The lectin and surfactant SP-D is a secreted component of the innate immune system known mainly for its presence and function in the lungs. In the Proceedings of the National Academy of Sciences USA, Taniguchi and colleagues find that SP-D is also generated by epithelial cells in the gallbladder, but nowhere else within the digestive system or in the liver. SP-D is secreted into the intestine as a component of bile; once there, it binds particular commensals such as Lactobacillus species. Deficiency in SP-D results in dysbiosis, including a reduction in the abundance of Clostridia species, which have been linked to the homeostasis of regulatory T cells. SP-D-deficient mice also exhibit worse experimentally induced colitis. The apparently unique production of SP-D within the digestive system has potentially important implications for otherwise routine gallbladder removal (cholecystectomy).

Proc. Natl. Acad. Sci. USA (19 Sep 2017) doi:10.1073/pnas.1712837114