In this work to clarify the role of prostaglandin D2 (PGD2) in liver pathophysiology, we found that mice deficient in PGD receptor DP1 showed exacerbated hepatitis after ConA injection, whereas administration of a DP1-specific agonist BW245C significantly suppressed liver inflammation induced by ConA. The gene discussed is PTGDR; the disease is hepatitis A virus infection.