JAK3-AV confers enhanced proliferative capacities. (A) ³H-thymidine incorporation after 60 hours of stimulation with PMA/ionomycin of purified CD8⁺ T cells from JAK3-WT (■) and JAK3-AV (□) mice. Rightmost bars show effect of pharmacologic inhibition of JAK3 with JAK inhibitor I (JAK-I). Bar graphs represent the average and standard deviation of 3 independent experiments performed in triplicate. (B) Assessment of phosphorylation status of downstream effectors of JAK3 by intracellular staining of JAK3-WT (shaded histogram) and JAK3-AV (open histogram) splenocytes with phosphospecific antibodies. Histograms display a representative experiment gated on CD8⁺ T cells (n = 6). Bar graphs represent the average and standard deviation of 3 independent experiments for each phosphoprotein. (C) Western blot from bone marrow lysates from JAK3-WT or JAK3-AV animals shows constitutive phosphorylation of JAK3 downstream targets in the latter. The last lane shows inhibition of phosphorylation by JAK-I.