THY1 and hypersensitivity pneumonitis: Consistently, increased fibroblast proliferation in the absence of Thy-1 expression has also been described in fibrotic foci in lungs of patients with pulmonary fibrosis and fibroblasts derived from patients with hypersensitivity pneumonitis, supporting the idea that Thy-1 expression is necessary to avoid fibrosis (Ramirez et al., 2011).