Avian CD25+ gamma/delta (γδ) T cells after Salmonella exposure

Although an expansion of distinct γδ T-lymphocyte subpopulations has been shown after Salmonella infection of chicks, functions and activation states of these cells are still largely unknown. To characterize the activation status of avian γδ T lymphocytes after Salmonella exposure, an avian whole-blood Salmonella Enteritidis live-vaccine-strain (SE-LV) stimulation assay and flow cytometry were used, and the bacteria-provoked CD25 antigen expression of CD8-characterized γδ T-cell subsets determined in comparison to αβ T cells. In non-stimulated controls, low numbers of CD25-positive cells were observed in all T-cell populations. The SE-LV stimulation resulted in a significantly enhanced percentage of CD25-expressing CD8α-, CD8αlo+ and CD8ααhi+ γδ T cells accompanied by an increased intensity of the CD25 expression of these cells. Highest values were always seen within the CD8ααhi+ γδ T-lymphocyte subset. The αβ T cells showed no changed CD25 expression. In conclusion, the increased CD25 expression on discrete peripheral T-lymphocyte populations after ex-vivo stimulation demonstrates a Salmonella-induced activation of γδ T-cell subsets and underlines the unique, probably activated character, especially of the avian CD8ααhi+ γδ T cells.