Immunoprofiling of peripheral blood from infectious bronchitis virus vaccinated MHC-B chicken lines – Monocyte MHC-II expression as a potential correlate of protection.

Abstract Vaccination programs are implemented in poultry farms to limit outbreaks and spread of infectious bronchitis virus (IBV), which is a substantial economic burden in the poultry industry. Immune correlates, used to predict vaccine efficacy, have proved difficult to find for IBV-vaccine-induced protection. To find correlates of IBV-vaccine-induced protection, hence, we employed a flow cytometric assay to quantify peripheral leucocyte subsets and expression of cell surface markers of six different non-vaccinated and vaccinated Major Histocompatibility Complex (MHC) haplotypes. Non-vaccinated and vaccinated MHC haplotypes presented differential leucocyte composition and IBV viral load. A strong effect of MHC-B , but not vaccination, on several leucocyte subsets resulted in positive correlations with IBV viral load based on MHC haplotype ranking. In addition, a strong effect of MHC-B and vaccination on monocyte MHC-II expression showed that animals with highest monocyte MHC-II expression had weakest vaccine-induced protection. In conclusion, we found several interesting MHC-B related immune correlates of protection and that flow cytometric analysis can be employed to study correlates of IBV-vaccine-induced protection. Highlights • Strong effect of MHC-B lines, but not vaccination, on peripheral leucocyte composition. • MHC haplotypes present differential IBV viral load and peripheral leucocyte composition. • MHC haplotype ranking in peripheral leucocyte count correlate positively with high IBV viral load. • Animals with high monocyte MHC-II expression have weak vaccine-induced protection. • Flow cytometry can be employed on chicken whole-blood to study IBV vaccine immune correlates. [ABSTRACT FROM AUTHOR]