If a significant time effect was found we described this as a diurnal rhythm. The nTreg-mediated suppression of cytokine synthesis was analyzed using a paired t-test comparing cytokine concentrations in culture supernatants with versus without nTreg. To assess temporal relationships between serum/plasma levels of hormones and cytokine secretion by CD4+ CD25− T cells and their suppression by nTreg, a backward multiple linear regression analysis was calculated. For these analyses individual data were normalized by Z-transformation. Before we analyzed the diurnal Tres and

nTreg activities we compared whether T cells, isolated and sorted using MACS, would give the same results. We observed that MACS-isolated nTreg (Fig. 1), as well as MACS-sorted

nTreg (Fig. S1), significantly suppressed IL-2, IFN-γ and TNF-α secretion by polyclonally stimulated CD4+ CD25− Tres. By MG-132 concentration contrast, the secretion of IL-4, IL-6, IL-10 and IL-17 was not suppressed. For IL-10 and IL-17A, we detected an increase in supernatant levels only if sorted nTreg were added (Figs 1  and S1). Because the assays with MACS-isolated and MACS-sorted T cells produced strikingly similar results, we chose the MACS isolation protocol (which for logistical reasons was more appropriate for the diurnal approach) for diurnal Tres and nTreg activity analyses. NVP-AUY922 molecular weight We also investigated whether αCD3-activated nTreg secrete cytokines and discovered substantial amounts of IL-6, IL-10 and IL-17A, but almost no IL-2, IL-4,

IFN-γ or TNF-α, in the culture supernatants (Figs 1 and S1). Negative controls included adherent cells that were stimulated with αCD3-mAb. None of the analyzed cytokines were detected in these Methane monooxygenase controls (data not shown). These data show that nTreg are suppressors of IL-2, IFN-γ and TNF-α secretion, but not of IL-4, IL-6, IL-10, or IL-17A secretion. Furthermore, our results suggest that nTreg are selective producers of IL-6, IL-10 and IL-17A. To rule out the possibility that cultured nTreg were contaminated with other T cells we cultured CFSE-stained nTreg in co-culture with unstained Tres and measured nTreg proliferation after 62 hr of stimulation with αCD3-mAb in the presence of adherent cells. We did not, however, observe any proliferation of nTreg (Fig. S2). To confirm the nTreg-mediated suppression of cytokine secretion by Tres (shown above), we investigated the reduced proliferation of cytokine-producing Tres through the addition of nTreg, at a single-cell level, using flow cytometry. After culturing Tres in the presence or absence of nTreg, we restimulated the cultures and then co-stained them with αCD4-mAb and αIL-2-, αIL-4-, αIL-10-, αIL-17A, αIFN-γ-, or αTNF-α-mAb. We then quantified the percentage of proliferating, cytokine-producing Tres (Fig. 2a).