Adhesion of hemopoietic cells to ICAM4Fc is α₄β₁-mediated, and adhesion to nonhemopoietic cells is α_V integrin–mediated.

Adhesion assays were as described in “Materials and methods.” (A) Adhesion of cation-activated, hemopoietic, HEL cells to ICAM4Fc in the presence of blocking (^b) or activating (^a) antibodies to integrin α or β subunits as described in “Materials and methods.” Results are cells bound ± SD (n = 6), in comparison with control antibody (C, 100%). Antibodies used were β₁^b, clone 13; β₁^a, TS2/16; β₂^b, MHM23; β₃^b, RUU-PL; α₁, FB12; α₂, JA218; α₃, C3(VLA3); α₄^b, HP2/1; α₄^a, 44H6; α₅^b, SNAKA55; α₆^b, NKI-GoH3; and α_V ^b, 69.9.5. ICAM4Fc was coated at 0.5 μg/well. (B) Comparison of the relative avidity of adhesion of cation-activated HEL cells to VCAMFc (diamonds), MAdCAMFc (triangles), ICAM4Fc (squares), and NCAMFc (crosses) by titration of CAMFc protein as described in “Materials and methods.” Results are input cells bound ± SD (n = 6). (C) Adhesion of cation-activated β₁-negative JY cells and HEL cells to VCAMFc, MAdCAMFc, ICAM4FcFc, and NCAMFc. Fc fusion proteins were coated at 0.05 μg/well (VCAMFc, MAdCAMFc) and 1 μg/well (ICAM4Fc, NCAMFc). Results are the percentage of input cells bound ± SD (n = 6). (D) Adhesion of PMA+ cation–activated, nonhemopoietic, FLY cells to ICAM4Fc in the presence of blocking antibodies to integrin α or β subunits or integrin complexes as described in “Materials and methods.” Results are cells bound ± SD (n = 6), in comparison with control antibody (C, 100%). Blocking antibodies were as above except β₄, ASC-3; α_Vβ₃, LM609; and α_Vβ₅, P1F6. ICAM4Fc was coated at 0.25 μg/well.