Identification of two neutralization epitopes on the capsid protein of avian hepatitis E virus.

Avian hepatitis E virus (avian HEV) is genetically and antigenically related to human HEV, the causative agent of hepatitis E. To identify the neutralizing epitopes on the capsid (ORF2) protein of avian HEV, four mAbs (7B2, 1E11, 10A2 and 5G10) against recombinant avian HEV ORF2 protein were generated. mAbs 7B2, 1E11 and 10A2 blocked each other for binding to avian HEV ORF2 protein in a competitive ELISA, whereas 5G10 did not block the other mAbs, suggesting that 7B2, 1E11 and 10A2 recognize the same or overlapping epitopes and 5G10 recognizes a different one. The epitopes recognized by 7B2, 1E11 and 10A2, and by 5G10 were mapped by Western blotting between aa 513 and 570, and between aa 476 and 513, respectively. mAbs 1E11, 10A2 and 5G10 were shown to bind to avian HEV particles in vitro, although only 5G10 reacted to viral antigens in transfected LMH cells. To assess the neutralizing activities of the mAbs, avian HEV was incubated in vitro with each mAb before inoculation into specific-pathogen-free chickens. Both viraemia and faecal virus shedding were delayed in chickens inoculated with the mixtures of avian HEV and 1E11, 10A2 or 5G10, suggesting that these three mAbs partially neutralize avian HEV.