Pulmonary surfactant-associated protein D (SP-D) (SP-D)

Pulmonary surfactant-associated protein D (SP-D) is a large multimeric glycoprotein belonging to the collectin family of the innate immune system [1]. It is primarily secreted by alveolar type II cells and Clara cells in the lungs, where it plays a critical role in maintaining pulmonary homeostasis and defending against inhaled pathogens [4]. SP-D functions as a pattern recognition receptor (PRR), utilizing its C-terminal carbohydrate recognition domain (CRD) to bind specifically to pathogen-associated molecular patterns (PAMPs), such as the β-glucans found in the cell walls of Saccharomyces cerevisiae and other fungi [2, 3]. This binding leads to the aggregation and opsonization of the microorganisms, significantly enhancing their clearance by alveolar macrophages through phagocytosis [2]. Beyond its role in infection, SP-D modulates inflammatory responses by interacting with various immune cell receptors to regulate cytokine production [1]. Clinically, SP-D is utilized as a serum biomarker for lung injury and interstitial lung diseases, as its levels reflect the state of the alveolar-capillary barrier [5]. Therapeutic development focuses on recombinant human SP-D (rhSP-D) to treat neonatal respiratory distress syndrome and prevent secondary infections in chronic lung diseases [5].

Other names

SFTPDSurfactant protein DCollectin-7COLEC7PSP-D

SP-D acts as an opsonin by binding to carbohydrate structures on pathogens via its C-type lectin domain, facilitating their recognition and ingestion by phagocytes.