SP-A and SP-D are members of the collectin family of oligomeric proteins, which have collagen-like N-terminal regions and C-type carbohydrate recognition domains (CRDs). The CRDs bind carbohydrates such as those found on pathogen surfaces. SP-A consists of 6 structural units, which are assembled into a “flower bouquet” formation. SP-D consists of the tetrameric structural units assembled into an X-like structure. Figure adapted from an online article by N. Kawasaki that appears on Glycoforum(http://www.glycoforum.gr.jp/science/word/lectin/LEA06E.html).