Nontypeable Haemophilus influenzae supresses SP-B and SP-C expression in alveolar epithelial type II cells

Background: Chronic obstructive pulmonary disease (COPD) is characterized by progressive loss of lung tissue and lung function. Nontypeable Haemophilus influenzae (NTHi) frequently colonizes the lungs of stable COPD patients and is associated with acute exacerbations. Alveolar type II cells secrete surfactant and give rise to type I cells. Aim: To investigate the effect of NTHi on the differentiation of murine pneumocytes. Methods: Primary murine alveolar epithelial cells were isolated from wildtype and mice double deficient for Toll-like receptor 2 and 4 and cultured directly on transwells. To generate air-liquid interface (ALI) cultures the apical medium was removed 48 hours after isolation. ALIs were inoculated with inactivate NTHi at the day of airlift or 24 hours post airlift. The transepithelial electrical resistance (TEER), the expression of differentiation markers, and the release of cytokines were determined. Results: Exposure to NTHi at day of the airlift resulted in an increased TEER and a decreased expression of the surfactant proteins SP-B and SP-C independent of TLR-2/4. Deficiency for TLR-2/4 resulted in a decreased release of the inflammatory cytokine keratinocyte-derived chemokine (KC). Exposure to NTHi 24 hours post airlift resulted in a decreased expression of SP-B and SP-C, but did not significantly affect the TEER. Tight junction gene expression (e.g. Occludin, Zo-1) was not significantly affected by exposure to NTHi. Conclusion: Our data indicate that exposure to NTHi suppresses the expression of surfactant protein B and C in alveolar type II cells independent of TLR-2/4.