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New research led by Gregory Pearson, a doctoral student in the Department of Psychological and Brain Sciences in the College of Natural Sciences, reveals that the brain’s immune defenses operate on a daily schedule, a finding with potential implications for how we think about respiratory infections and their neurological consequences.

The study, co-authored with Pearson’s colleagues in the Karatsoreos Lab, led by Ilia Karatsoreos, professor of psychological and brain science, and published in Cell Reports, shows that the mouse olfactory bulb, a brain region directly connected to the nasal cavity and a known entry point for viruses like influenza and herpes simplex, rhythmically ramps up antiviral gene expression around dusk, and mounts markedly different immune responses to a nasal viral mimic depending on time of day.

The team also found distinct subpopulations of microglia, the brain’s resident immune cells, whose responses varied with the timing of the challenge. 

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The findings suggest that when a person is exposed to a respiratory pathogen may matter as much as the pathogen itself and could help explain why shift workers and others with disrupted circadian rhythms face elevated risks of infection and inflammatory disease.

The paper, “Time of day alters olfactory bulb immune state with ramifications for intranasal inflammatory challenge,” is online now from Cell Reports.