ENHANCED ICAM-1-DEPENDENT ADHESION OF MYELOMONOCYTIC CELLS EXPRESSINGINCREASED LEVELS OF BETA(2)-INTEGRINS AND CD43

Interaction of ICAM-1 and its ligands plays an important role in the l eukocyte binding to endothelium. The best characterized ICAM-ligands b elong to the family of beta(2)-integrins (CD11/CD18), but recently it has been suggested that CD43, a molecule with no structural resemblanc e to integrins binds ICAM-1 also. On the leukocytes the main regulator y pathway for ICAM-mediated binding is believed to be a short-term reg ulation of the avidity of CD11/CD18. In this study the authors investi gated whether a quantitative increase in the surface expression of ICA M-ligands also can lead to enhanced binding to purified ICAM-1. PMA-tr eatment differentiates myelomonocytic cell lines into macrophages with a concomitant increase in the surface expression and mRNA-levels of t he beta(2)-integrin alpha- and beta-chains as well as that of CD43, an other ICAM-ligand. The binding of the PMA-treated THP-1 cells to ICAM- 1 was increased simultaneously compared to non-treated cells. The bind ing was blocked completely with antibodies to CD18 and ICAM-1. It is c oncluded that in addition to the transient qualitative regulation, a l ong-term quantitative regulation of ICAM-1 ligands also plays a role i n increasing the adhesiveness of myelomonocytic cells. This may be rel evant in chronic inflammation episodes.