IRF4 is highly expressed in ALCL. (A) Immunohistochemical IRF4 staining of an IRF4-positive ALCL case (left) with internal negative controls (tumor-infiltrating macrophages and endothelia), and an IRF4-negative ALCL case (right) (original magnification ×320). (B) IRF4 mRNA is highly expressed in ALCL compared with the SS cell line HuT 78 and T-ALL cell lines as measured by quantitative PCR. IRF4 mRNA levels were normalized to expression of GAPDH. Error bars indicate standard deviation. (C) Western blot analysis of IRF4 expression in MM, ALCL, SS, and T-ALL cell lines. Five of 6 ALCL cell lines have high IRF4 protein expression.