(A) Effect of the synthetic peptide GRGDSP on adhesion of CFU-E to the CBD fragment of FN. Bone marrow cells were incubated in wells coated with CBD in the presence of the indicated concentrations of GRGDSP (•) or GRGESP (○) peptides. (B) Effect of integrin β₁ subunit antibody on adhesion of CFU-E to FN and the CBD fragment of FN. Bone marrow cells were incubated in wells coated with FN or CBD in the absence of antibody (□), or in the presence of 100 μg/mL nonimmune rabbit IgG (▨), or 100 μg/mL β₁ subunit antibody (▪). For both (A) and (B), the nonadherent and adherent populations of cells were then assayed for CFU-E and results are expressed as the mean percent cell adhesion ± SEM (n = 3), *P ≤ .02.