antigen 1 (CD1 1a/CD1 8) and Mac-i (CDi i b/CD1 8) for binding to intercellular adhesion molecule-i (CD54)

Both human integrin receptors Mac-i (CD! ib/CD18, CR3) and lymphocyte function-asso- ciated antigen (LFA)-i (CDiia/CDi8) have been demonstrated to bind human intercellular adhesion molecule-i (ICAM-i) (CD54). Here we show that LFA-1 and Mac-i can bind to ICAM-i in the mouse as well. Interestingly, we observed that binding of murme LFA-1 dominates over Mac-i for binding to ICAM- i . Using three different murine macrophage cell lines that express distinct levels of LFA-i and Mac-i on their cell surface, we could only detect Mac-i-dependent adhesion to ICAM-i when little or no LFA-i is expressed on the cell surface. When LFA-i and Mac-i are expressed at similar levels, the LFA- i/ICAM- i interaction dominates over Mac- i/ICAM-i interaction, indicating that there is a corn- petition of LFA-1 and Mac-i for ICAM-i binding. J. Leukoc. Biol. 59: 648-655; i996.