Oligomerization of the αC domains stimulates RGD-dependent adhesion of endothelial cells via αVβ3, αVβ5, and α5β1 integrins. Quantitative adhesion assays were performed with 5 × 10⁴ HUVECs plated in serum-free DMEM for 20 minutes at 37°C on plastic wells coated with 20 μg/mL αC monomers, αC(FXIII) oligomers, or αC(tTG) oligomers. (A) Effects of oligomerization and RGD-containing peptide on cell adhesion to the αC domain species (□, αC monomers; ▪, αC(FXIII); ▦, αC(tTG)). Cells were plated without treatment or in the presence of 250 μg/mL GRGDSP or control GRGESP peptides. The number of untreated adherent cells on αC monomers was taken as 100%. (B) The role of individual integrins in adhesion to αC monomers and oligomers. Cells were plated without treatment or in the presence of 20 μg/mL blocking antibodies to α5β1 (mAb P1D6; ▨), αVβ5 (mAb P1F6; ▦), or αVβ3 (mAb LM609; ▪). The numbers of untreated cells (□) adherent to αC monomers or αC(FXIII) oligomers were taken as 100%. The results shown in both panels are the means ± standard deviations of 3 independent experiments performed in duplicates.