Alteration in lymphocytes responses, cytokine and chemokine profiles in laying hens infected with Salmonella Typhimurium

Salmonella Typhimurium has been reported to contaminate egg production across the world, but the exact nature of the immune mechanisms protective against Salmonella infection in laying hens has not been characterized at the molecular level. The experiment was conducted to determine Salmonella colonization and lymphocytes subpopulation in the ileum and spleen, and the mRNA expression of pro-inflammatory cytokines [interleukin (IL)-1β and IL-6], chemokine IL-8, and T helper (Th)1/Th2 cytokines [Interferon (IFN)-γ, IL-12 and IL-18; IL-4 and IL-10 respectively] in the cecal tonsil and spleen of Salmonella challenged hens. Forty Salmonella-free laying hens were challenged orally with Salmonella Typhimurium or phosphate-buffered saline (PBS; control). The Salmonella challenged or non-challenged hens (n = 10) were sacrificed at 2 and 7 days post-infection (DPI). The lymphocyte subpopulation was determined via flow cytometric analysis in the ileum and spleen. The cecal tonsil and spleen samples were collected for mRNA expression through quantitative-RT-PCR. The Salmonella counts were higher (P < 0.05) in the ileum than that in the spleen at 2 and 7 DPI, and were higher (P < 0.05) at 7 DPI than that at 2 DPI in the spleen. Salmonella challenge increased (P < 0.05) ileal CD4+ and CD8α+ cells ratios at 2 and 7 DPI, whereas it increased (P < 0.05) splenic CD8α+ cells ratio only at 7 DPI. The magnitude of increase in ileal CD8α+ cells ratio was higher (P < 0.05) than that in CD4+ cells ratio. The mRNA expression of IL-1β, IL-6, IL-8, IFN-γ, IL-12 and IL-18 were significantly up-regulated in the cecal tonsil of Salmonella challenged hens, and the magnitude of increases in IL-6, IL-8 and IL-12 were significantly higher at 7 DPI than that at 2 DPI. However, Salmonella challenge increased (P < 0.05) the mRNA expression of IL-1β, IL-10 and IL-18 at 2 and 7 DPI, and IL-8 and IFN-γ mRNA only at 7 DPI in the spleen. These findings demonstrated that there appeared the induction of cellular immune responses, and a Th1-cytokines reaction in the intestine and spleen of laying hens infected with Salmonella Typhimurium.