CHI3L1 and bronchiolitis obliterans syndrome: Since it has been reported that MMP9 expression is closely associated with CHIT1 and YKL40 production (Malaguarnera et al., 2009; Di Rosa et al., 2014), we next investigated what component (cytoplasmic and secretory) was affected by BO treatment after 21 days from the beginning of OC differentiation.