The lung is continuously exposed to inhaled pathogens (toxic
pollutants, micro-organisms, environmental
antigens,
allergens) from the external environment. In the broncho-alveolar space, the critical balance between a measured protective response against harmful pathogens and an inappropriate inflammatory response to harmless particles is discerned by the innate pulmonary immune system. Among its many components, the
surfactant proteins and specifically the pulmonary
collectins (
surfactant proteins A [SP-A] and D [
SP-D]) appear to provide important contributions to the modulation of host defense and
inflammation in the lung. Many studies have shown that multimerization of SP-A and
SP-D are important for efficient local host defense including neutralization and opsonization of influenza A virus, binding Pneumocystis murina and inhibition of LPS-induced inflammatory cell responses. These observations strongly imply that oligomerization of
collectins is a critical feature of its function. However, during the inflammatory state, despite normal pool sizes, chemical modification of
collectins can result in alteration of their structure and function. Both pulmonary
collectins can be altered through proteolytic inactivation, nitration, S-nitrosylation, oxidation and/or crosslinking as a consequence of the inflammatory milieu facilitated by
cytokines,
nitric oxide,
proteases, and other chemical mediators released by inflammatory cells. Thus, this review will summarize recent developments in our understanding of the relationship between post-translational assembly of
collectins and their modification by
inflammation as an important molecular switch for the regulation of local innate host defense.