CD43 (sialophorin, leukosialin) shedding is an initial event during neutrophil migration, which could be closely related to the spreading of adherent cells

Leukosialin is a negatively-charged mucin-like membrane protein of leukocytes. This anti-adhesive molecule prevents uncontrolled cellular interactions and is proteolytically cleaved during neutrophil activation. CD43 is shed in vivo during neutrophil migration to the inflammatory site. We have analysed the decrease in CD43 expression during in vitro adherence of TNF-alpha activated PMN. CD43 was quantitated by flow cytometry on TNF-alpha-activated PMN either maintained in suspension or allowed to adhere then detached with EDTA. Although TNF did not induce significant modification of CD43 expression on suspended cells, we showed that 40% of membrane CD43 is released during neutrophil TNF-induced adhesion to serum-coated plates or endothelial cells, and that migration through the endothelial monolayer did not result in further shedding. Adhesion-blocking anti-beta 2 integrin mAbs prevented CD43 shedding. beta 2 integrin "activation" by anti-CD18 mAbs or Mn ions did not decrease CD43 expression if adhesion was prevented by stirring. Inhibitors of signal transduction or of cytoskeleton association, which allowed cells to adhere but not to spread, inhibited the shedding of CD43 during adhesion. We conclude that CD43 shedding is not promoted by beta 2 integrins engagement or adhesion but is concomitant with spreading of adherent cells.