Adhesion of murine WT and FcRγ^−/− washed platelets to Toolkit-III peptides. (A) The response is given as absorbance at 405 nm (mean ± SE: n = 10). For control platelets, adhesion was observed to the following substrates (in decreasing order of magnitude): CRP (in 10/10 experiments); III-30 (10/10); III-04 (10/10); III-31 (10/10); GFOGER (10/10); III-15 (9/10). (B) Effect of inhibitors of integrins α2β1 and αIIbβ3 on adhesion of murine platelets to Toolkit peptides III-04, III-30, and III-31. The anti-α2 antibody Ha1/29 (2 μg/mL) abolished binding to the α2β1 ligand GFOGER as well as III-04 and III-31, whereas it had no effect on either CRP or III-30. The αIIbβ3 antagonist lotrafiban (LOT: 10 μM) partially inhibited adhesion of platelets to all ligands, indicating a general role for platelet cross-linking by integrin in promoting adhesion (mean ± SE: n = 2).