# Analysis of MHC class II-bound CyHV-2 peptides in Carassius gibelio using mass spectrometry

## TL;DR

This study identifies peptides from CyHV-2 virus presented by MHC-II molecules in crucian carp, offering insights for developing vaccines against this aquatic pathogen.

## Contribution

The study provides the first comprehensive antigenic profile of CyHV-2 peptides presented by MHC-II in Carassius gibelio using immunopeptidomics.

## Key findings

- 276 antigenic peptides from 39 viral proteins were identified in CyHV-2-infected crucian carp.
- Viral proteins with high abundance and early expression, such as ORF88, ORF121, and ORF141, are more likely to generate antigenic peptides.
- Cagi-DDA/DFA MHC-II molecules are highly expressed in spleen and head kidney tissues.

## Abstract

Class II major histocompatibility complexes (MHC-II) are a highly polymorphic and multigenic family of molecules that present exogenous peptides to CD4+ helper T cells, thereby activating the host adaptive immune system. In this study, we systematically analyzed the genomic distribution and tissue-specific expression of MHC-II genes in Carassius gibelio. The Cagi-DDA/DFA molecule was found to be highly expressed in the spleen and head kidney, moderately expressed in the intestine, gills, and trunk kidney, and expressed at low levels in the liver and brain. A polyclonal antibody was generated against the most prevalent Cagi-DDA/DFA allele in the population. Using immunopeptidomics, we identified viral peptides bound to Cagi-DDA/DFA molecules in the head kidney tissues of C. gibelio following Cyprinid herpesvirus 2 (CyHV-2) infection. A total of 276 antigen peptides were identified, originating from 39 viral proteins. Notably, viral proteins with high abundance and early expression profiles, such as ORF88, ORF121, and ORF141 proteins, were more likely to generate antigen peptides. The identified CyHV-2 peptide epitopes presented by C. gibelio MHC-II molecules provide candidate antigens required for anti-CyHV-2 vaccine development.

Vaccination represents a cornerstone in the prevention of infectious diseases, achieving substantial success in disease control. Upon immunization, protein-derived peptides are processed and presented by major histocompatibility complex class II (MHC-II) molecules, activating CD4+ T cells and triggering adaptive immune responses. Cyprinid herpesvirus 2 (CyHV-2), a pathogenic virus in crucian carp, poses a serious threat to global aquaculture. However, the absence of a comprehensive antigenic profile for CyHV-2 has hindered the development of effective vaccines. Here, we employed immunoaffinity purification coupled with mass spectrometry to systematically identify CyHV-2-derived peptides presented by MHC-II in Carassius gibelio. We identified 276 antigenic peptides originating from 39 viral proteins, which collectively delineate the antigenic landscape of CyHV-2 and provide a rational basis for the design of a vaccine against CyHV-2.