MUC1 and hypersensitivity pneumonitis: Quite notably, one article (9) reported that KL-6 concentrations were significantly higher in the serum of HP patients exposed to birds with fibrotic patterns than in healthy controls (2805.6 ± 5346.9 vs. 283.7 ± 282.6 U/ml, P<0.0001), and serum KL-6 concentrations were also significantly higher in fibrotic HP patients exposed to fungi compared with the healthy controls (1590.3 ± 2604.1 vs. 283.7 ± 282.6 U/ml, P<0.0001).