Figure 4.

Diurnal rhythm of cytokine secretion by CD4⁺ CD25⁻ responder T cells (T_res) with and without CD4⁺ CD25^high natural regulatory T cells (nTreg): CD4⁺ CD25⁻ T_res were isolated at five time-points (20:00, 02:00, 07:00, 15:00 and 20:00 hr), using MACS technology, from the peripheral blood of healthy young men over a 24-hr period. The mean purity of T_res was 96·9 ± 0·7% and the mean purity of CD4⁺ CD25^high nTreg was 78·3 ± 8·2%. Cultures of T_res with (open circles) and without (closed circles) nTreg were stimulated with monoclonal αCD3, supernatants were collected after 62 hr and (a) the concentrations of the cytokines interleukin (IL)-2, IL-4, IL-6, IL-10, IL-17A, interferon-γ (IFN-γ) and tumour necrosis factor-α (TNF-α) were measured. (b) For IL-2, IFN-γ and TNF-α, for which the secretion is significantly suppressed through the addition of nTreg, we calculated the suppression ratio as described above. As no effect of sleep was found, data were collapsed from the sleep and the continuous wakefulness conditions and represent mean values ± standard error of the mean (n = 6 in each condition). *P < 0·05; **P < 0·01; ***P < 0·005.