Alveolar type II cell (ATII cell (or AT2 cell))

**Alveolar type II cell** (*ATII cell*, also called "Type II pneumocyte") is a specialized epithelial cell found in the alveoli of the lung. It is cuboidal, comprises about 60% of alveolar epithelial cells by number (but covers only ~5% of surface area), and is responsible for the synthesis, storage (in lamellar bodies), and secretion of pulmonary surfactant, which is essential for reducing alveolar surface tension and preventing collapse during exhalation[1][2][3][4][5]. ATII cells also regulate alveolar fluid and ion balance, express innate immune mediators, participate in local immune responses (including expressing MHC class II), and serve as progenitor/stem cells for alveolar type I cells, playing a critical role in epithelial repair and regeneration after lung injury[2][4][5][6]. Dysfunction or loss of ATII cells is implicated in multiple lung disorders, including acute and chronic lung injuries, fibrosis, cancer (e.g., adenocarcinoma), and COVID-19-related lung disease[2][4][6]. **Note:** "Alveolar type II cell" is a **cell type**, not a canonical molecular target such as a receptor or enzyme and thus is generally not considered a direct "therapeutic target" in the traditional sense (e.g., drugs do not bind to it as to a receptor). However, its dysfunction is involved in several diseases, and its specific markers (notably surfactant protein C) can be used as biomarkers in research and diagnostics[3][4]. Targets for drug development are more often focused on receptors, channels, or pathways within these cells rather than the cell type itself. Therefore, this entity is **not a molecular/druggable target by standard classification**[1][2][3][4][5][6].

Other names

Alveolar type II pneumocyteATII cellAT2 cellType II alveolar cellType II pneumocyte