Characterization of avian γδ T-cell subsets after Salmonella enterica serovar Typhimurium infection of chicks.

Avian γδ T lymphocytes are frequently found in blood and organs and are assumed to be crucial to the immune defense against Salmonella infections of chicks. To elucidate the so-far-unknown immunological features of subpopulations of avian γδ T cells in the course of infection, day-old chicks were infected orally with Salmonella enterica serovar Typhimurium. Until 11 days after infection, the occurrence as well as transcription of the CD8 antigen and immunologically relevant protein genes of CD8α(-) and CD8α(+high) (CD8αα(+) CD8αβ(+)) γδ cells were analyzed using flow cytometry and quantitative real-time reverse transcription-PCR (RT-PCR) with blood, spleen, thymus, and cecum samples. After infection, an increased percentage of CD8α(+high) γδ T lymphocytes was found in blood, in spleen, and, with the highest values and most rapidly, in cecum. Within the CD8α(+high) subset, a significant rise in the number of CD8αα(+) cells was accompanied by enhanced CD8α antigen expression and reduced gene transcription of the CD8β chain. CD8αα(+) and CD8αβ(+) cells showed elevated transcription for Fas, Fas ligand (FasL), interleukin-2 receptor α (IL-2Rα), and gamma interferon (IFN-γ). While the highest fold changes in mRNA levels were observed in CD8αβ(+) cells, the mRNA expression rates of CD8αβ(+) cells never significantly exceeded those of the CD8αα(+) cells. In conclusion, both CD8α(+high) γδ T-cell subpopulations (CD8αα(+) and CD8αβ(+)) might be a potential source of IFN-γ in Salmonella-infected chicks. However, due to their prominent frequency in blood and organs after infection, the avian CD8αα(+) γδ T-cell subset seems to be unique and of importance in the course of Salmonella Typhimurium infection of very young chicks.