Effects of DN-JAK1 and in DN-JAK2 on IL-5 signal. (A) hIL-5Rα and βc cDNA were transfected into COS7 cells together with either a vector control, a kinase-negative form of JAK1, or a kinase-negative form of JAK2. After incubation for 36 hours, cells were harvested and lysed after IL-5 stimulation. Immunoprecipitation was performed with anti-JAK1 or -JAK2 Ab. After separation on SDS-PAGE, the transferred membranes were immunoblotted with antiphosphotyrosine MoAb and reprobed with the relevant Ab. (B) Immunoprecipitation with anti-βc MoAb was also performed. After separation on SDS-PAGE, the proteins were probed with antiphosphotyrosine MoAb and reprobed with anti-βc polyclonal Ab.