Moreover, in the present study, PD-1 expression was substantially upregulated in the effector memory CD8+ T cells of ABC-fed B*57:01-Tg mice as well as their CD4+ T cell-depleted counterparts (Fig. 2); this might suppress the induction of skin rash often associated with clinical AHS. This evidence concerns the gene PDCD1 and mitochondrial DNA depletion syndrome 4a.