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Mechanisms of pertussis toxin‐induced myelomonocytic cell adhesion: role of CD14 and urokinase receptor

Pertussis toxin (PTX) has been shown previously to promote myelomonocytic cell adhesion in serum. The aim of the present study was to identify, using transforming growth factor‐β1 and 1,25‐(OH)2 vitamin D3 (TGF‐β1/D3)‐primed U937 cells, the PTX‐binding site(s) and the adhesion molecule(s) responsible for PTX‐induced myelomonocytic cell adhesion. Monoclonal antibodies (mAbs) directed against CD14, CD11b, CD18 or urokinase receptor (uPAR) significantly inhibited PTX‐induced primed U937 cell adhesion in serum in a concentration‐dependent manner. However, only anti‐CD14 and anti‐CD18 mAbs were able to prevent the myeloid cells from binding to PTX‐coated plates and significantly inhibited a PTX‐induced rise of [Ca2+]i in primed U937 cells. A receptor‐isolation study showed that biotinylated PTX recognized a 48 000‐molecular weight protein in primed U937 cell lysates, which could be specifically blocked by excess unlabelled PTX or by anti‐CD14 mAb. On the other hand, mAb directed against uPAR significantly blocked PTX‐induced myeloid cell adhesion to serum and to immobilized vitronectin, a major extracellular matrix protein in serum. Taken together, our data suggest that PTX may bind to cell‐surface CD14 to induce myelomonocytic cell adhesion to vitronectin in serum via uPAR activation, which may represent a pathogenetic mechanism for the respiratory tract infection induced by Bordetella pertussis.