PARP9 and systemic lupus erythematosus: We found that the nicotinate/nicotinamide metabolic pathway showed the highest correlation (r2 = 0.6562; P ≤ 0.0001, Pearson’s correlation coefficient) (Fig. 6a) and NAD-consuming enzymes, such as the poly(ADP-ribose) polymerases (PARP9, PARP10, and PARP12) and CD3828, were markedly upregulated in CD8+ T cells from IFN-High SLE patients (Fig. 6b).