Anti-Surfactant Protein D antibodies are used in the immunodetection of the protein encoded by the SFTPD gene. In humans, the canonical protein has a reported length of 375 amino acid residues and a mass of 37.7 kDa. Its subcellular localization is in the extracellular matrix and is also secreted. It is reported to be expressed in the lung, brain, pancreas and adipose tissue (mainly mature adipocytes). A member of the SFTPD protein family, it is said to contribute to the lung's defense against inhaled microorganisms, organic antigens and toxins. Post-translational modifications have been described, including glycosylation. Other names for this target antigen include PSP-D, SFTP4, SP-D, pulmonary surfactant-associated protein D, collectin-7, and COLEC7.