A Strong Antigen-Specific T-Cell Response Is Associated with Age and Genetically Dependent Resistance to Avian Enteric Salmonellosis

<jats:title>ABSTRACT</jats:title> <jats:p>Chicken genetics and age affect resistance to enteric infection with <jats:italic>Salmonella enterica</jats:italic> serovar Typhimurium and were used to identify the immune responses that may contribute to rapid clearance. When birds were infected at 40 days of age, line 6<jats:sub>1</jats:sub> chickens cleared the infection more effectively than line N chickens, whereas when birds were infected at 10 days of age, both chicken lines were highly susceptible to infection. Antibody levels, T-cell responsiveness, and cytokine mRNA levels were all elevated during infection. A negative correlation between resistance and antigen-specific antibody production was observed in older chickens. However, this finding was not replicated for age-related resistance; we found that older chickens exhibited a stronger and more rapid antibody response than younger chickens. The levels of interleukin-1β (IL-1β) and gamma interferon (IFN-γ) mRNA were similar in the spleens and cecal tonsils of both line 6<jats:sub>1</jats:sub> and line N chickens, except for higher levels of IL-1β in the spleens of line 6<jats:sub>1</jats:sub> chickens at 6 days postinfection. Differences in the levels of IFN-γ and IL-1β 1β mRNA between the lines were more apparent in younger chickens, but while the increases were greater than those observed in the older chickens, the clearance of enteric <jats:italic>S. enterica</jats:italic> serovar Typhimurium was much slower. The level of antigen-specific proliferation of splenocytes was associated with increased resistance in both experimental systems, and the strongest responses were observed in older and genetically resistant chickens. The data presented here implicate T-cell responses in the clearance of <jats:italic>S. enterica</jats:italic> serovar Typhimurium from the intestine of infected chickens.</jats:p>