Time to resolution of airway inflammation caused by bronchoalveolar lavage in healthy horses

Background

Bronchoalveolar lavage (BAL) is a common procedure for evaluation of the equine lower airways. Time to resolution of post-BAL inflammation has not been clearly defined.

Hypothesis

Residual inflammation, evident by changes in immune cell populations and inflammatory cytokines, will resolve by 72 hours after BAL.

Animals

Six adult, healthy, institution-owned horses.

Methods

Randomized, complete cross-over design. Each horse underwent 3 paired BALs, including a baseline and then 48, 72, and 96 hours later, with a 7-day washout between paired BALs. Each sample underwent cytological evaluation and cytokine concentrations were determined by a commercially available multiplex bead immunoassay. Statistical analysis was performed by multilevel mixed-effects Poisson regression analysis. Data are reported as marginal means and 95% confidence interval (CI).

Results

Neutrophil, eosinophil and mast cell percentages were not significantly different at any time points. Macrophage percentages were higher at 72 hours (45.0 [95% CI, 41.6-48.4]%) and 96 hours (45.3 [95% CI, 42.9-47.7]%) vs baseline (37.4 [95% CI, 33.5-41.4]%; P < .001 and P = .01, respectively), and at 72 hours and 96 hours vs 48 hours (31.9 [95% CI, 28.1-35.6]%; P < .001). Neutrophil percentage was not significantly increased at 48 hours (P = .11). Interleukin (IL)-6 concentration was increased at 72 hours (5.22 [95% CI, 3.44-6.99] pg/mL) vs 48 hours (4.38 [95% CI, 2.99-5.78] pg/mL; P < .001).

Conclusions and Clinical Importance

Significant lung inflammation was not detected at 72 and 96 hours, suggesting that repeating BAL at 72 hours or more can be done without concern of residual inflammation.