Surfactant protein-D (SPD) is a hydrophilic protein with anti-inflammatory role and innate immune defense functions. SPD has been implicated in the development of respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD), but factors influencing its production and its normal levels in preterm infants are unknown.

We conducted a prospective, observational study, enrolling 100 extremely preterm neonates (?30 weeks? gestation), intubated for RDS and undergoing a non-bronchoscopic broncho-alveolar lavage (BAL) in the first 3h of life, before surfactant administration. SPD was assayed in BAL supernatants by ELISA. Epithelial lining fluid concentrations were obtained using serum/BAL urea ratio. Clinical data were collected in real time and were concealed to the investigators assaying SPD. Data were expressed as median [interquartile range].

SPD levels were similar in female or male, and appropriate (AGA) or small (SGA) gestational age infants, but were higher in neonates with (1138 [68-3336]) than in those without clinical chorioamnionitis (0 [0-900] ng/mL;p<0.001). SPD increased with increasing gestational age (overall p=0.03) and positively correlated with birth weight (rho=0.459; p<0.001). SPD also tended to be lower in infants who developed BPD (250 [0-1606] than in those who did not (761 [12-4400 ng/mL; p=0.05).

Overall, the levels of SPD available at the birth increase with gestational age/birth weight and in case of chorioamnionitis. The first is the consequence of the increased maturity of SPD expression and the second is likely the innate response trying to reduce the inflammatory status induced by chorioamnionitis.