Dynamics of Lymphocyte Subpopulations in Immune Organs of Chickens Infected with Salmonella enteritidis

To determine the effect of different doses of Salmonella enteritidis on immunocompetent cells, the thymus, bursa of Fabricius, and peripheral blood were examined.One-day-old chickens were orally infected with 2 × 10 2 CFU/ml (low dose) and 2 × 10 8 CFU/ml (high dose) of S. enteritidis PT4.Subsets of T lymphocytes (CD3, CD4, and CD8), and BU1b cells using an indirect immunofluorescent method and flow cytometry were analysed on days 7, 10, 14, 21, and 27 postinoculation (dpi).The actual number of lymphocytes in the peripheral blood showed a significant increase in the low dose group (P < 0.05) on day 21 pi, and in the high dose group on day 27 pi (P < 0.001) compared to controls.The increase of CD3+, CD4+, and CD8+ T cells was observed in both infected groups compared to the controls from day 14 pi, significant on day 21 pi (P < 0.05) in the high dose group.The subpopulation of CD8+ was higher also on day 27 pi (P < 0.01) compared with the values of the control group.The subpopulation of BU1b+ B cells in both infected groups showed higher values, but without significant differences from controls.The thymus T lymphocytes showed a significant decline in CD3+ T cells on day 7 pi, whereas CD4+ T cells were significantly (P < 0.05) increased on day 7 pi in both infected groups.The bursal lymphocytes showed a decrease in BU1b+ B cells in both infected groups compared with the control group, significant in the high dose group on day 21 pi (P < 0.05).These results indicate that S. enteritidis infection induced the changes in immunocompetent cells, included cellular and humoral immune response.Salmonella infection accelerated the maturation and differentiation of thymus T cells in the first phase of infection, what was secondarily reflected by increased number of studied T lymphocyte subpopulations in the peripheral blood from day 14 to 27 after infection.Similarly, it appears that the activation of B cells in bursa of Fabricius caused the decrease number of bursal B lymphocytes and increased number of these cells in the peripheral blood from day 14 to 27 pi in both infected groups. Salmonella enteritidis, immune response, flow cytometry, lymphocyte subpopulations, chickensSalmonella enteritidis (S. enteritidis) has become the most important cause of human food poisoning throughout the world in recent years.Current research has attempted to identify the defence mechanism of chickens against S. enteritidis (Arnold and Holt 1995).Salmonella invades the intestinal epithelium and stimulates mucosal immunity.In chickens the cell-mediated immune response has been shown to play an important role in host protection against many intracellular pathogens (Schat 1994;Kaufmann 1995;Lillehoj and Trout 1996).Sasai et al. (1997) reported that S. enteritidis infection induces changes in the lymphocyte subpopulations in the spleen and thymus that reflect the dynamics of the host's protective immune response.Although some aspects of cellular immune responses to S. enteritidis have been examined in chickens, the exact protective immune mechanism remains to be determined.In the present study, the percentage of CD3, CD4, CD8 T cells, and BU1b B cells in the thymus, bursa of Fabricius and peripheral blood of one-day-old chickens orally infected with S. enteritidis were investigated.