Cytokine and chemokine expression in the caecal tonsils associates with caecal Campylobacter load in chickens

Levels of Campylobacter colonisation in the ceaca can differ significantly between and within birds. Local immune responses for pathogens found in caeca have been studied as cytokine expression in the caecal tonsils. The objectives of the present study was to investigate the level of local immune response after Campylobacter jejuni (C. jejuni) challenge in relation with the level of C. jejuni colonisation in the caeca and the difference in gene expression between the two tonsils. Two experiments were conducted. The first, involved 30 White Leghorn layers raised under SPF conditions from day to hatch. All birds were experimentally challenged with C. jejuni at 3 weeks of age. The second experiment involved 60 birds from two broiler lines that were naturally infected with Campylobacter in farm conditions. Campylobacter load in the caeca was determined by selective culture and mRNA levels of two cytokines (interleukin-1 (IL-1) and interleukin-6) and two chemokines (CXCLi-1 and CXCLi-2) were quantified by real-time quantitative RT-PCR for all the birds. Pearson’s correlation to compare the gene expression in the two tonsils, mixed model analysis to identify factors affecting gene expression and bivariate analysis of Campylobacter load and gene expression were performed. No significant (P>0.05) correlations were identified between the two tonsils, implying that gene expression results of one tonsil are not representative for the other. Strong high positive correlations between C. Jejuni load and IL-1 and CxCLi2 were estimated at 1 week post-infection in the White Leghorns but not in the broilers. The latter could be attributed to the fact that these birds were maintained in a low biosecurity environment known to provide Eimeria challenge. Finally, a significant effect of sex, breed and caecal tonsil on the cytokine and chemokine expression in the tonsils of the broilers was identified.