Neutrophil TLR4 expression is reduced in the airways of infants with severe bronchiolitis

Abstract

Background:In respiratory syncytial virus (RSV) bronchiolitis, neutrophils account for >80% of cells recovered from the airways in bronchoalveolar lavage (BAL) fluid. This study investigated neutrophil activation and Toll-like receptor (TLR) expression in the blood and lungs of infants with severe RSV bronchiolitis.Methods:BAL fluid and (blood) samples were collected from 24 (16) preterm and 23 (15) term infants ventilated with RSV bronchiolitis, and 12 (8) control infants. Protein levels and mRNA expression of CD11b, myeloperoxidase (MPO) and TLRs 2, 4, 7, 8 and 9 were measured in neutrophils.Results:Blood neutrophils had more CD11b in preterm and term infants with RSV bronchiolitis than control infants (p<0.025) but similar amounts of MPO. BAL fluid neutrophils from infants with RSV bronchiolitis had greater amounts of CD11b and MPO than blood neutrophils and BAL fluid neutrophils from controls (p<0.01). Blood neutrophils from term infants with RSV bronchiolitis had less total TLR4 protein than preterm infants with RSV bronchiolitis (p = 0.005), and both had less than controls (p<0.04). Total TLR4 for each group was greater in BAL fluid neutrophils than in blood neutrophils. Blood neutrophils from preterm infants with RSV bronchiolitis had greater TLR4 mRNA expression than term infants with RSV bronchiolitis (p = 0.005) who had similar expression to controls (p = 0.625).Conclusions:In infants with severe RSV bronchiolitis, neutrophil activation starts in the blood and progresses as they are recruited into the airways. Total neutrophil TLR4 remains low in both compartments. TLR4 mRNA expression is unimpaired. This suggests that neutrophil TLR4 expression is deficient in these infants, which may explain why they develop severe RSV bronchiolitis.

Attenuated Bordetella pertussis Vaccine Protects against Respiratory Syncytial Virus Disease via an IL-17–Dependent Mechanism

“…Human studies also indicate an important role for neutrophils, linking neutrophils with impaired TLR4 signaling to severe RSV bronchiolitis (31). In the present studies we found that BPZE1 inoculation resulted in a very moderate neutrophil recruitment (,12% of BAL cells), and BPZE1 colonization caused no lung inflammation or neutrophil excess by Day 7 after infection, suggesting that BPZE1-mediated recruitment of neutrophils does not contribute to airway inflammation.…”

Local cytokine response upon respiratory syncytial virus infection

“…For instance, it has been described that expression of TLR4 is significantly increased in epithelial cells after RSV challenge and during the inflammatory response induced by the virus [30]. Consistent with this observation, neutrophils recovered from bronchoalveolar lavages of RSV-infected preterm infants expressed significantly higher levels of TLR4 than did healthy infants, suggesting an increased inflammatory potential in those patients [31]. Furthermore, a recent study has also shown that RSVinfected human bronchial epithelial cells secrete the heat shock protein HSP72, which binds to TLR4 on neutrophils and leads to an increase on IL-8 and TNF-␣ production [32].…”

Reduced Nasal Viral Load and IFN Responses in Infants with Respiratory Syncytial Virus Bronchiolitis and Respiratory Failure

“…In severe RSV bronchiolitis it has been shown that the virus undergoes transcription in blood neutrophils (41), and that neutrophil TLR4 expression and function is reduced in the blood and airways (42), with distinct blood neutrophil subsets in severe viral infection (43). Interestingly, in our study gene expression of several granzymes and antimicrobial peptides (CAMP and DEFA1) associated with neutrophils were clustered with type-I IFNs, but were not significantly differentially expressed between severity groups.…”