Decreased Neutrophil TLR4 protein expression in the airways of infants with severe RSV bronchiolitis
Session IV – Edwards, Steven – Poster Only
Title of Contribution: Decreased Neutrophil TLR4 protein expression in the airways of infants with severe RSV bronchiolitis.
Author(s): Clare P Halfhide 1 Stephen P Brearey1, Brian F Flanagan2, John A Hunt3, Deborah Howarth2, Joanne Cummerson2, Steven Edwards4, C Anthony Hart 5, Rosalind L Smyth1.
Affiliation(s): Division of Child Health1 School of Reproductive and Developmental Medicine, Divisions of Immunology2, Clinical Engineering3, Biological Sciences4 and Medical Microbiology5 University of Liverpool, Liverpool. L69 3GA, UK
Abstract:
In RSV bronchiolitis, neutrophils account for >80% of cells recovered from airways in bronchoalveolar lavage (BAL). We investigated neutrophil activation and toll-like receptor (TLR) expression in neutrophils in the blood and lungs of infants with severe RSV bronchiolitis.
Methods: BAL and blood samples were collected from 24 term and 23 preterm infants, ventilated with RSV bronchiolitis, and 12 control infants. We measured protein levels of CD11b, myeloperoxidase (MPO), and TLRs 2,4,7,8,9 and mRNA levels of TLRs 2,4,7,8,9 in neutrophils.
Results: Blood neutrophils expressed significantly higher levels of CD11b in preterm and term bronchiolitic infants, compared to controls (p < 0.025), but similar levels of MPO. BAL neutrophils from bronchiolitic infants expressed increased levels of CD11b and MPO compared to both blood neutrophils, and BAL neutrophils from controls (p < 0.01). Blood neutrophils from term RSV infants expressed lower levels of total (extracellular and intracellular) TLR4 than preterm RSV infants (p = 0.005); both expressed lower levels than controls (p < 0.04). Total TLR4 for each group was higher in BAL than blood neutrophils. Blood neutrophils from preterm RSV infants expressed higher levels of TLR4 mRNA than term RSV infants, which was similar to levels expressed in controls.
Conclusions: In infants with severe RSV bronchiolitis neutrophil activation starts in the blood and progresses as these cells are recruited into the airways. Total neutrophil TLR4 protein remains low in both compartments. This is not due to decreased expression as TLR4 mRNA expression is unimpaired. This suggests neutrophil TLR4 protein expression is deficient in these infants, which could help explain why they develop severe RSV bronchiolitis.
