IDO1 and atherosclerosis: Mechanically, accumulating studies have implicated IDO1 expression on pDCs was necessary to confer suppressive function to Tregs in many diseases such as melanoma, experimental autoimmune encephalomyelitis (EAE), rheumatoid arthritis and atherosclerosis (Kavousanaki et al., 2010; Chevolet et al., 2015; Lippens et al., 2016; Yun et al., 2016).