Dynamic alterations in T-lymphocyte subsets assessed by flow cytometry in chickens following exposure to infectious bursal disease virus: A systematic review

Infectious bursal disease virus (IBDV) is a significant pathogen in poultry, causing acute immunosuppressive disease in young chickens. While B-lymphocyte involvement in IBDV pathogenesis is known, the role of T-cells is incompletely understood. This systematic review presents the alterations in chicken T-lymphocyte subsets after IBDV exposure, assessed by flow cytometry analysis. Four databases were queried for identifying eligible studies focused on experimental infections measuring T-lymphocyte changes in the bursa of Fabricius, spleen, thymus, and peripheral blood mononuclear cells. Of 488 studies found, 25 met the pre-established criteria and were included in the qualitative synthesis of results. Most studies analysed T-lymphocyte responses during the acute phase of IBDV infection, primarily focusing on CD4+ and CD8+ T-cells. Other subsets, such as γδ T-cells and double-positive CD4+CD8+ T-cells, were less frequently investigated. An increase in T-lymphocytes was noted in the bursa of Fabricius, suggesting their active role in viral clearance. In the spleen, CD4+ T-cells commonly increased, while CD8+ responses varied among studies. Increased levels in T-cells were also noted during the chronic infection in the bursa of Fabricius, possibly due to persistent viral antigens. Overall, variations in flow cytometry methods and T-cell output reporting were noted among studies. Based on the data collected, further investigation into diverse T-cell subpopulations beyond CD4+ and CD8+ is needed, as well as the standardization of flow cytometry assays in chickens.