This may be because the non-vaccinated group had 0.62 Log 10 CFU/g more Salmonella load at 1wk post-challenge and hence can be expected to be in the process of eliminating the pathogen while the CNP vaccinated group had already cleared the infection by 0.85 Log 10 CFU/g at 2wk post-challenge, which is consistent with the CD4+/CD8+ cells percentage results obtained in this study. This evidence concerns the gene CD4 and infection.