Short- and Long-Term Chrono-Immune Consequences of Dim Light at Night Exposure in Male Mice at Different Life Stages.

The current use of artificial light during the natural dark phase has acquired contaminant dimensions, known as "light pollution". It is well known that exposure to dim light at night (dLAN) during the postnatal period severely impairs the immune system and related organs, but few reports have demonstrated the effects of dLAN during the fetal period. This study, therefore, examines whether exposure to dim light at night during two critical developmental windows (i.e., prenatal and postnatal periods) leads to long-lasting dysregulation of circadian, behavioral, and immune organization, as well as spleen immune responses, in early adulthood. To address this question, these outcomes were assessed using two defined sampling time points. To answer this question, we exposed two groups of C57BL/6J male mice to dim night light during the gestational and postnatal periods and compared them with control groups that were exposed to light-dark conditions (12 h each, LD). Parametric and non-parametric activity/rest values were analyzed with circular statistics. Compared to their controls, we found differences in alpha, onset, offset, M10, and L5 start time in dLAN groups. We also assessed the transcript levels of clock genes and inflammatory mediators in spleen tissue and found a dampening of daily variation in mRNA expression in both experimental groups. Finally, we used an ovalbumin (OVA) allergy challenge to test the B-cell response in the spleen and found a significantly higher cell recruitment to the spleen and more anti-OVA IgE. Together, these results clearly show that dLAN, at two ZT sampling points, affects peripheral molecular clocks and responses in the spleen, and that these effects are independent of the life stage at which exposure to dim light at night occurs.