Activated platelets induce protein-tyrosine phosphorylation in PMN. PFA-fixed thrombin-activated platelets alone (P-activated), PMN alone or combined with PFA-fixed resting (P-resting), or thrombin-activated (P-activated) platelets at a ratio of 1:5 were incubated for different times at 37°C and stirring at 1,000 rpm (standard conditions). In parallel experiments PMN were challenged with fMLP (1 μmol/L) for comparison. The figure shows the Western blot of samples from a representative experiment and the graph reports the optical density (in arbitrary units) of the major tyrosine-phosphorylated protein showing a relative molecular mass between 97 and 116 kD (P∼110) in the corresponding samples (symbols in brackets). Values are means ± SEM, n = 3.