Innate immune collectins bind nucleic acids and enhance DNA clearance in vitro

Collectins are a class of innate immune proteins that opsonize microbes and other ligands via their carbohydrate-recognition domains and enhance their clearance by phagocytes. We hypothesized that collectins, such as pulmonary surfactant protein (SP-) A and D and mannose-binding lectin (MBL), could bind nucleic acid, which is a pentameric sugar-based anionic polymer. We have shown that SP-D and MBL bind to both DNA and RNA effectively and also that SP-D enhances the uptake of DNA by human monocytic cells. Therefore, our results suggest that nucleic acids may be a novel class of ligands for collectins. This class of innate immune proteins could enhance the clearance of DNA that is released by necrotic cells or microbial cells. Our findings may have important biological implications, such as the alleviation of DNA-mediated tissue inflammation.