Pulmonary surfactant protein D (SP-D)

Pulmonary surfactant protein D (SP-D) is a hydrophilic, multimeric glycoprotein encoded by the SFTPD gene and primarily synthesized by alveolar type II cells in the lungs. It belongs to the collectin family of C-type (calcium-dependent) lectins, characterized by a collagen-like region and a C-terminal carbohydrate recognition domain. SP-D assembles as trimeric subunits into higher-order multimers and acts as a crucial component of the innate immune defense in the lung by binding a range of pathogens (bacteria, viruses, fungi) and facilitating their clearance by immune cells. Beyond pathogen clearance, SP-D regulates lung inflammation, maintains surfactant homeostasis, and dampens excessive immune activation. Variations in the SFTPD gene and alterations in SP-D levels are associated with increased risk and severity of inflammatory, infectious, metabolic, and cardiovascular diseases. Recombinant human SP-D is under investigation as a therapeutic approach for disorders such as bronchopulmonary dysplasia and other inflammatory lung diseases. Circulating SP-D is a validated biomarker for acute and chronic lung injury. Despite its therapeutic promise, challenges remain concerning the functional consequences of SP-D modification and the safety of pharmacological interventions.

Other names

Collectin-7COLEC7Lung surfactant protein DPSP-DPSPDSFTP4

Binds to carbohydrate moieties (e.g., lipopolysaccharides) on pathogens, facilitating their clearance by phagocytes; Modulates inflammatory responses by downregulating pro-inflammatory signaling (e.g., through TLR4 pathway); Dampens recruitment of inflammatory cells to lung tissue