FIG. 5.

Proteolytic effector function: chemokine gradient formation. The schematic diagrams depict the migration (extravasation, intraparenchymal homing, and transepithelial egression) of allergic inflammatory cells recruited to the lungs under normal conditions (top) or in the absence of MMPs (bottom). Cellular migration is shown progressing from right to left, with recently extravasated cells (including T cells, monocytes, eosinophils, and mast cells) traversing the pulmonary interstitium and the airway epithelium to enter the airway lumen, where they are cleared in the wild-type (WT) mice (top) and less so in MMP null mice (bottom). Interstitial inflammatory cells are recruited to the lumen by establishing a transepithelial chemotactic gradient in which chemokines (CCL) are strongly expressed in the lumen and on the apical surface of epithelial cells relative to the interstitium. Lack of MMPs disrupts the formation of this chemokine gradient and impairs migration of cells at the points marked “X”.