Bronchoalveolar lavage and serum KL-6 concentrations in chronic hypersensitivity pneumonitis: correlations with radiological and immunological features

Chronic hypersensitivity pneumonitis (cHP) is a fibrotic interstitial lung disease (ILD) resulting from inhalation of different organic substances and chemical compounds determining an inflammatory and immunological response in sensitized individuals. KL-6, a human mucin protein expressed by type 2 pneumocytes, has been proposed as a prognostic biomarker of cHP. Assessment of usefulness KL-6 in ILD has been investigated primarily in Asiatic population. The aim of this study was to evaluate clinical utility of KL-6 in serum and bronchoalveolar lavage (BAL). In this study, we retrospectively analysed clinical, radiological and immunological data of a cohort of 42 patients affected by cHP: KL-6 concentrations were collected from serum and BAL. KL-6 clinical value was assessed through the analysis of association between KL-6 concentrations and clinical, functional, immunological and radiological features. KL-6 serum concentration results increased in 28/34 patients (82%). A positive direct correlation was observed between KL-6 concentrations in BAL and serum (r = 0.62, p < 0.05). In our study population we found that patients with extensive presence of ground glass opacities and centrilobular nodules at high-resolution computed tomography (HRCT) showed the highest concentrations of KL-6 in BAL and a predominantly CD3+ CD8+ BAL lymphocytosis. BAL lymphocytosis and KL-6 concentrations showed a direct correlation. BAL KL-6, a result of alveolar damage, caused in cHP by CD3+ CD8+ mediated flogosis and suggested by radiological evidence of ground-glass opacities and centrilobular nodules, can be considered a useful biomarker to assess, along with BAL cellular analysis and HRCT findings, disease activity.