05). IFN-γ levels were significantly augmented in vaccinated groups in comparison to unvaccinated birds, in spleen and caecal tonsils ( Fig. 3) before challenge. IFN-γ expression

in caecal tonsils was significantly elevated in groups C and E at 1 dbi, and at 6 dpi in group E, in comparison with the other groups (p < 0.05). IL-10 was highly expressed in spleen samples of all vaccinated groups in comparison with group A at 1 dbi (p < 0.05). At 1 dpi, the expression of this cytokine in spleen decreased in all groups, except in group D. In caecal tonsils, IL-10 levels were higher in groups C and E before challenge, and a peak was seen at 6 dpi in group signaling pathway E ( Fig. 3). The recruitment of CD8+ T cells in liver and caecal

tonsils, evaluated by immunohistochemistry, is displayed in Fig. 4. Before the challenge, at 1 dbi, all groups had low levels of CD8+ T cells in caecal tonsil. HDAC inhibitor review At 1 dpi, the influx of CD8+ T cells started to increase in all groups, including the unvaccinated group A. At 6 dpi, cell influx was significantly higher in groups A and C, and at 9 dpi, groups B and C showed the highest levels of CD8+ T cells (p < 0.05), in caecal tonsil samples however, groups D and E exhibited significantly lower levels of CD8+ T cells, similar to the unvaccinated group A. In liver samples, CD8+ T cells were present at 1 dbi, although, only groups B, C and E were significantly different from the control group A. After challenge, the cell influx in the liver was clearly increased in all groups, and the highest levels were seen in group A; values in group D were constant and had no significant increase during this period. At 6 dpi,

the amount of CD8+ T cells was not different between SDHB vaccinated groups (p > 0.05). However, at 9 dpi, groups B and C showed higher numbers of CD8+ T cells than groups D and E in liver. Studies regarding the influence of live and killed vaccines on the immune responses of commercial chickens are important to clarify the specific mechanisms involved. Discussions about the use of Salmonella vaccines are always controversial; live vaccines are often questioned about reversion to virulence, whilst killed vaccines are described as weak stimulators of the CMI [18] and [38]. The present study, and others, demonstrates that bacterins stimulate the humoral response which is ineffective on its own, to control Salmonella infection [39]. However, KV can reduce Salmonella burden in poultry flocks when used with a biosecurity program [5] and [40]. Immune responses generated by invasive live vaccines should trigger similar processes as the pathogenic strains. The mutant SG invaded the host organism from the gut and colonized internal organs similarly to the wild strain [10]. Additionally vaccine strains with known genetic deletions (GMO) have reduced risks of reversion to virulence, in comparison with rough strains [41].