Structure, genetics and function of the pulmonary associated surfactant proteins A and D: The extra-pulmonary role of these C type lectins

The collectins family encompasses several collagenous Ca2+-dependent defense lectins that are described as pathogen recognition molecules. They play an important role in both adaptive and innate immunity. Surfactant proteins A and D are two of these proteins which were initially discovered in association with surfactant in the pulmonary system. The structure, immune and inflammatory functions, and genetic variations have been well described in relation to their roles, function and pathophysiology in the pulmonary system. Subsequently, these proteins have been discovered in a wide range of other organs and organ systems. The role of these proteins outside the pulmonary system is currently an active area of research. This review intends to provide a current overview of the genetics, structure and extra-pulmonary functions of the surfactant collectin proteins.