In addition, we found that whereas inhibitory receptor CTLA-4 expression is conserved (Figure S4A in Text S1), PD-1 expression is up-regulated on total CD8+ T cells (p = 0.005 and 0.008 for inactive and active SLE, respectively) compared to healthy controls (Figure S4B in Text S1). Here, CD8A is linked to systemic lupus erythematosus.