Collectins and pulmonary innate immunity

The surfactant-associated proteins SP-A and SP-D are members of a family of host defense lectins, designated collectins. There is increasing evidence that these pulmonary, epithelial-derived proteins are important components of the innate immune response to microbial challenge and participate in oth er aspects of immune and inflammatory regulation within the lung. Both prot eins bind to glycoconjugates and/or lipid moieties expressed by a wide vari ety of microorganisms, and to certain organic particles, such as pollens. S P-A and SP-D have the capacity to modulate leukocyte function and, in some circumstances; to opsonize and enhance the billing of microorganisms. The b iologic activity of cell wall components, such as Gram-negative bacterial p olysaccharides, or viral glycoproteins, such as the hemagglutinin of influe nza viruses, may be altered by interactions with collectins. In addition, c omplementary or cooperative interactions between SP-A, SP-D and other host defense lectins could contribute to the efficiency of this defense system. Collectins could play particularly important roles in settings of inadequat e or impaired specific immunity, and acquired alterations in the levels of active collectins within the airspaces and distal airways may increase susc eptibility to infection.