C5a mediates secretion and activation of matrix metalloproteinase 9 from human eosinophils and neutrophils

Matrix metalloproteinase 9 (MMP-9) is a crucial proteinase, utilized by both eosinophils and neutrophils, that mediates transmigration through extracellular basement membranes. We have found that neutralization of MMP-9 by a monoclonal antibody or a chemical inhibitor blocked C5a dependent chemotaxis of these granulocytes in vitro. The levels of MMP-9 secreted by the action of C5a from eosinophils were about 50-fold lower than those from neutrophils, consistent with results from confocal microscopy, where the density of MMP-9 containing granules was fewer within eosinophils than in neutrophils. Zymography indicated gelatin degrading activity of the molecular size of proMMP-9 in supernatants from eosinophils and neutrophils stimulated by C5a, with no evidence of proteolytic activation. Instead MMP-9 activation appeared oxidative, since inhibition of NADPH oxidase and nitric oxide synthase by DPI or L-NIL abrogated C5a-mediated chemotaxis through basement membranes. In keeping with this mode of activation, C5a, known as an agent of superoxide generation, was also found to induce secretion of nitric oxide from human eosinophils and rat granulocytes and monocytes. In conclusion C5a is an important mediator that brings about secretion and oxidative activation of MMP-9, a requisite protease for transmigration, from both eosinophils and neutrophils.