Antiphosphotyrosine Western blot of anti-hβc immunoprecipitate from FDC-P1 cells expressing IL-3Rα + hβc, IL-3RΔNT + hβc, or IL-3RΔCT + hβc, with (+) and without (-) stimulation by 15 nmol/L hIL-3. Cells were cultured for 18 hours in the presence or absence of hIL-3 and the hβc immunoprecipitated with MoAb 4F3. Phosphoprotein in the immunoprecipitate was detected by Western blotting using antiphosphotyrosine MoAb 3-365-10 (Boehringer Mannheim).