The effect of antibodies to the integrin α₂β₁ on tyrosine phosphorylation. (A) Platelets were stimulated with (i) collagen (30 μg/mL) or (ii) CRP (3 μg/mL) for 90 seconds in the presence of MoAb 6F1 (1 to 100 μg/mL) and subsequently analyzed by immunoblotting using the antiphosphotyrosine MoAb 4G10 as described in the Materials and Methods. MoAb 6F1 was administered 5 minutes before the agonist. ECL exposures from collagen-stimulated platelets were exposed for a longer period than that from CRP-stimulated cells, as indicated by the greater number of bands in the basal lane. The location of the heavy chain of MoAb 6F1 (IgG) is indicated by the arrow. (B) Tyrosine phosphorylation of syk and PLCγ2 in the presence of antibodies to the integrin α₂β₁ . Samples were immunoprecipitated using antibodies to (i) syk and (ii) PLCγ2 as described in the Materials and Methods before immunoblotting with MoAb 4G10. Samples were incubated with MoAb 6F1 (30 μg/mL) or MoAb 13 (5 μg/mL) for 5 minutes before the addition of agonist. Results are representative of two experiments.