular antibodies can be considered. These methods are used less frequently, mainly alveolar lavage, followed by inhalation of GM-CSF cytokines, which are currently the main treatment options for primary pulmonary alveolar proteinosis.