In order to evaluate the aberrant behavior of club cells in a semi-quantitative manner, two sets of samples (lung sections from IPF and COPD patients; n=6 each) immunohistochemically labeled for Cldn10 were microscopically analyzed using three independent histopathological parameters as follows: (i) hype-rcellularity of Cldn10-positive cells in bronchiolar epithelium, (ii) cellular mass in the airspace containing Cldn10-positive cells, and (iii) infiltration of Cldn10-positive cells into thickened interstitium (Table 1). The gene discussed is CLDN10; the disease is idiopathic pulmonary fibrosis.