α₂β₁ Integrin–dependent adhesion to immune complexes. (A) PMCs (2000 cells/well) isolated from wild-type (WT) and α₂-null (KO) mice were assayed for adhesion to a matrix consisting of Listeria alone, Listeria plus anti-Listeria antibody, Listeria, anti-Listeria antibody and 100% mouse serum, BSA alone, BSA plus anti-BSA antibody, BSA plus anti-BSA antibody and 100% mouse serum, type 1 collagen, or fibronectin for 1 hour. (B) PMCs isolated from WT and KO mice were assayed for adhesion to a matrix consisting of Listeria, anti-Listeria antibody, and increasing concentrations of mouse serum. (C) PMCs from WT mice were assayed for adhesion to a matrix consisting of BSA and anti-BSA antibody alone, with no mouse serum (0%), or BSA and anti-BSA antibody plus 50% mouse serum either untreated (Untreated) or heat treated at 56°C for 30 minutes (Heat treated). (D, E) PMCs from WT and KO mice were assayed for adhesion to a matrix consisting of Listeria and anti-Listeria antibody alone (Control), or Listeria, anti-Listeria antibody and 50% murine serum, 50% human serum, 50% human serum depleted of C2 complement component (C2-dep), or 50% serum from C1q-deficient (C1q^-/-) mice, or to type 1 collagen or fibronectin. All experiments were carried out in the presence of 2 mM MgCl₂. All results are presented as mean ± SEM from triplicate wells of a single experiment and represent 1 of at least 3 experiments demonstrating similar results.