DOWN-REGULATION BY TUMOR-NECROSIS-FACTOR-ALPHA OF NEUTROPHIL CELL-SURFACE EXPRESSION OF THE SIALOPHORIN CD43 AND THE HYALURONATE RECEPTOR CD44 THROUGH A PROTEOLYTIC MECHANISM

Adhesion of human neutrophils to endothelial cells is a crucial step during migration to the extravascular sites of inflammation. A large number of molecules, including the CD44 and LAM-1 antigens, have been described to participate in this process. We have investigated the regulation by human recombinant tumor necrosis factor-alpha (TNF-alpha) of human neutrophil plasma membrane expression of both CD44 and LAM-1 adhesion molecules, as well as that of CD43 sialophorin, which has been involved in adhesion and activation of leukocytes. The expression of these three antigens was down-regulated in neutrophils upon TNF-alpha treatment, as determined by immunofluorescence and immunoprecipitation experiments. However, the expression of other cell surface molecules, such as CD45 or CD11b, was up-regulated. Similar regulatory effects were also observed upon neutrophil treatment with other activating agents such as the chemoattractant peptide formyl-Met-Leu-Phe, the calcium inophore A23187, or the phorbol ester phorbol 12-myristate 13-acetate. Protease inhibitors virtually abrogated the TNF-alpha-induced down-regulation of CD43 and CD44 expression, but not that of LAM-1, suggesting the involvement of a protease activity in this process. These results underline the role of TNF-alpha on the differential regulation of cell surface expression of neutrophil adhesion molecules, thus implying modifications in the neutrophil adhesive properties.