CD19 and colorectal carcinoma: Flow cytometry analysis revealed that IL-21 was mostly produced by CD3+CD8− T cells (Figure 1B) and minimally expressed by CD3+CD8+ T cells and natural killer (NK) T cells (CD3+CD56+ cells) (2.54±0.4 and 0.96±0.28 respectively); no IL-21 staining was seen in NK cells (CD3-CD56+ cells), macrophages (CD68+ cells) and B cells (CD19+ cells) thus ruling out such cells as sources of IL-21 in human CRC (Figure 1B).