Aim: Protracted bacterial bronchitis (PBB) is a common cause of prolonged cough in young children, and may be a precursor of bronchiectasis. Bacteria are often present in the lower airways in both PBB and bronchiectasis and may cause persistent infections. However, there is a paucity of information available on the pathogenesis of PBB and the factors associated with persistent bacterial infection and progression to bronchiectasis. This study hypothesised that lung immune cells in recurrent PBB and bronchiectasis differentially express genes related to immune cell dysfunction compared to lung immune cells from control subjects.

Method: Cells isolated from bronchoalveolar lavage (adult‐control and PBB BAL cells) were stimulated with nontypeable Haemophilus influenzae (NTHi), and expression of genes involved in various inflammatory pathways was assessed.

Result: NTHi induced production of large amounts of IL‐1β, IL‐6, and IL‐8 in adult‐control BAL cells, however BAL cells from PBB airways appeared refractory to NTHi stimulation. BAL cells from PBB and bronchiectasis showed differential expression of several genes relative to control cells, including CCL20, MARCO, CCL24, IL‐10, PPAR‐γ, CD200R, TREM2, RelB. Expression of genes involved in resolution of inflammation and anti‐inflammation response, such as CD200R and IL‐10, was associated with the number of pathogenic bacteria found in the airways.

Conclusion: In summary, we have shown that the expression of genes related to macrophage function and resolution of inflammation are similar in PBB and bronchiectasis. Lung immune cell dysfunction in PBB and bronchiectasis may contribute to poor bacterial clearance and prolonged resolution of inflammation.