The human gene SFTPD produces pulmonary surfactant-associated protein D. The final processed product is a 12mer consisting of four sets of SFTPD trimer (Rust et al. 1991, Lu et al. 1992, Hakansson et al. 1999). It is secreted into the pulmonary alveoli. In addition to its surfactant-related functions, SFTPD, like SFTPA, contributes to the lung's defense against inhaled pathogens and allergens by binding and clearing these entities from the lung.