Rhythmatic immune response to <i>Campylobacter jejuni</i> inoculation revealed by immune factors level in serum

1. This study examined the rhythmatic immune response of chickens in the early stages of <i>Campylabacter jejuni</i> infection over time. Chickens were inoculated with <i>C. jejuni</i> at 10:00, 14:00 and 18:00 h, respectively.2. The <i>C. jejuni</i> populations in the caecal and the levels of IL-8, IL-18, IL-1β, IgA, IgY and cytokine signal transduction inhibitor 3 protein (SOCS3) in serum for each individual were measured at different hours after inoculation (hpi). Cosine and regression analyses were assessed for rhythmicity and correlations.3. The log₁₀CFU of <i>C. jejuni</i> number in the caecal content was the lowest (7.4-8.1) at 10:00 h and highest (9.4-9.8) at 18:00 h. Inoculation status and time points post-inoculation had significant effects on IL-8, IL-18, IL-1β, IgA, IgY and SOCS3 levels (<i>p</i> < 0.001). The IL-8, IL-18, IL-1β and IgY levels at 16 hpi were the lowest compared to other <i>post</i>-inoculated time points.4. The IL-8, IL-1β, IgA and SOCS3 levels of the control and treated groups showed rhythmic changes at 18:00 (<i>p</i> < 0.05). Caecal <i>C. jejuni</i> colonisation was significantly correlated with levels of IL-18, IL-1β, IgA, IgY and SOCS3 (<i>r</i> = 0.35-0.76; <i>p</i> < 0.05), among which IgY had the highest correlation coefficient (<i>r</i> = 0.76; <i>p</i> < 0.0001).5. Chickens were more sensitive to <i>C. jejuni</i> inoculation administered at 18:00 h. Moreover, the changes of IgA, IL-8 and IL-1β levels were lowest at 16 hpi and more likely to show circadian rhythms in chickens inoculated at 18:00 h.