A strong antigen-specific T-cell response is associated with age and genetically dependent resistance to avian enteric salmonellosis

Abstract

Chicken genetics and age affect resistance to enteric infection with Salmonella enterica 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(1) 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-1beta (IL-1beta) and gamma interferon (IFN-gamma) mRNA were similar in the spleens and cecal tonsils of both line 6(1) and line N chickens, except for higher levels of IL-1beta in the spleens of line 6(1) chickens at 6 days postinfection. Differences in the levels of IFN-gamma and IL-1beta 1beta 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 S. enterica 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 S. enterica serovar Typhimurium from the intestine of infected chickens.

FIG. 1.

Antigen-specific proliferation of splenocytes from line N and line 6₁ chickens infected with S. enterica serovar Typhimurium 40 days after hatching as measured by incorporation of [³H]thymidine. The error bars indicate standard errors (n = 5). Regression analysis using the F test between the infected line N and line 6₁ chickens resulted in a P value of 0.026. dpi, days postinfection.

FIG. 2.

Antigen-specific serum IgM (A), IgG (B), and IgA (C) in line N and 6₁ chickens infected with S. enterica serovar Typhimurium 40 days after hatching. The error bars indicate standard errors (n = 5). a and b indicate that there were significant differences between infected and uninfected line N and 6₁ chickens, respectively (as determined by a t test). An asterisk indicates that there was a significant difference between infected line N and line 6₁ chickens (P < 0.05). dpi, days postinfection.

FIG. 3.

Changes in expression of IFN-γ (A and B) and Il-1β (C and D) mRNA as determined by quantitative RT-PCR in the spleens (A and C) and cecal tonsils (B and D) of chickens infected with S. enterica serovar Typhimurium 40 days after hatching. The data are expressed as fold increases compared to uninfected control chickens. The error bars indicate standard errors (n = 5). An asterisk indicates that there was a significant difference in mRNA expression between infected chickens and uninfected controls (as determined by a t test). dpi, days postinfection.

FIG. 4.

Antigen-specific proliferation of splenocytes from line N and line 6₁ chickens infected with S. enterica serovar Typhimurium 10 days after hatching as measured by incorporation of [³H]thymidine. The error bars indicate standard errors (n = 5). No statistical differences were observed between any groups, as determined by regression analysis. dpi, days postinfection.

FIG. 5.

Antigen-specific serum IgM (A), IgG (B), and IgA (C) in line N and 6₁ chickens infected with S. enterica serovar Typhimurium 10 days after hatching. The error bars indicate standard errors (n = 5). a and b indicate that there were significant differences between infected and uninfected line N and 6₁ chickens, respectively (as determined by a t test). An asterisk indicates that there was a significant difference between infected line N chickens and infected line 6₁ chickens (P < 0.05). dpi, days postinfection.

FIG. 6.

Changes in expression of IFN-γ (A and B) and Il-1β (C and D) mRNA as determined by quantitative RT-PCR in the spleens (A and C) and cecal tonsils (C and D) of chickens infected with S. enterica serovar Typhimurium 10 days after hatching. The data are expressed as fold increases compared to uninfected control chickens. The error bars indicate standard errors (n = 5). An asterisk indicates that there was a significant difference in mRNA expression between infected chickens and uninfected controls (as determined by a t test). dpi, days postinfection.