Seasonality of inflammation in the chicken: clock vs. melatonin control over the pro-inflammatory cytokine gene transcription

Seasonality of immunity in birds has been confirmed, but underlying mechanisms are still not fully explained. Present study was undertaken to verify hypothesis on the role of melatonin in the season-related development of inflammation in chickens. Chickens hatched in summer and winter were kept for 12 days in the season-corresponding LD conditions 16:8 or 8:16, respectively, in continuous illumination (LL) and in LL with melatonin supplementation during subjective night. Peritonitis evoked at two time points (subjective “day” or “night”) by thioglycollate injection stimulated serum lysozyme concentration regardless of lighting conditions and melatonin availability. Pro-inflammatory cytokine IL-6 and IL-18 gene transcription in the spleen exhibited day–night differences, was augmented in inflamed birds in a season-related way, and partially modified by melatonin. Transcription of the core clock genes in the pineal gland was affected by peritonitis confirming a cross-talk between the inflammatory mediators ...