T Cell Subset Profile And Inflammatory Cytokine Properties In The Gut-associated Lymphoid Tissues Of Chickens During Infectious Bursal Disease Virus (IBDV) Infection

Infectious bursal disease(IBD)is one of the important diseases in poultry farming,which has the characteristics of high pathogenic ity,high infectivity and immunosuppression.The causative agent of IBD is Infectious bursal disease virus(IBDV),belonging to the double-stranded RNA(ds RNA)virus family(Birnaviridae).Gut associated-lymphoid tissues(GALTs)mainly include cecal tonsils(CTs),esophageal tonsils(ETs),pyloric tonsils(PTs),and Meckel's diverticulum,play an important role in defending against external bacteria and viruses.While IBDV infection mainly targets immature B lymphocytes and contributes to enhanced T cell infiltration in the bursa of Fabricius of birds,the impact of IBDV infection on that of immune cells in avian GALTs remains elusive.To this end,this study aims at investigating the effect of IBDV infection on the dynamic changes of different T cell subsets and the expression of related inflammatory cytokines in the gut associated-lymphoid tissues of chickens.The viral proteins were detected in the bursa of Fabricius,cecal tonsils and spleens from SPF chickens infected with IBDV.H&E staining showed that IBDV infection caused submucosal edema and congestion of the caecum tonsil and enlarge the splenic cell space.Flow cytometry analys is showed that in BFs and spleen,IBDV infection did not affect the number of CD8+ T cells,but significantly increased the proportion of CD4~+ T cells.While T cell subsets of esophageal tonsils and Merkel's diverticulum are not affected by IBDV infection,interestingly,in CTs,IBDV infection signif icantly reduced the percentage of CD4~+ T cells.In addition,it was observed that the proportion of CD4~+CD8+ double pos itive T cells in BFs and pyloric tonsils increased signif icantly.q RT-PCR analysis showed that in the bursa of Bursa,the m RNA expression of cytokines IL-10,IFN-? and the T-cell checkpoint receptor LAG-3 gene was signif icantly up-regulated at 5dpi.Similar ly,in the spleen,IBDV infection at 5dpi also up-regulated the m RNA level of IFN-?.In contrast,in CTs,the m RNA expression of IFN-?,IL-10 and receptor LAG-3 was not changed,but the m RNA expression of CTLA-4,another important T cell checkpoint receptor,was significantly decreased.Taken together,we have demonstrated IBDV infection causes the differential changes in T cell subsets,the expression of T cell surface checkpoint receptor genes and the expression of inflammatory cytokines in different avian intestinal related immune tissues.In particular,IBDV suppresses the frequency of CD4~+ but not CD8+ T cell subsets in CTs and the expression of CTLA-4 molecules.Our results have thus broadened the understanding of the interaction of IBDV with the host immune system.