ALK⁺ ALCL-cell lines express IL-9. (A) RT-PCR studies demonstrate the presence of IL-9 mRNA in ALK⁺ ALCL cells. L1236 and HT29 cells were used as positive and negative controls, respectively. β-Actin demonstrates equal loading. (B) Immunohistochemical staining of the ALK⁺ ALCL-cell lines confirmed the expression of IL-9. L1236 and HT29 were used as positive and negative controls, respectively (original magnification × 200). (C) Confocal microscopy and immunofluorescence staining using specific antibody (bottom panel) or IgG (top panel) show the expression of IL-9 in ALK⁺ ALCL-cell lines (original magnification × 600).