Background: The aim of this study was to investigate the differential plasma levels of lipocalin 2 (LCN2) and its complex with MMP-9 (where MMP is matrix metalloproteinase) before and after antibiotic treatment in hospitalized adult patients with community-acquired pneumonia (CAP). Method: Plasma LCN2 and LCN2/MMP-9 complex levels were measured in 61 adult patients with CAP and 60 healthy controls using commercial enzyme-linked immunosorbent assay (ELISA). Results: A decrease in the number of white blood cells (WBCs) and neutrophils and decreases in the levels of C-reactive protein (CRP), LCN2, and LCN2/MMP-9 complex were observed after antibiotic treatment. The plasma level of LCN2, but not that of CRP, was correlated with the severity of CAP based on the Pneumonia Severity Index (PSI; r = 0.333, P = 0.009), confusion, urea, respiratory rate and blood pressure (CURB)-65 (r = 0.288, P = 0.024), and Acute Physiology And Chronic Health Evaluation II (APACHE II) scores (r = 0.328, P = 0.010). LCN2 levels were also significantly correlated with LCN2/MMP-9 levels and the numbers of WBCs or neutrophils. Conclusions: Plasma levels of LCN2 and the LCN2/MMP-9 complex can act as adjuvant diagnostic biomarkers for CAP. Plasma LCN2 might play a further role in the clinical assessment of the severity of CAP, which could potentially guide the development of future treatment strategies.
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