Daily oscillations are present in many aspects of the immune system, including responsiveness to infections, allowing temporal alignment of defence mechanisms with the external environment. Our study addresses whether compromised circadian timing function by dim artificial light at night (ALAN) impacts the time dependency of the acute inflammatory response in a rat model of lipopolysaccharide (LPS)-induced inflammation. After 2 weeks of exposure to low-intensity ALAN (~2 lx) or a standard light/dark cycle, male rats were challenged with LPS during either the day or the night. Dim ALAN attenuated the anorectic response when rats were stimulated during their early light phase. Next, ALAN suppressed daily variability in inflammatory changes in blood leukocyte numbers and increased the daytime sensitivity of neutrophils to the priming effects of LPS on oxidative burst. An altered renal inflammatory response in ALAN-exposed rats was manifested by stimulated T-cell infiltration into the kidney upon night-time LPS injection and the modified rhythmic response of genes involved in inflammatory pathways. Moreover, ALAN disturbed steady-state oscillations of the renal molecular clock and eliminated the inflammatory responsiveness of Rev-erbα. Altogether, dim ALAN impaired time-of-day-dependent sensitivity of inflammatory processes, pointing out a causal mechanism between light pollution and negative health effects.
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