Matrix metalloproteinase-9 in myeloid cells: implications for allergic inflammation

Matrix metalloproteinase-9 (MMP-9; 92 kDa gelatinase) is utilized by myeloid and lymphoid cells for migration across basement membranes. Although eosinophils are commonly seen infiltrating asthmatic airways, the role of basophils in allergic inflammation is debated. This study was undertaken to evaluate the content of MMP-9 in purified basophils compared with eosinophils and neutrophils. Peripheral blood basophils were isolated to greater than 95% purity using negative selection with antibody-coated magnetic beads using a 12-antibody cocktail. Eosinophils of greater than 98% purity were obtained by negative selection and neutrophils by positive selection using anti-CD16 magnetic beads. MMP-9 activity was assessed by gelatin zymography of cell lysates. Under parallel conditions, neutrophils contained 1,000-fold more MMP-9 than eosinophils. No activity was detected from 2x10(5) basophils. Immunocytochemistry with an anti-MMP-9 antibody showed bright staining of all neutrophils, lesser staining of eosinophils and no detectable staining of basophils. The failure to find MMP-9 in basophils may explain their paucity in asthmatic airway inflammation or suggest they secrete other enzymes capable of degrading type IV collagen.