Background Patients with COPD have a susceptibility to respiratory tract infections associated with increased pulmonary inflammation. Bacteria can reside within the host as cell-associated (attached to host cells via adhesins, pili or biofilm formation) or cell-dissociated bacteria. It is unclear how bacteria-to-cell interactions affect pulmonary inflammation and whether these levels differ over an exacerbation time course. We sought to investigate the effects of Haemophilius influenzae cell-interaction upon airway inflammation and whether the levels of H. influenzae bacteria and cell-dissociated bacteria differ over an exacerbation time course.

Methods Cell differential counts were carried out on sputum samples as per standard protocol. Bacterial DNA was extracted and H.influenzae was quantified using qPCR from the sputum plug (contains cell-associated and dissociated bacteria) and the sputum cell-free supernatant (cell-dissociated bacteria only). Inflammatory mediators (IL-1α, TNF-α, IL-8 and neutrophil elastase (NE)) were measured in the sputum supernatant using commercial assays.

Results 63 patients (77% male; average age of 69 (45–88); FEV₁ percentage predicted of 53%; mean percentage neutrophil count in sputum of 65%) at stable state were analysed. Levels of H. influenzae in the supernatant only correlated with the sputum total cell count (r=0.38; p=0.03). Levels of H. influenzae in the plug correlated with inflammatory mediators (sputum neutrophil percentage r=0.42, p=0.01; sputum macrophage percentage r=−0.35, p=0.04; IL-1α r=0.36, p=0.03; IL-8 r=0.49, p<0.01; NE r=0.40, p=0.02). The exacerbation time course in 10 paired COPD subjects was examined. There was no significant difference in H. influenzae levels in the plug (p=0.89) (figure 1A). However, there was a significant increase in levels in the supernatant over the exacerbation time course (p=0.05) (figure 1B).

Conclusion H. influenzae levels in the sputum plug appear to have much more of an effect on airway inflammation than levels of cell-dissociated H. influenzae suggesting that cell-associated bacteria may be a driver of airway inflammation in COPD. Further investigation into this highly complicated relationship needs to be conducted.

• Download figure
• Open in new tab
• Download powerpoint

Abstract S116 Figure 1

Levels of H. influenzae in the sputum plug (A) and in the sputum supernatant (B) during an exacerbation time course in 10 paired subjects with COPD.