Background: The purpose here was to detect the association among plasma matrix metalloproteinase-9 (MMP-9) concentration, single nucleotide polymorphisms (SNPs) of MMP-9 gene and community-acquired pneumonia (CAP). Methods: The enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) were, respectively used to measure the plasma MMP-9 level and its gene polymorphisms. Results: The level of plasma of MMP-9 was elevated in patients with CAP as compared to that of normal controls and decreased significantly after treatment. Plasma MMP-9 concentration was significantly correlated with white blood cell (WBC) and neutrophil counts in patients with CAP. No significant difference was found in the genotypes distribution of MMP-9 SNPs, rs3918242, rs17576 or rs2274756, between patients with CAP and normal controls. Plasma MMP-9 concentration was not associated with MMP-9 polymorphism. When the cut-off level of the plasma MMP-9 concentration was set to be 105.02 ng/mL, the odds ratio of plasma MMP-9 for CAP risk was 9.86 (95 confident interval: 4.2722.75). Plasma MMP-9 level may act as a prediction marker for CAP. Conclusions: Elevated plasma MMP-9 could be a biological marker for the diagnosis and be a new strategy for target therapy of community-acquired pneumonia.
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