Surfactant protein A and Surfactant protein D (SP-A and SP-D)

Surfactant protein A (SP-A) and surfactant protein D (SP-D) are large, hydrophilic, multidomain glycoproteins of the collectin family, characterized by collagen-like regions and C-type lectin carbohydrate recognition domains. They are primarily produced by alveolar type II epithelial cells in the lung and are also found on other mucosal surfaces. Their critical function is as pattern recognition molecules in the innate immune system: they bind carbohydrates and lipids on pathogen surfaces in a calcium-dependent manner, leading to aggregation, neutralization, and enhanced clearance by phagocytes. Both SP-A and SP-D regulate inflammation—dampening excessive responses under basal conditions but supporting pro-inflammatory pathways when pathogen burden is high. They are essential for pulmonary homeostasis and protection against infection, with roles in both lung and extrapulmonary immune defense. Recombinant versions are in development as potential therapies for respiratory infections and inflammatory lung diseases[1][2][3][5][6].

Other names

Pulmonary collectinsCollectinsCollagen-containing C-type lectinsSurfactant-associated protein A (for SP-A)Surfactant-associated protein D (for SP-D)

Pathogen binding via specific recognition of carbohydrate and lipid moieties on microbial surfaces; Opsonization, facilitating clearance by phagocytes; Direct agglutination and neutralization of pathogens (reducing infectivity and enhancing clearance); Immunomodulation, including downregulation of excess inflammation and modulation of macrophage and neutrophil function[1][3][5][6].