Matrix Metalloproteinase-9 in Peripheral Blood Eosinophils

BACKGROUND: Matrix metalloproteinases (MMPs) are major contributors to tumor invasion, remodeling of connective tissue and infiltration of inflammatory cells and may be important mediators in developing allergic inflammation. Overexpression of MMP-9 mRNA by eosinophils in the asthmatic airways has been reported. To clarify the relative significance of MMP as an inflammatory mediator from eosinophils, we determined the content of MMP-9 in the peripheral blood eosinophils and compared it with the other leukocyte fractions. METHODS: Peripheral blood eosinophils, neutrophils, and mononuclear cells were purified from normal and allergic donors with Percoll gradient centrifugation and CD16 negative selection. Cell lysate and culture supernatants stimulated with IL-5, PAF, and PMA were tested for MMP-9 with gelatin zymography and ELISA. RESULTS: The amount of MMP-9 in highly purified eosinophils, neutrophils, and mononuclear cells was 2.5 +/- 0.9, 4,073 +/- 581, and 7.6 +/- 1.4 ng/5 x 10(6) cells, respectively. There was no difference in MMP-9 content of eosinophils between normal donors and patients with asthma. Culture of peripheral blood eosinophils with IL-5 for 4 days did not induce MMP-9 production. The stimulation of eosinophils with PMA and other secretogogues caused only small amounts of MMP-9 secretion as compared with neutrophils. CONCLUSIONS: These findings suggest that circulating eosinophils normally have only small amounts of MMP-9 and that eosinophils may need complex activation signals to produce significant amounts of MMP as seen in tissues of allergic inflammation.