These studies indicate that a NAC concentration ≥0.1 mM in the extracellular milieu is sufficient to inhibit or block suppression.
Some of these suppressive effects were mediated by IFN-α, as demonstrated by the ability of an anti-IFN-αR antibody to partially block suppression; however, the data also suggested involvement of additional factors.
Interestingly, the addition of TGFβ neutralizing antibodies still had a small but significant effect on blocking suppression (suppression = 2.3% ±1.2 for a 1∶1 ratio of Tregs:Teff with 30 µg/mL anti-TGFβ), essentially eliminating what residual suppression remained (p = 0.02 for the comparison of a 1∶1 ratio with and without anti-TGFβ).
T-reg cells require low levels of some cytokines in order to differentiate from naive CD4+ T cell precursors, with high levels blocking suppression.
Studies in IL-2-deficient mice show that IL-2 is essential for Treg cell generation, and whereas high concentrations of IL-2 can block suppression, low levels of IL-2 modulate their development and maintenance (Scheffold et al., 2005).
Members of the tumour necrosis factor (TNF) receptor superfamily, including GITR, OX40, 4-1BB and RANK are expressed by Treg cells and their ligation can block suppression, increase proliferation, or both (Choi et al., 2004; Kanamaru et al., 2004; Valzasina et al., 2005).
We found that deacylase depletion increased K122 acylation on SOD1, which blocked the suppression of respiration in a K122-dependent manner.
AICAR (0.5 mM) or Rapamycin (25 µg), at doses that do not alter ingestion, completely blocked the suppression of food intake induced by an i.c.v.
The neutralizing anti-IFN-αR antibody blocked HIV suppression to a widely variable and not significantly different degree in all three patient groups (Figure 4A), in agreement with their comparable levels of IFN-α production.
