Identification of novel B-cell neutralizing epitopes in goose Astrovirus type 2

Since 2015, outbreaks of goose Astrovirus type 2 (GAstV-2) have caused significant economic losses in the goose industry by inducing severe visceral and articular gout in goslings, with mortality rates reaching up to 50 %. The capsid (Cap) protein of GAstV-2 is the primary structural protein that elicits immune responses, but it has not been extensively studied for neutralizing epitopes or infection mechanisms. In this study, two novel neutralizing monoclonal antibodies (mAbs) 4A7 and 8H3 were generated, which specifically target the Cap protein and effectively inhibit GAstV-2 infection in vitro. Epitope mapping using alanine-scanning mutagenesis revealed that the epitopes recognized by mAbs 4A7 and 8H3 are located within the amino acids sequences ⁴⁴³ESCSFLVF⁴⁵⁰ and ⁴²⁵QVTPSLVYNF⁴³⁴ of the Cap protein, respectively. These two epitopes are highly conserved among GAstV-2 strains, but show substantial divergence from GAstV-1 strains. Structural analysis indicated that these epitopes are situated on the surface of the Cap protein, within the P2 domain, which is critical for virus-receptor interactions and immune recognition. The findings not only identify novel neutralizing epitopes in GAstV-2 but also highlight the potential of mAbs 4A7 and 8H3 for developing epitope-based vaccines and diagnostic assays.