α2E318A and α2GFFKRΔ mutant integrins confer binding to immobilized and soluble collagen. (A) Surface expression of α2 integrins in RBL-2H3 cells infected with lentiviral vectors encoding wild-type (WT), E318A, and GFFKRΔ α2 integrin subunits. Cells were sorted to obtain populations with similar expression levels. (B) Static adhesion of RBL-2H3 cells expressing empty vector or the indicated α2 integrins to immobilized type I collagen in the presence and absence of 5 mM EDTA. N = 3; mean and SD are shown. *P < .05 compared with α2WT. (C) Activated α2 mutants confer soluble collagen binding. Binding of FITC-conjugated soluble collagen to RBL-2H3 cells expressing wild-type, E318A, or GFFKRΔ α2 subunits was measured using flow cytometry. (D) Quantitation of soluble collagen binding conferred by the E318A and GFFKRΔ α2 integrin mutants. N = 7; mean and SD are shown. *P < .05 compared with α2WT.