Autocrine release of IL-9 by ALK⁺ ALCL cells. Western blot studies show the presence of IL-9 protein in cell lysates from Karpas 299, SU-DHL-1, and SUP-M2 cells. Anti–IL-9–neutralizing antibody had no significant effect on IL-9 levels in the cell lysates. β-Actin shows equal loading of the proteins. Also, these studies show the presence of IL-9 in the culture medium from the same cells after being maintained in FBS-free medium for 12 hours. The anti–IL-9–neutralizing antibody (80 μg/mL) effectively bound to IL-9, as demonstrated by the lack of IL-9 in the culture medium after protein complexes were eluted. The negative control cells HT29 demonstrate lack of IL-9 in the cell lysate and the cell-culture medium. The experiment was repeated 2 times with consistent results.