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

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Abstract
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.