α₂β₁ Integrin–dependent adhesion to C1q. (A) PMCs from WT and KO mice either were untreated or were stimulated with PDB (40 nM) and assayed for adhesion to C1q, type 1 collagen, fibronectin, or BSA, as indicated. (B, C) Adhesion of NMuMG-1 cells that express endogenous murine α₂β₁ integrin (NMuMG-1), α₂β₁ integrin-negative NMuMG-3 cells (NMuMG-3), α₂β₁ integrin-negative K562 cells transfected with either control vector (K562-Control) or human full-length α₂β₁ integrin cDNA(K562-X2C2) to C1q, type 1 collagen, fibronectin, or BSA was analyzed. 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.