P-selectin and CD11b/CD18 are both required for platelet-induced protein-tyrosine phosphorylation in PMN. (A) PMN were coincubated with thrombin-activated platelets in standard conditions in the absence or in the presence of 1 mmol/L Ca²⁺ and Mg²⁺ alone or together. The reaction was stopped at 2 minutes and samples processed for protein-tyrosine phosphorylation. The figure shows the Western blot of samples from a representative of two different experiments. (B) PMN and thrombin-activated platelets were preincubated for 15 minutes with the corresponding antibodies. Mixed-cell suspensions were coincubated in standard conditions, the reaction stopped at 2 minutes, and samples processed for analysis of protein-tyrosine phosphorylation. The figure shows the Western blot of samples from a representative experiment and bars report the optical density of the tyrosine-phosphorylated P∼110. Values are means ± SEM, n = 3 or 4.