Langerin (CD207) is a type II transmembrane glycoprotein which is member K of the C-type lectin domain family 4. Langerin is used as a marker for Langerhans cells (LCs) which represent the immature dendritic cells in the epidermis. LCs uniquely contain tennis racket-shaped endosomal recycling compartment subdomains with pentalamellar membranes termed Birbeck granules. Langerin is necessary and sufficient for Birbeck granule formation.
Langerin also mediates endocytosis of non-peptide antigens containing mannose, N-acetyl glucosamine and fucose that are expressed by mycobacteria and fungae. Some antigens, such as the M. leprae glycolipid arabinomycolate, are ultimately presented by human LC CD1a in cutaneous-draining lymph nodes. Langerin performs a barrier-like function to HIV-1 transmission due to its internalization of virus particles for destruction. A rare human polymorphism within the lectin domain, W264R, abolishes both carbohydrate recognition and Birbeck granule formation. Genetic deletion of mouse langerin was not shown to have functional consequence other than abolishing Birbeck granule formation. Human langerin shares 68%, 62%, 71% aa identity with mouse, rat and bovine langerin ECD, respectively.