Previous studies showed that adoptive cell transfer of lymph node cells isolated from scurfy mice into Rag-1 KO mice induced systemic inflammation resembling the phenotype of scurfy mice, that cell transfer of neonatal thymectomy (NTx)-PD-1 KO mice into Rag-2 KO mice induced hepatitis and that adoptive cell transfer of Th1 cells into Rag-2 KO mice induced colitis, and such inflammation was suppressed by co-transfer of FoxP3+ Tregs37–42. Here, PDCD1 is linked to hepatitis A virus infection.