Characterizing the immune response of chickens to Campylobacter jejuni (Strain A74C).

Campylobacter is one of the major foodborne pathogens causing bacterial gastroenteritis worldwide. The immune response of broiler chickens to C. jejuni is under-researched. This study aimed to characterize the immune response of chickens to Campylobacter jejuni colonization. Birds were challenged orally with 0.5 mL of 2.4 x 108 CFU/mL of Campylobacter jejuni or with 0.5 mL of 0.85% saline. Campylobacter jejuni persisted in the ceca of challenged birds with cecal colonization reaching 4.9 log10 CFU/g on 21 dpi. Campylobacter was disseminated to the spleen and liver on 7 dpi and was cleared on 21 dpi from both internal organs. Challenged birds had a significant increase in anti-Campylobacter serum IgY (14&21 dpi) and bile IgA (14 dpi). At 3 dpi, there was a significant suppression in T-lymphocytes derived from the cecal tonsils of birds in the challenge treatment when compared to the control treatment after 72 h of ex vivo stimulation with Con A or C. jejuni. The T-cell suppression on 3 dpi was accompanied by a significant decrease in LITAF, K60, CLAU-2, IL-1β, iNOS, and IL-6 mRNA levels in the ceca and an increase in nitric oxide production from adherent splenocytes of challenged birds. In addition, on 3 dpi, there was a significant increase in CD4+ and CD8+ T lymphocytes in the challenge treatment. On 14 dpi, both pro and anti-inflammatory cytokines were upregulated in the spleen, and a significant increase in CD8+ T lymphocytes in Campylobacter-challenged birds' ceca was observed. The persistence of C. jejuni in the ceca of challenged birds on 21 dpi was accompanied by an increase in IL-10 and LITAF mRNA levels, an increase in MNC proliferation when stimulated ex-vivo with the diluted C. jejuni, an increase in serum specific IgY antibodies, an increase in both CD4+ and CD8+ cells, and a decrease in CD4+:CD8+ cell ratio. The balanced Th1 and Th2 immune responses against C. jejuni might explain the ceca's bacterial colonization and the absence of pathology in Campylobacter-challenged birds. Future studies on T lymphocyte subpopulations should elucidate a pivotal role in the persistence of Campylobacter in the ceca.