Surfactant Protein D / SP-D (BSB-162), MMab

Surfactant protein D, also known as SFTPD or SP-D, is a protein encoded by the SFTPD gene. Pulmonary surfactants are essential to proper respiratory structure and function, consisting of ~90% lipids (mostly phospholipids) and 8–10% surfactant-associated proteins. SP-D is a pattern-recognition molecule in the collectin (collagen-containing C-type lectin) family. In the lungs, it is an opsonin that can agglutinate a range of microbes and enhance their clearance via phagocytosis and super-oxidative burst. It can interfere with allergen–IgE interaction and suppress basophil and mast cell activation.

Other surfactant proteins like SP-B and SP-C showed strong immunohistochemical expression in Lung Hyperplasias and Adenomas, suggesting that SP-B and SP-C are related to lung tumorigenesis. SP-D is likely an innate immune surveillance molecule against tumor development. SP-D suppresses Lung Cancer progression via interference with epidermal growth factor signaling, and a truncated recombinant human SP-D may induce apoptosis in Pancreatic Adenocarcinoma via Fas-mediated pathway in a p53-independent manner. Studies Have found low expression of Surfactant protein D antibody expression in Lung, Gastric, and Breast cancers and high expression in different stages and grades of Ovarian cancer. Surfactant protein D antibody expression could be associated with a favorable prognosis in Lung Cancer but unfavorable in non-pulmonary sites such as Gastric, Breast, and Ovarian cancers. SP-D detected in circulating tumor cells of Ovarian Cancer patients suggests SP-D can also be used as a potential biomarker.

The purified Spike protein of SARS-CoV-2 bound to Vero but not 293T cells and was itself recognized by SP-D, in the lung alveoli. It suggests that SARS-CoV interacts with innate immune mechanisms in the lung through its S-protein and regulates pulmonary inflammation.