TLR9 and hepatitis A virus infection: Endolysosomal exonucleases, phospholipase D3 (PLD3), and PLD4 (type II transmembrane proteins) degrade TLR9, and their genetic deficiency causes an enhanced TLR9 expression and TLR9-dependent severe inflammation (lethal hepatitis), causing the death of newborns within two to three weeks after birth (219).