The heparan sulfate proteoglycan form of epithelial CD44v3 serves as a CD11b/CD18 counter-receptor during polymorphonuclear leukocyte transepithelial migration.

Leukocyte beta2-integrin CD11b/CD18 mediates the firm adhesion and subsequent transepithelial migration of polymorphonuclear leukocytes, but the identity of its counter-receptor(s) on epithelia remains elusive. Here we identified a monoclonal antibody, clone C3H7, which strongly bound to the basolateral membranes of epithelial cells and inhibited both the adhesion of epithelial cells to immobilized CD11b/CD8 and the transepithelial migration of PMNs in a physiologically relevant basolateral-to-apical direction. C3H7 antigen expression in epithelial monolayers was significantly increased by treatment with proinflammatory cytokine interferon-gamma or a combination of interferon-gamma and tumor necrosis factor-alpha. Up-regulation of C3H7 antigen was also observed in the epithelium of inflamed human colon tissues. Microsequencing and Western blotting of the purified antigen showed it to be CD44 variant 3 (CD44v3), a approximately 160-kDa membrane glycoprotein. Further studies demonstrated that this epithelial CD44v3 specifically binds to CD11b/CD18 through its heparan sulfate moieties. In summary, our study demonstrates for the first time that the heparan sulfate proteoglycan form of epithelial CD44v3 plays a critical role in facilitating PMN recruitment during inflammatory episodes via directly binding to CD11b/CD18.