Dim Light at Night Increases Immune Function in Nile Grass Rats, a Diurnal Rodent

Jan 6, 2012Chronobiology international

Dim light at night boosts immune response in daytime-active Nile grass rats

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Abstract

Rats exposed to dim light at night showed increased antibody production and enhanced immune function.

Nighttime light exposure is linked to changes in immune function in diurnal species.
Rats in dim light at night exhibited increased swelling in delayed-type hypersensitivity tests, suggesting enhanced cell-mediated immunity.
Increased antibody production was observed following inoculation with keyhole lymphocyte hemocyanin (KLH) in rats exposed to dim light.
Plasma bactericidal capacity was also elevated in rats subjected to nighttime dim light.
Elevated daytime corticosterone levels in these rats may have influenced their immune responses.

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With the widespread adoption of electrical lighting during the 20th century, human and nonhuman animals became exposed to high levels of light at night for the first time in evolutionary history. This divergence from the natural environment may have significant implications for certain ecological niches because of the important influence light exerts on the circadian system. For example, circadian disruption and nighttime light exposure are linked to changes in immune function. The majority of studies investigating the effects of light exposure and circadian disruption on the immune system use nocturnal rodents. In diurnal species, many hormones and immune parameters vary with secretion patterns 180° out of phase to those of nocturnal rodents. Thus, the authors investigated the effects of nighttime light exposure on immunocompetence in diurnal Nile grass rats (Arvicanthis niloticus). Rats were housed in either standard 14-h light (L):10-h dark (D) cycles with L ∼150 lux and D 0 lux or dim light at night (dLAN) cycles of LD 14:10 with L ∼150 lux and D 5 lux for 3 wks, then tested for plasma bactericidal capacity, as well as humoral and cell-mediated immune responses. Rats exposed to dLAN showed increased delayed-type hypersensitivity pinna swelling, which is consistent with enhanced cell-mediated immune function. dLAN rats similarly showed increased antibody production following inoculation with keyhole lymphocyte hemocyanin (KLH) and increased bactericidal capacity. Daytime corticosterone concentrations were elevated in grass rats exposed to nighttime dim light, which may have influenced immunological measures. Overall, these results indicate nighttime light affects immune parameters in a diurnal rodent.

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Dim Light at Night Increases Immune Function in Nile Grass Rats, a Diurnal Rodent

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