Effects of specific blockade of IL-9 on Jak3, Stat3, and ALK. (A) Western blot studies show that increasing concentrations of anti–IL-9–neutralizing antibody (80 and 160 μg/mL) decreases pJak3 in the 3 ALK⁺ ALCL-cell lines. The decrease in pStat3 levels in SU-DHL-1 and SUP-M2 cells was more pronounced at a concentration of 160 μg/mL. Despite the slight increase in pStat3 levels in Karpas 299 cells at a concentration of 80 μg/mL, it decreased to the baseline level at 160 μg/mL. Total levels of Jak3 and Stat3 were not affected. β-Actin confirmed equal loading of the proteins. The experiment was performed 3 times with consistent results. (B) Western blot studies did not demonstrate similar changes in pJak3, Jak3, pStat3, and Stat3 levels after treating the negative control cells HT29 with similar concentrations of the anti–IL-9–neutralizing antibody. β-Actin confirmed equal loading of the proteins. (C) After treating the ALK⁺ ALCL-cell lines with anti–IL-9–neutralizing antibody (160 μg/mL), tyrosine kinase activity of Jak3 and ALK were measured. Normalized data reveal reduction to 60% or less of the control levels of the kinase activity of the 2 enzymes. Control cells were treated with IgG. Shown are averaged data of 2 consistent experiments.