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

Pertussis toxin (PTX) has been shown previously to promote myelomonocytic c ell adhesion in serum. The aim of the present study was to identify, using transforming growth factor-beta(1) and 1,25(OH)(2) vitamin D-3 (TGF-beta(1) /D-3)-primed U937 cells, the PTX-binding site(s) and the adhesion molecule( s) responsible for PTX-induced myelomonocytic cell adhesion. Monoclonal ant ibodies (mAbs) directed against CD14, CD11b, CD18 or urokinase receptor (uP AR) 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 plat es and significantly inhibited a PTX-induced rise of [Ca2+](i) in primed U9 37 cells. A. receptor-isolation study showed that biotinylated PTX recogniz ed a 48 000-molecular weight protein in primed U937 cell lysates, which cou ld be specifically blocked by excess unlabelled PTX or by anti-CD14 mAb. On the other hand, mAb directed against uPAR significantly blocked PTX-induce d myeloid cell adhesion to serum and to immobilized vitronectin, a major ex tracellular 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 pathogenet ic mechanism for the respiratory tract infection induced by Bordetella pert ussis.