SFTPD, as known as Surfactant pulmonary-associated protein D, is a member of the collectin family of C-type lectins that is synthesized in many tissues including respiratory epithelial cells in the lung, and contains one C-type lectin domain and one collagen-like domain. It is humoral molecules of the innate immune system, and is considered a functional candidate in chronic periodontitis. Besides it is involved in the development of acute and chronic inflammation of the lung. Several human lung diseases are characterized by decreased levels of bronchoalveolar SFTPD. Recombinant human SFTPD protein, fused to His-tag at N-terminus, was expressed in E.coli