CD40 and rheumatoid arthritis: As shown in Figure 4d, inclusion of rIL-21 led to higher expressions of CD25, CD69 and CD40 in RA patients and this response was reversed by anti-IL-21R antibodies (CD25: 43.48% ± 2.63% vs. 61.63% ± 2.63% vs. 57.74% ± 2.89%, P < 0.05; CD69: 1.48% ± 0.26% vs. 2.85% ± 0.43% vs. 2.30% ± 0.48%, P < 0.05; CD40: 73.14% ± 1.09% vs. 81.77% ± 1.77% vs. 75.22% ± 1.64%, P < 0.05; Figure 4d).