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Dendritic cells are white blood cells that play critical roles in launching the body’s immune response. Typically found in peripheral tissues such as the skin, dendritic cells migrate to the lymph nodes, where they interact with T cells to induce immune responses against pathogens, vaccines, and cancer cells. Findings from a new study suggest that dendritic cell migration is subject to circadian rhythm.

Circadian rhythms are the body’s 24-hour cycles of biological, hormonal, and behavioral patterns. They modulate a wide array of physiological processes, including the body’s production of hormones that regulate sleep, hunger, metabolism, and others. Ultimately, circadian rhythms influence body weight, performance, and disease susceptibility.

The authors of the study collected skin samples from normal (wild type) mice, mice that lack circadian rhythm, and humans at four distinct times during the day and night, corresponding to morning, day, evening, and night. Mice circadian rhythms are similar to humans', but since mice are nocturnal, the rhythms are “flipped.” The authors quantified the number of dendritic cells in the skin samples using immunofluorescence imaging.

They found that the migration patterns of dendritic cells followed a circadian pattern, peaking during the rest phase, which occurred early afternoon for mice and early morning for humans. The drivers of this migration were CCL21 (an antimicrobial cell signaling protein) and adhesion molecules (components of an active T-cell mediated immune response), both of which vary in expression along a gradient throughout the day.

These findings suggest that dendritic cell migration into lymph vessels is subject to circadian rhythm. They also underscore the importance of considering the time of day at which vaccines or immunotherapy treatments are administered.

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