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

ABSTRACTChicken genetics and age affect resistance to enteric infection withSalmonella entericaserovar 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 61chickens 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 61and line N chickens, except for higher levels of IL-1β in the spleens of line 61chickens 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 entericS. entericaserovar 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 ofS. entericaserovar Typhimurium from the intestine of infected chickens.