ABSTRACT
Surfactant proteins A (SP-A) and D (SP-D) are soluble host defense pattern recognition collectins that recognize carbohydrate arrays present on broad spectrum of microbes [1-3]. These proteins and serum collectin mannan-binding lectins (MBL) preferentially bind carbohydrate and lipid moieties
via their globular domains to facilitate immune functions such as agglutination of bacteria, neutralization of viruses, and clearance of bacteria and fungi. SP-A and SP-D also interact with immunoglobulins, complement component C1q, and receptors present on adaptive and innate immune cells that results in enhanced microbial clearance and reduced lung in ammation [4,5]. Both of these collectins also recognize apoptotic immune cells and their components to mediate their clearance. These proteins, particularly SP-D, regulate lipid homeostasis in the lung [6-8]. Although SP-A is primarily con ned to the respiratory system, SP-D is present in several extrapulmonary tissues and at mucosal surfaces. Notably, concentrations of SP-A and SP-D are signi cantly altered in lung washing as well as in serum during several disease conditions. Furthermore, certain genetic polymorphisms of SP-D (Met11Thr) are known to alter the oligomeric assembly of the protein. Therefore, these collectins may be used as valuable disease markers.
