CD11c/CD18 transfectants show specific cation-dependent binding to coated ICAM-4Fc. (A) The adhesion of parental L cells and CD11c/CD18 transfectants to ICAM-4Fc and human IgG proteins coated on plastic wells. CD11c/CD18 L cells + ICAM-4Fc (▪), parental L cells + ICAM-4Fc (▴), CD11c/CD18 L cells + human IgG (○), parental L cells + human IgG (◊). (B) The effects of anti–ICAM-4, anti-CD18, and anti-CD11c mAbs on adhesion of CD11c/CD18 transfectants to 0.5 μmg purified ICAM-4Fc fusion protein. Controls included wells with binding of wild-type L cells (not shown) and the effect of control antibody (anti-CD11a mAb). (C) The binding of transfectants to ICAM-4Fc in the absence or presence of divalent cations. (D) The binding of CD11c/CD18 transfectants to coated ICAM-4Fc in the presence of indicated concentrations of soluble wild-type CD11c I domain (▪) and the active mutant I domain (○). In panels A and B the results are shown as the percentage of input cells bound ± SD. In panels C and D the results are expressed as a relative percentage of bound cells, where 100% is given as the number of cells bound to the ICAM-4Fc in the presence of divalent cations (C) or in the absence of soluble I domain (D). Background binding of cells to HSA was subtracted. The experiments were repeated 3 to 5 times with similar results. Standard deviations and statistical significances are shown; ***P < .001, **P < .01.