Surfactant proteins SP-A and SP-D as modulators of the allergic inflammation in asthma

Surfactant proteins A and D (SP-A and SP-D) are members of the collectin family and bind to various motifs of microorganisms, particles and allergens. They play an important role in the first-line defense within the lung. Recent research has highlighted that these proteins not only augment innate immune responses to invading microorganisms but also act on adaptive immune functions like dendritic cell maturation and T cell proliferation. Both SP-A and SP-D downregulate the eosinophilic inflammation in murine asthma models and shift the cytokine profile towards a T helper cell type 1 response. In addition, they are effective at alleviating bronchial hyperresponsiveness. Although our knowledge about surfactant proteins as modulators of the allergic inflammatory reaction in asthma is still limited, the idea that surfactant proteins play a role in asthma has attracted increasing attention. In this review, the impact of the lung collectins SP-A and SP-D on asthmatic allergic inflammation and vice versa will be discussed.