Effect of Salmonella infection on cecal tonsil regulatory T cell properties in chickens

Two studies were conducted to study regulatory T cell [Treg (CD4⁺CD25⁺)] properties during the establishment of a persistent intestinal infection in broiler chickens. Four-day-old broiler chicks were orally gavaged with 5 × 10⁶ CFU/mL Salmonella enteritidis (S. enteritidis) or sterile PBS (control). Samples were collected at 4, 7, 10, and 14 d postinfection. There was a significant (P < 0.05) increase in the number of CD4⁺CD25⁺ cells by d 4 postinfection that increased steadily throughout the course of the 14-d infection, whereas the number of CD4⁺CD25⁺ cells in the noninfected controls remained steady throughout the study. CD4⁺CD25⁺ cells from cecal tonsils of S. enteritidis-infected birds had a higher (P < 0.05) IL-10 mRNA content than CD4⁺CD25⁺ cells from the noninfected controls at all time-points studied. The amount of IL-2 mRNA content in the cecal tonsil CD4⁺CD25⁻ cells from the infected birds did not differ (P > 0.05) when compared to that of noninfected control birds. At a lower effector/responder cell ratio of 0.25:1, CD4⁺CD25⁺ cells from cecal tonsils of Salmonella-infected birds suppressed T cell proliferation at d 7 and 14 post-S. enteritidis infection, while CD4⁺CD25⁺ cells from noninfected control groups did not suppress T cell proliferation. In the second studu, 1-day-old chickens were orally gavaged with PBS (control) or 1.25 × 10⁸ CFU/bird S. enteritidis. At 7 and 21 d post-Salmonella infection, CD25⁺ cells collected from cecal tonsils of S. enteritidis-infected birds and restimulated in vitro with Salmonella antigen had higher (P < 0.05) IL-10 mRNA content compared to those in the control group. Spleen CD4⁺CD25⁺, CD4⁺, and CD8⁺ cell percentage did not differ (P > 0.05) between the Salmonella-infected and control birds. In conclusion, a persistent intestinal S. enteritidis infection increased the Treg percentage, suppressive properties, and IL-10 mRNA amounts in the cecal tonsils of broiler birds.