Circulating γ δ T cells in response to Salmonella enterica serovar enteritidis exposure in chickens

gamma delta T cells are considered crucial to the outcome of various infectious diseases. The present study was undertaken to characterize gamma delta (T-cell receptor 1(+) [TCR1+]) T cells phenotypically and functionally in avian immune response. Day-old chicks were orally immunized with Salmonella enterica serovar Enteritidis live vaccine or S. enterica serovar Enteritidis wild-type strain and infected using the S. enterica serovar Enteritidis wild-type strain on day 44 of life. Between days 3 and 71, peripheral blood was examined flow cytometrically for the occurrence of gamma delta T-cell subpopulations differentiated by the expression of T-cell antigens. Three different TCR1(+) cell populations were found to display considerable variation regarding CD8 alpha antigen expression: (i) CD8 alpha(+high) TCR1(+) cells, (ii) CD8 alpha(+dim) TCR1(+) cells, and (iii) CD8 alpha(-) TCR1(+) cells. While most of the CD8 alpha(+high) TCR1(+) cells expressed the CD8 alpha beta heterodimeric antigen, the majority of the CD8a(+dim)TCR1(+) cells were found to express the CD8 alpha alpha homodimeric form. After immunization, a significant increase of CD8 alpha(+high) gamma delta T cells was observed within the CD8 alpha(+high) TCR1(+) cell population. Quantitative reverse transcription-PCR revealed reduced interleukin-7 receptor alpha (IL-7R alpha) and Bcl-x expression and elevated IL-2R alpha mRNA expression of the CD8 alpha alpha(+high) gamma delta T cells. Immunohistochemical analysis demonstrated a significant increase of CD8 alpha(+) and TCR1(+) cells in the cecum and spleen and a decreased percentage of CD8 beta(+) T cells in the spleen after Salmonella immunization. After infection of immunized animals, immune reactions were restricted to intestinal tissue. The study showed that Salmonella immunization of very young chicks is accompanied by an increase of CD8 alpha alpha(+high) gamma delta T cells in peripheral blood, which are probably activated, and thus represent an important factor for the development of a protective immune response to Salmonella organisms in chickens