Some examples are ABCA1 and ABCG1, downregulated in lung-resident immune cells from patients with sarcoidosis (Barna et al., 2016); compromised activity of the transcription factor liver X receptor (LXR); reduced plasma levels of alveoli-derived cholestenoic acid in patients with TB, emphysema as well as sarcoidosis (Babiker et al., 1999) and the absence of ABCG1 expression in PAP (de Aguiar Vallim et al., 2017). Here, ABCG1 is linked to pulmonary emphysema.