Phosphotyrosine Phosphotyrosine Phosphotyrosine IL-5 IL-5 IL-4 IL-6 IL-10 Fas FasL IL-2 IL-2R Phosphotyrosine Phosphotyrosine Phosphotyrosine CD40L CD40 IgE IgE TCR CD3 Ig MHC CD23 BCR NFAT Signaling and Lymphocyte Interactions