Elevated lipocalin-2, matrix matalloproteinase-9 and mmp-9/lcn-2 complex serum levels in hospitalized infants with severe bronchiolitis.

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.