Summary of HDAC biology and Tregs, using a schematic adapted from Bush and McKinsey [71]. Note that * class IIa HDACs are currently thought to act primarily through protein/protein interactions and their deacetylase activity is mediated via recruitment of a class I HDAC, such as HDAC3; and **HDACi acting on Zn-dependent HDACs (class I, IIa and IV) are distinct from HDACi that act on NAD-dependent sirtuins (Class III). There are HDAC specific inhibitors for HDAC6 and Sirt1 (20••, 21••). Abbreviations are HDAC, histone/protein deacetylase; HSF, heat shock factor; HSP, heat shock protein; MEF-2, myocyte enhancer factor-2; NAD, nicotinamide adenine dinucleotide; and. Sirt1, Sirtuin-1.