Tyrosine kinase blockers inhibit Fas receptor-mediated apoptosis in human eosinophils. (A) (Left panel) Freshly isolated eosinophils were preincubated with lavendustin A (16 μg/mL), genistein (20 μg/mL), or herbimycin A (4 μg/mL) and then stimulated with anti-Fas MoAb for 30 hours. Lavendustin A completely, and the other two kinase blockers partially, abrogated Fas receptor-mediated eosinophil death. *P < .05; **P < .01. (Right panel) Dose-dependent effect of lavendustin A in a time course experiment. (B) Fas receptor-mediated cell death in human eosinophils is due to apoptosis. Untreated or lavendustin A-pretreated eosinophils were stimulated with anti-Fas MoAb. Cells were stained with Giemsa-May-Grünwald (Diff-Quik). Apoptotic eosinophils are characterized by reduced cell volume as well as nuclear condensation and fragmentation. The lavendustin A-pretreated cell populations demonstrated less apoptosis. Data are from six independent experiments.