Salmonella is a ubiquitous pathogen which, in addition to causing poultry diseases, has a growing zoonotic impact. It has demanded the implementation of diverse control strategies, in which vaccines play a major role. The understanding of the immune pathways elicited by the different vaccines is important, contributing for the establishment of strong immune correlates of protection, for instance. With the purpose of determining the dynamics of the humoral and cellular immune responses to vaccination, broiler breeders (Cobb Slow) were immunized with live or inactivated vaccines against Salmonella Enteritidis. Lymphocyte and macrophage subsets were analyzed in the peripheral blood by flow cytometry and antigen-specific circulating IgY and mucosal IgA were quantified. The markers analyzed by flow cytometry were CD8/CD28, CD4/TCRVβ1, Kul/ MHC II and Bu-1. Both live and inactivated vaccines induced an increase in the proportion of circulating monocytes (Kul + MHCII + ) in some time points compared to non-vaccinated controls. However, whereas the live vaccine leads to an increase in CD8 − CD28 + and Bu-1 + lymphocytescompared to the control group, the inactivated vaccine prompteda reduction in the percentage of severalleucocyte subsets (Kul − MHCII + , Bu-1 + , CD8 + CD28 + , CD8 − CD28 + , CD4 + TCRVβ1 − , CD4 + TCRVβ1 + , CD4 − TCRVβ1 + ) after the boost dose. Both vaccines induced specific serum IgY and mucosal IgA production; however, the inactivated vaccine stimulated higher titers in a shorter period. These results contribute to the understanding of mechanisms of action of live and inactivated Salmonella vaccines in chickens.

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BackgroundChicken Infectious Anaemia (CIA) Virus (CAV) curtails the function of multiple immune compartments. Mortality due to blatant infection is controlled in broilers by passive immunization derived from vaccinated breeders. Therefore, chicks are often assessed by serology to determine maternally-derived antibodies (MDA).MethodsA vaccine overdose-induced model of CIA. The model replicated the most common features of the disease. This model was used to determine the role of MDA in the protection of chicks. Hatchlings were tested for anti-CAV by ELISA and were sorted into groups based on antibody levels. SPF chicks were used as a no-antibody control.ResultsLower specific antibody levels seemed to facilitate viral entry into the thymus, but viral levels, CD4+and CD8+counts, thymus architecture, and haematocrit were preserved by MDA, regardless of its levels.ConclusionLevels of MDA are not correlated with CIA, but are important for CAV infection.IMPORTANCEVaccination is paramount in broiler production. Many of the vaccines are given to broiler breeders, instead of to the broilers themselves. This is cost-effective and practical, since in vaccinating one breeder hundreds of broilers are born with maternally-derived protection. To assess the quality of maternal immunity, antibodies are measured in their chicks. For Chicken Anaemia, this does not seem to suffice to verify protection. This viral disease is very common, and measuring maternal immunity against it determines whether to purchase chicks from a breeder farm. In this study, we verified that antibodies are not correlated with protection from the disease, and therefore should not be used as the sole parameter in assessing immunity against Chicken Anaemia in broilers.