T-cell numbers and antigen-specific T-cell function follow different circadian rhythms.

Area of Science:

• Immunology
• Chronobiology

Background:

• Circadian rhythms significantly influence cellular immune responses.
• Understanding daily variations in immune cell function is crucial for human health.

Purpose of the Study:

• To characterize circadian variations in lymphocyte numbers and antigen-specific T-cell functionality in healthy individuals.
• To investigate the daily patterns of T-cell responses to specific antigens under physiological conditions.

Main Methods:

• Quantified blood leukocyte populations over a 24-hour period in six healthy volunteers.
• Analyzed antigen-specific T-cell functionality ex vivo using flow cytometry and intracellular cytokine induction.
• Stimulated whole blood with adenovirus antigen and Staphylococcus aureus enterotoxin B (SEB).

Main Results:

• T-cell numbers and reactivity remained stable during daytime but increased significantly in the late evening and early morning.
• A 1.76-fold increase in T cells reacting to adenovirus antigen and a 1.42-fold increase to SEB were observed (p < 0.0002).
• Peak T-cell reactivity occurred in the late evening, inversely correlating with cortisol levels and not directly coinciding with peak T-cell numbers.

Conclusions:

• Circadian rhythms physiologically regulate T-cell immune responses in human peripheral blood.
• Findings have implications for optimizing blood sampling times for T-cell assays.
• Knowledge of circadian T-cell fluctuations may inform the timing of immunosuppressive drug administration, particularly after organ transplantation.