Upregulation of Alveolar Levels of Activin B, but not Activin A, in Lungs of West Highland White Terriers with Idiopathic Pulmonary Fibrosis and Diffuse Alveolar Damage

Summary Activins, cytokines belonging to the transforming growth factor-β superfamily, have an important role in inflammation and fibrosis. Activin A has been suggested to participate in the pathophysiology of human idiopathic pulmonary fibrosis (IPF), but studies on the role of activin B are sparse. Canine IPF (CIPF) is an incurable interstitial lung disease occurring particularly in West Highland white terriers (WHWTs). During the disease course there are acute exacerbations (AEs) and the condition has a poor prognosis. Microscopically, AEs of CIPF are characterized by diffuse alveolar damage, which is also a key feature of acute respiratory distress syndrome (ARDS). The aim of this study was to study expression of activin A and B in lung tissue of WHWTs with CIPF and WHWTs with CIPF and concurrent AE, and dogs of various breeds with ARDS and to compare these findings with those of healthy WHWTs. In addition, western blot analysis of activin B from bronchoalveolar lavage fluid (BALF) from WHWTs with CIPF and healthy WHWTs was conducted. Activin B, but not activin A, was strongly expressed in the altered alveolar epithelium in the lungs of WHWTs with CIPF as well as in the lungs of dogs with ARDS. Activin B was detected in the BALF of WHWTs with CIPF, most notably in samples from dogs with AE, but activin B was not detected in BALF from healthy WHWTs. These findings suggest that activin B may be part of the pathophysiology of CIPF and might act as a marker of alveolar epithelial damage.