Matrix metalloproteinase-9, but not tissue inhibitor of matrix metalloproteinase-1, increases in the sputum from allergic asthmatic patients after allergen challenge

Objective: The aim of the study was to determine whether allergen inhalation modulates the levels of matrix metalloproteinase (MMP)-9 and tissue inhibitor of matrix metallloproteinase (TIMP)-1 in the induced sputum recovered from patients during a late-phase reaction. Method: Eight allergic asthma patients and five healthy control subjects inhaled a dose of Dermatophagoides pteronyssinus extract corresponding to the provocative concentration of the allergen causing a 20% fall in FEV1 and saline solution. Lung function was carefully monitored for 6 h, and an induced sputum test was performed at 6 h after sham challenge or allergen challenge. The total and differential cell counts were analyzed, and the levels of MMP-9 (by enzyme-linked immunosorbent assay [ELISA] and zymography), TIMP-1 (by ELISA), and albumin (by rocket immunoelectrophoresis) were measured. Results: The sputum eosinophil counts (p < 0.01) and MMP-9 levels (p < 0.05) increased significantly in atopic asthma patients after undergoing the allergen challenge but did not in the control subjects. By contrast, TIMP-1 and albumin levels were not significantly increased in any group. MMP-9 levels, measured after the allergen challenge in asthmatic patients, were significantly correlated with FEV1 variations after allergen inhalation (r = 0.51; p < 0.05) and with the sputum neutrophil percentage (r = 0.71; p < 0.01). Conclusion: The levels of MMP-9, but not TIMP-1, increase after inhaled allergen challenge in the sputum of allergic asthmatic patients. This protease increase may lead to a transient imbalance between MMP-9 and TIMP-1 favoring proteolytic extracellular matrix degradation.