To clarify whether the distribution and differentiation of Th9 cells are altered in the lungs of patients with IPF, we examined PU.1 (the specific transcription factor of Th9 cells) in the lung tissues of patients with IPF (n = 14) and controls (n = 4) by immunohistochemistry (Table 2). The gene discussed is SPI1; the disease is idiopathic pulmonary fibrosis.