Rationale: Bronchiolitis obliterans syndrome (BOS) remains the leading cause of death after lung transplantation. Treatment is difficult, although azithromycin has recently been shown to improve FEV₁. The exact mechanism of action is unclear.

Hypotheses: (1) Azithromycin reduces airway neutrophilia and interleukin (IL)-8 and (2) airway neutrophilia predicts the improvement in FEV₁.

Methods: Fourteen lung transplant patients with BOS (between BOS 0-p and BOS 3) were treated with azithromycin, in addition to their current immunosuppressive treatment. Before and 3 mo after azithromycin was introduced, bronchoscopy with bronchoalveolar lavage (BAL) was performed for cell differentiation and to measure IL-8 and IL-17 mRNA ratios.

Results: The FEV₁ increased from 2.36 (± 0.82 L) to 2.67 L (± 0.85 L; p = 0.007), whereas the percentage of BAL neutrophilia decreased from 35.1 (± 35.7%) to 5.7% (± 6.5%; p = 0.0024). There were six responders to azithromycin (with an FEV₁ increase of > 10%) and eight nonresponders. Using categorical univariate linear regression analysis, the main significant differences in characteristics between responders and nonresponders were the initial BAL neutrophilia (p < 0.0001), IL-8 mRNA ratio (p = 0.0009), and the postoperative day at which azithromycin was started (p = 0.036). There was a significant correlation between the initial percentage of BAL neutrophilia and the changes in FEV₁ after 3 mo (r = 0.79, p = 0.0019).

Conclusion: Azithromycin significantly reduces airway neutrophilia and IL-8 mRNA in patients with BOS. Responders have a significantly higher BAL neutrophilia and IL-8 compared with nonresponders and had commenced treatment earlier after transplantation. BAL neutrophilia can be used as a predictor for the FEV₁ response to azithromycin.