Because others and our studies (data not shown) had found that IL-12 levels were significantly increased in polyp tissues compared with control sinonasal tissues, and IL-12 was previously found to induce the generation of IL-21 and IFN-γ co-expression by CD4+ T cells15, we evaluated whether IL-21-producing CD8+ T cells in NP tissues were regulated by IL-12. Here, CD4 is linked to polyp.