Tyrosine kinase blockers inhibit Fas receptor-mediated apoptosis in mouse eosinophils in vitro and in vivo. (A) Freshly purified BAL eosinophils were preincubated with lavendustin (16 μg/mL) or genistein (20 μg/mL) and then stimulated with anti-Fas MoAb for 24 hours. Both blockers significantly inhibited Fas receptor-mediated death. Data are from a total of 45 animals. *P < .05. (B) OA-immunized mice were challenged with antigen to cause lung eosinophilia. The lungs of these mice were pretreated with tyrosine kinase blocker for 1 hour and then with anti-Fas MoAb via the intranasal route. BAL was performed 24 hours later, and the numbers of eosinophils were determined. Anti-Fas MoAb-treated mice demonstrated significantly reduced BAL eosinophils. This treatment had no significant effect on BAL eosinophil numbers when mice were pretreated with lavendustin A. *P < .05; **P < .01. (C) Examples for BAL cytology showing disappearance of eosinophils as a consequence of anti-Fas MoAb treatment and abrogation of this effect by lavendustin A. Data are from 6 to 8 animals per condition.