Upon examination of the effects of melanoma-derived PAEP on the activation of purified CD4+ T helper cells, the secretion of IL-2 and IFN-γ, but not IL-4 and IL-5significantly decreased with the addition of PAEP-rich supernatant, indicating that the activation of Th1 cells was inhibited by melanoma-derived PAEP. This evidence concerns the gene IL4 and melanoma.