Constitutive activation of JAK2 in patient DLBCL tumors (n = 12) and cell lines. (A) IHC detection (400× magnification) of activated JAK2 protein in DLBCL tissue. (B) IHC detection of activated JAK2 in DLBCL cell lines. (C) Phosphorylation levels of JAK2 in human DLBCL cell lines (ABC and GCB) were analyzed by Western blotting. CD19⁺ B cells were used as a control. (D) JAK2 mRNA expression was analyzed in DLBCL lines by RT-PCR.