The expression of CXCR5, PD-1 and ICOS on CD8+ T cells in polyp tissues was significantly increased compared with control tissues (P < 0.01, Fig. 3), and some IL-21-expressing CD8+ T cells were found to co-express CXCR5, ICOS and PD-1 in polyp tissues. Here, CXCR5 is linked to polyp.