Abstract
Bronchiolitis is the leading cause of hospitalization for lower respiratory tract infections in infants under one year, often triggered by respiratory syncytial virus. Neutrophil-driven inflammation plays a key role in disease severity. Lipocalin-2 (LCN-2), matrix metalloproteinase-9 (MMP-9), and their complex (MMP-9/LCN-2) are involved in neutrophil activity and tissue remodeling, but their role in infant bronchiolitis remains unexplored. In the present study serum levels of LCN-2, MMP-9, and MMP-9/LCN-2 complex in infants hospitalized with bronchiolitis have been measured and correlated with clinical and hematological parameters to assess their potential as biomarkers of disease severity. A prospective cohort study enrolled fifty-six infants under 1 year of age admitted with diagnosis of bronchiolitis at the Policlinico Umberto I hospital of Rome. The score of clinical severity was assessed at admission and during hospitalization. The most severe score and oxygen supplementation requirement were recorded. Serum levels of LCN-2, MMP-9, and MMP-9/LCN-2 complex were measured via ELISA. Infants requiring oxygen supplementation had significantly elevated serum levels of LCN-2, MMP-9, and the MMP-9/LCN-2 complex. These markers positively correlated with neutrophil and total white blood cell counts. Gender-specific analysis showed higher LCN-2 and MMP-9/LCN-2 levels in males. LCN-2 and MMP-9, particularly in complexed form, are upregulated in more severe bronchiolitis cases and may reflect neutrophil-driven inflammation. These findings suggest a potential role for these biomarkers in stratifying disease severity and possibly predicting long-term respiratory outcomes. Further studies are needed to validate their clinical utility in larger pediatric populations. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-025-21976-6.