DPP4 and immune system disorder: High levels of IL-5 have been documented in the BAL of CEP patients, consistent with this being a Th2 type inflammatory disease.15 CD26 and T cells have an important role in the pathogenesis of asthma.6,7 In contrast to our data, increased levels of sCD26 have been reported in patients with presumed Th2-like immune disease, such as atopic dermatitis.8 Recently Eltzching et al. also reported that hypoxemia induced endothelial CD26 at both the mRNA and protein.16 In the present study, serum levels of sCD26 were, however, inversely correlated with the disease activity of CEP patients.