One function of the pulmonary collectins, surfactant proteins A1, A2, A3 and D (SFTPAs, D), is that they influence surfactant homeostasis, contributing to the physical structures of lipids in the alveoli and to the regulation of surfactant function and metabolism. They are directly secreted from alveolar type II cells into the airway to function as part of the surfactant. The mechanism of secretion is unknown. Mutations in SFTPA2 disrupt protein structure and the defective protein is retained in the ER membrane causing idiopathic pulmonary fibrosis (IPF; MIM:178500). Mutations that cause IPF are G231V and F198S (Wang et al. 2009).
Loss of function of SFTPA2 mutants [endoplasmic reticulum membrane]