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. The gene discussed is CHIT1; the disease is bronchiolitis obliterans syndrome.