Because non-alcoholic fatty liver disease (NAFLD) is highly prevalent in obesity and T2DM, which are established risk factors for severe clinical COVID-19 disease course [13], and higher serum DPP4 enzymatic activity has been reported in patients with NAFLD [14], we hypothesized that circulating DPP4 activity might be altered in patients with acute COVID-19 disease and DPP4 might have prognostic value. Here, DPP4 is linked to type 2 diabetes mellitus.