Aquaporin 5 (AQP5) is a water channel protein that plays a significant role in the generation of saliva, tears, and pulmonary secretions. It is a member of the major intrinsic protein family, characterized by its ability to selectively transport water across cell membranes. AQP5 is predominantly expressed in the salivary and lacrimal glands, as well as in the respiratory tract, and is crucial for maintaining water homeostasis within these secretions. The protein is also implicated in the pathogenesis of certain diseases, such as Sjögren's syndrome, where its abnormal subcellular distribution in salivary gland cells may contribute to the disease's development.