Porcine Lung Surfactant Protein D: Complementary DNA Cloning, Chromosomal Localization, and Tissue Distribution

Abstract

Porcine organs and lung surfactant have medically important applications in both xenotransplantation and therapy. We have started to characterize porcine lung surfactant by cloning the cDNA of porcine surfactant protein D (SP-D). SP-D and SP-A are important mediators in innate immune defense for the lung and possibly other mucosal surfaces. Porcine SP-D will also be an important reagent for use in existing porcine animal models for human lung infections. The complete cDNA sequence of porcine SP-D, including the 5′ and 3′ untranslated regions, was determined from two overlapping bacteriophage clones and by PCR cloning. Three unique features were revealed from the porcine sequence in comparison to SP-D from other previously characterized species, making porcine SP-D an intriguing species addition to the SP-D/collectin family. The collagen region contains an extra cysteine residue, which may have important structural consequences. The other two differences, a potential glycosylation site and an insertion of three amino acids, lie in the loop regions of the carbohydrate recognition domain, close to the carbohydrate binding region and thus may have functional implications. These variations were ruled out as polymorphisms or mutations by confirming the sequence at the genomic level in four different pig breeds. Porcine SP-D was shown to localize primarily to the lung and with less abundance to the duodenum, jejunum, and ileum. The genes for SP-D and SP-A were also shown to colocalize to a region of porcine chromosome 14 that is syntenic with the human and murine collectin loci.

Porcine Pulmonary Collectins Show Distinct Interactions with Influenza A Viruses: Role of theN-Linked Oligosaccharides in the Carbohydrate Recognition Domain

“…Characterization of porcine SP-D (pSP-D) by cDNA cloning revealed that pSP-D has structurally unique features that have not been found in SP-D from other species examined to date (26). These include a cysteine within the collagen domain, an insertion of 3 aa in the CRD and the presence of a terminally sialylated N-linked sugar within the CRD (27).…”

A Unique Sugar-binding Site Mediates the Distinct Anti-influenza Activity of Pig Surfactant Protein D

“…Our investigations into the primary structure and biochemical properties of porcine SP-D (pSP-D) have revealed that pSP-D is unique in that it is the only SP-D species known to be equipped with an N-linked complex sialic acid-rich glycan in its CRD (10,20). These sialic acids are likely to interact with the conserved sialic acid receptor, located on the HA of all IAVs, that mediates binding of the virus to sialoglycans expressed on the respiratory epithelium, initiating IAV infection of the lung.…”

Pulmonary infections in swine induce altered porcine surfactant protein D expression and localization to dendritic cells in bronchial‐associated lymphoid tissue

“…The pSP-D cDNA sequence has been determined, 14 the pSP-D protein has been purified and characterized, 15,16 and the interaction between pSP-D and influenza A virus described. 17,18 Furthermore, pSP-D was found to be immunolocalized in normal tissues (predominantly in Clara cells and in serous cells of the bronchial submucosal glands) and, to a lesser extent, in alveolar type II cells, in epithelial cells of the intestinal glands (crypts of Lieberkühn) in the duodenum, jejunum and ileum, and in serous cells of the dorsolateral lacrimal gland.…”