Surfactant protein D contributes to the lung's defense against inhaled microorganisms. It's a calcium ion dependent carbohydrate binding protein and is structurally similar to other C type mammalian lectins, such as conglutinin and SPA. It has a molecular size of approximately 37-43kDa in its reduced state, 620kDa in non dissociating conditions. Surfactant protein D enhances the production of oxygen radicals by rat alveolar macrophages and regulates some actions of SPA, which is the most abundant surfactant protein. Surfactant protein D is synthesized and secreted by alveolar epithelial type II cells. Also known as:pulmonary surfactant-associated glycoprotein D; COLEC 7; COLEC7; Collectin7; PSP D; PSPD; Pulmonary surfactant apoprotein; Pulmonary surfactant associated protein D; SFTP 4; SFTP4; SFTPD; SP D; Surfactant associated protein pulmonary 4; Surfactant pulmonary associated protein D