Circulating γδ T Cells in Response toSalmonellaentericaSerovar Enteritidis Exposure in Chickens

Abstract

γδT cells are considered crucial to the outcome of various infectious diseases. The present study was undertaken to characterizeγδ (T-cell receptor 1⁺[TCR1⁺]) T cells phenotypically and functionally in avian immune response. Day-old chicks were orally immunized withSalmonella entericaserovar Enteritidis live vaccine orS. entericaserovar Enteritidis wild-type strain and infected using theS. entericaserovar Enteritidis wild-type strain on day 44 of life. Between days 3 and 71, peripheral blood was examined flow cytometrically for the occurrence of γδ T-cell subpopulations differentiated by the expression of T-cell antigens. Three different TCR1⁺cell populations were found to display considerable variation regarding CD8α antigen expression: (i) CD8α^+highTCR1⁺cells, (ii) CD8α^+dimTCR1⁺cells, and (iii) CD8α⁻TCR1⁺cells. While most of the CD8α^+highTCR1⁺cells expressed the CD8αβ heterodimeric antigen, the majority of the CD8α^+dimTCR1⁺cells were found to express the CD8αα homodimeric form. After immunization, a significant increase of CD8αα^+highγδ T cells was observed within the CD8α^+highTCR1⁺cell population. Quantitative reverse transcription-PCR revealed reduced interleukin-7 receptor α (IL-7Rα) and Bcl-x expression and elevated IL-2Rα mRNA expression of the CD8αα^+highγδ T cells. Immunohistochemical analysis demonstrated a significant increase of CD8α⁺and TCR1⁺cells in the cecum and spleen and a decreased percentage of CD8β⁺T cells in the spleen afterSalmonellaimmunization. After infection of immunized animals, immune reactions were restricted to intestinal tissue. The study showed thatSalmonellaimmunization of very young chicks is accompanied by an increase of CD8αα^+highγδ T cells in peripheral blood, which are probably activated, and thus represent an important factor for the development of a protective immune response toSalmonellaorganisms in chickens.