Serum legumain is a potential biomarker for community-acquired pneumonia: a prospective cohort study

<b>Background:</b> Legumain is a cysteine endopeptidase that belongs to the C13 family. Many studies have revealed that legumain plays a vital pathogenic role in various respiratory diseases. The aim of this study was to explore the role of legumain in community-acquired pneumonia (CAP). <b>Methods</b>: Serum samples were collected from 293 CAP patients on admission. The concentration of serum legumain was detected via an enzyme-linked immunosorbent assay. The relationship between serum legumain and CAP was assessed. <b>Results</b>: Serum legumain concentrations were increased in severe CAP patients compared to the concentrations of mild CAP patients. The Spearman rank correlation coefficient suggested that the serum legumain concentration was strongly associated with many clinical indicators. Additionally, linear regression analysis revealed that the serum legumain concentration was positively correlated with the CURB-65, PSI, SMART-COP, and APACHE II scores. Moreover, the serum legumain concentration on admission was elevated in CAP patients who underwent mechanical ventilation, vasoactive agent therapy, ICU admission, and who died during hospitalization. CAP patients with higher serum legumain expression had poor prognostic outcomes. The predictive value of the serum legumain concentration for prognosis was similar to that of the severity score. <b>Conclusions</b>: Serum legumain concentration is positively related to disease severity and a poor prognosis, indicating that serum legumain can be used as an indicator of disease severity and a prognostic indicator for CAP patients.