Chronic exposure to dim light at night suppresses immune responses in Siberian hamsters

Abstract

Species have been adapted to specific niches optimizing survival and reproduction; however, urbanization by humans has dramatically altered natural habitats. Artificial light at night (LAN), termed 'light pollution', is an often overlooked, yet increasing disruptor of habitats, which perturbs physiological processes that rely on precise light information. For example, LAN alters the timing of reproduction and activity in some species, which decreases the odds of successful breeding and increases the threat of predation for these individuals, leading to reduced fitness. LAN also suppresses immune function, an important proxy for survival. To investigate the impact of LAN in a species naive to light pollution in its native habitat, immune function was examined in Siberian hamsters derived from wild-caught stock. After four weeks exposure to dim LAN, immune responses to three different challenges were assessed: (i) delayed-type hypersensitivity (DTH), (ii) lipopolysaccharide-induced fever, and (iii) bactericide activity of blood. LAN suppressed DTH response and reduced bactericide activity of blood after lipopolysaccharide treatment, in addition to altering daily patterns of locomotor activity, suggesting that human encroachment on habitats via night-time lighting may inadvertently compromise immune function and ultimately fitness.

Figure 1.

Immune responses to two different challenges. (a) LdimL-hamsters had a suppressed DTH response to challenge with DNFB. (b) Blood plasma bactericidal activity was equivalent at baseline; however, it was enhanced in both groups after LPS-treatment, but to a lesser extent in LdimL-hamsters. Mean ± s.e.m; n = 8–9 per group; *p < 0.05; ⁺p = 0.09. (a) Triangles with solid line, LD; squares with solid line, LdimL. (b) White bars, LD; black bars, LdimL.

Figure 2.

Response to LPS-administration. (a) Both groups mounted an equivalent fever response to LPS. Total home-cage locomotor activity was reduced in LdimL-hamsters during both light and dark phases and LD-hamsters reduced activity to LdimL-hamster levels after LPS-treatment. Mean ± s.e.m; n = 8–9 per group; *p < 0.05. (a) Triangles, LD; squares, LdimL. (b) Open bars, LD saline; filled bars, LdimL saline; open bars with hatched lines, LD post-LPS; filled bars with hatched lines, LdimL post-LPS.