The percentages of IL-21-producing PD-1+CD4+ T-cells were also not significantly different in active SLE patients as compared to inactive SLE patients (14.5 ± 8.0% vs. 12.11 ± 11.6%; p = 0.30) and as compared to HC (14.5 ± 8.0% vs. 14.7 ± 16.2%; p = 0.53). Here, PDCD1 is linked to systemic lupus erythematosus.