Adhesion of LFA-1 transfectants. Adhesion of LFA-1 (CD11a/CD18) transfectants to ICAM-1 (A), ICAM-2 (B), and ICAM-3 (C). Adhesion was done in the absence of activating agents, in the presence of 1.5 mM EGTA and 5 mM MgCl2 (Mg/EGTA), or with the activating monoclonal antibody KIM185 (2.5 μg/mL) or with both Mg/EGTA and KIM185 (for ICAM-2 and ICAM-3 only). CD18-independent adhesion (background) was determined by inhibition with monoclonal antibody 1B4 (10 μg/mL) and has been subtracted.