Introduction: Eosinophilic pneumonia (EP) is characterized by a marked accumulation of eosinophils in the lungs and blood. Eosinophils and mast cells play an important role in the pathogenesis of EP via release of biomarkers such as tryptase and interleukin (IL)-33. However, the potential role of these biomarkers is not fully understood. Objectives: We aimed to evaluate the differences among the levels of tryptase and IL-33 in bronchoalveolar lavage fluid (BALF) from several types of EP. We evaluated the differences between the levels of these biomarkers in the recurrent and nonrecurrent cases. Method: We prospectively collected the clinical data of patients with EP, diagnosed between 2006 and 2015 in our institution. Bronchoscopy was performed before steroid treatment; BALF was collected. The clinical characteristics of EP patients and the levels of tryptase and IL-33 in BALF were evaluated. Results: We enrolled 15 patients with chronic EP (CEP), 5 with acute EP (AEP), 10 with drug-induced EP, and 6 with angiitis-related EP. Tryptase levels in the CEP group were significantly higher than that in the drug-induced EP group (p = 0.048), while the AEP group had the highest IL-33 levels. Recurrence of EP was noted in 67% of patients with CEP. The levels of tryptase and IL-33 were notably higher in the recurrent cases than that in the nonrecurrent CEP group (p = 0.004, p = 0.04, respectively). Furthermore, there was a positive correlation between the levels of tryptase and IL-33 in the BALF of patients with CEP (ρ = 0.69, p = 0.004). Conclusions: Tryptase and IL-33 in BALF are useful biomarkers for the assessment of EP types. These biomarkers could be used to predict disease recurrence.
