Effect of PMA on the stimulation of the tyrosine phosphorylation of Jak2 induced by GM-CSF in human neutrophils . The cells were simultaneously treated with BSA (0.01%), GM-CSF (4 nmol/L), and/or phorbol esters (90 nmol/L) for 15 minutes at 37°C. Neutrophils were lysed under denaturing conditions and the immunoprecipitation was performed using anti-Jak2 antibodies. The level of tyrosine phosphorylation was revealed by blotting with anti-p85 antibodies. The data illustrated are representative of similar results obtained in four other independent experiments. Ip, immunoprecipitation; wb, Western blot.