All birds used tested negative for Salmonella infection. Animal experimentation was approved

by the Brazilian Committee of Animal Welfare and Ethics (permit number 6236-09). Birds were reared in controlled ambient conditions. A bacterin in oil emulsion containing SE phagotype (PT) 4, PT8 and PT13a antigens, was administered subcutaneously in the nape (0.3 mL/bird) as the killed vaccine (KV). An attenuated mutant SG strain, with deletion on genes cobS and cbiA, unable to synthesize ciano-cobalamin and immunogenic against SE, was used as the live vaccine strain (LV) [10]. An invasive SE PT4 strain [31] was used to challenge birds. Bacterial cultures were prepared MS-275 in Luria-Bertani (LB) broth (Invitrogen, USA) at 100 rpm at 37 °C/24 h. The LV and SE challenge inocula consisted of 108 CFU in Phosphate Buffer Saline (PBS) pH 7.4 (Merck, Germany), administered orally, into the crop. Five groups containing 20 birds each were allocated and vaccination was carried out at 5 and/or 25 days of age, as described in Table 1. At 45 days of age, all birds were challenged. Unvaccinated and unchallenged birds were used as a negative control for DNA Damage inhibitor cytokine quantification. At 1 day before infection (dbi) and 1, 6 and 9 days post-infection (dpi), blood was harvested from five birds in each group,

which were then euthanized by cervical dislocation for sampling. After necropsy, the intestinal lumen was washed with 2 mL phenylmethyl sulfonyl fluoride (PMSF) buffer [33] and centrifuged at 2000 rpm, at 4 °C for 30 min, supernatants were then stored at −20 °C. Spleen, liver and caecal

tonsil samples were aseptically harvested, snap-frozen in liquid nitrogen and stored at −80 °C for immunohistochemistry or quantitative PCR. Spleen and caecal contents were used in bacteriology as described previously [34]. SE counts were expressed as log10 per gram of sample. Positive samples after enrichment (≤102 CFU/g), are expressed as 2 (log10 of CFU/g) in calculations. Indirect enzyme-linked immunosorbent assay (ELISA) using SE antigen was applied to quantify IgG (also known as IgY) and IgM in the sera, and secretory IgA in the intestinal lumen (lavage), Phosphatidylinositol diacylglycerol-lyase as described before [35]. The optical density values (OD) were used to calculate the adjusted E values using the following formula: E value=OD sample−OD negative controlOD positive control−OD negative control Immunohistochemistry was used to determine the influx of CD8+ T cells as described previously [36]. Briefly, frozen tissue sections (8 μm) of liver and caecal tonsil samples were fixed in ice-cold acetone. Sections were incubated overnight at 4 °C with anti-chicken CD8α+ antibody (5 ng/mL, SouthernBiotech, USA). Reaction was developed with Envision-HRP Kit and 3,3′-diaminobenzidine (DAB, Dako, USA). Tissue sections were randomly photographed in light microscope (Eclipse Moticam, Nikon, Japan). The percentage of positively stained areas was analyzed using Image Pro Plus Software (MediaCybernetics, USA).