NKX2-1 and chronic obstructive pulmonary disease: In association with decreased NKX2-1 expression in the COPD airways, reduced Clara (club) cell numbers and CC10 expression/secretion have been observed in both the peripheral and central airways of COPD patients and in cigarette smoke-exposed mouse and monkey airways (Shijubo et al., 1997; Pilette et al., 2001; Chen J. et al., 2007; Polverino et al., 2013; Barnes, 2015; Zhu et al., 2015).