Increased prevalence of low oligomeric state surfactant protein D with restricted lectin activity in bronchoalveolar lavage fluid from preterm infants
- 1Department of Child Health, Institute of Molecular and Experimental Medicine, Cardiff University School of Medicine, Cardiff, UK
- 2Royal Hospital for Sick Children, Yorkhill, Glasgow, UK (current address)
- 3Department of Child Health, NIHR Respiratory Biomedical Research Unit, Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, UK
- Correspondence to Dr Eamon P McGreal, Department of Child Health, Institute of Molecular and Experimental Medicine, Cardiff University School of Medicine, Heath Park, Cardiff CF14 4XN, UK;
- Received 13 September 2012
- Revised 14 December 2012
- Accepted 11 January 2013
- Published Online First 6 February 2013
Background Surfactant protein D (SP-D) is a soluble oligomeric C-type lectin known to protect against lipopolysaccharide and ventilator-induced lung injury in preterm lambs. Here we assess the expression and functional status of SP-D in bronchoalveolar lavage fluid (BALF) from preterm infants at risk of chronic lung disease (CLD) of prematurity and term controls. This is the first systematic evaluation of SP-D function in any clinical cohort.
Methods SP-D was quantified in BALF from 28 ventilated preterm infants and five ventilated term infants. SP-D lectin activity was tested in a zymosan binding assay followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blot in BALF from the same infants. SP-D lectin activity was also tested towards maltose-agarose and mannan for selected BALF samples.
Results SP-D expression was lower on day 1 in those preterm infants who subsequently developed CLD but increased over the first 5 days of life in term and preterm neonates. The percentage of neonatal SP-D capable of binding zymosan rarely exceeded 50% in any BALF sample and was 3.5 times lower in preterm infants than term infants on day 1 of life. Similar binding defects were observed towards maltose-agarose and mannan. SDS-PAGE analysis revealed that zymosan-bound SP-D was more highly oligomerised (≥12-mers) than unbound SP-D, which was composed primarily of trimers and lower oligomeric forms.
Conclusions Substantial and functionally relevant variation in the expression and oligomeric distribution of SP-D exists between preterm and term neonatal lung secretions. This has implications for proposed SP-D replacement therapy in this population.