AT2

At2 is an abbreviation used in multiple scientific contexts, most prominently in biology and medicine. The two principal meanings are alveolar type 2 cells in the lung and the angiotensin II receptor type 2. Outside of these fields, the designation may appear as a product name or model code, but there is no single universal definition.

Alveolar type 2 cells (often abbreviated AT2) are specialized epithelial cells located in the alveoli of the lungs. They produce and secrete pulmonary surfactant, a lipid-protein complex that reduces surface tension and prevents alveolar collapse. AT2 cells also store surfactant in lamellar bodies and act as progenitors for alveolar type 1 cells, helping to regenerate the alveolar epithelium after injury. Their molecular markers include surfactant proteins SFTPC, SFTPB, SFTPD, and the transporter ABCA3.

Angiotensin II receptor type 2 (AT2 receptor) is one of the two main receptors for angiotensin II, a peptide that influences vascular tone and fluid balance. The AT2 receptor is a G protein–coupled receptor with a distribution that varies by tissue and condition, and it is often considered to counterbalance the effects of the AT1 receptor in cardiovascular and renal systems. Proposed roles include modulation of cell growth, inflammation, and repair, though its physiological significance can differ across contexts and remains an area of ongoing research.

In other uses, AT2 may appear as a code or acronym in technical fields, but such uses are not standardized. Context is essential to determine which meaning is intended. See also alveolar type 2 cells and angiotensin II receptors.