Protección del epitelio respiratorio frente a la infección y el daño celular por lípidos y proteínas del fluido alveolar

Resumo

The respiratory system is needed to obtain the oxygen required for cellular metabolism and to expel the carbon dioxide produced as a waste in this process. The gas exchange takes place in the alveoli, where oxygen and carbon dioxide diffuse between the alveolar epithelium and erythrocytes of the bloodstream. To carry out this function, the alveolar epithelium is the largest surface of the body exposed to the external environment and it is in contact with a variety of agents, such as pathogens, particles and other toxic substances (1). To control these potential harmful agents while maintaining tissue homeostasis that allows gas exchange, an effective immune system is required. The immune system also may limit excessive inflammation that can lead to tissue damage. The innate immune system is in charge of controlling these functions (2). In the alveoli, this system consists of a humoral component: antimicrobial peptides and proteins as well as lipids from the alveolar fluid; and a cellular component: alveolar macrophages, dendritic cells, and epithelial cells (3).The alveolar fluid contains the pulmonary surfactant, which is a lipoprotein complex that covers the alveolar epithelium and is essential to reduce surface tensionat the air-liquid interface, preventing alveolar collapse and allowing gas exchange. In addition, pulmonary surfactant is an integral component of the lung's innate immune system, controlling inflammation and preventing microbial infections (4,5). These two essential functions (decreased surface tension and host defense) depend on the complexity of their components, coordinating both functions so that defense mechanisms do not interfere with tensioactive properties (5)...