MUC1 and COVID-19: Similarly, although serum KL-6 levels were increased in hospitalized COVID-19 patients with SARS-CoV-2-mediated pulmonary fibrosis (n = 12) compared to hospitalized COVID-19 patients without pulmonary fibrosis (n = 10), serum KL-6 levels tended to decrease after hospital discharge in a time-dependent manner correlating with the resolution of pulmonary fibrosis [131].