78 Similarly, other purified TLR agonists and inflammatory cytokines that induce the maturation of dendritic cells and augment expression of cell surface molecules that promote T-cell stimulation (e.g. CD80, CD86 and MHC) have also been reported to override Treg-cell suppression through IL-6-independent pathways.79–81 Even in the absence of APCs, cell-intrinsic stimulation through defined TLRs can also trigger shifts in Treg-cell suppression. For example, purified TLR2 agonists stimulate reductions in suppressive potency for mouse Treg cells, and TLR8 agonists trigger similar reductions in potency for human Treg cells.82–84

On the other hand, microbial ligands can also augment Treg-suppressive potency. Mouse CD25+ Treg cells selectively express TLR4,

and lipopolysaccharide stimulation augments their suppressive potency;85 whereas flagellin stimulation via C646 ic50 TLR5 augments the suppressive potency of human Treg cells.86 Taken together, these in vitro studies illustrate the enormous potential whereby microbes and the response to infection can influence immune activation through shifts in Treg-cell suppression. The cumulative impacts whereby pathogens that express multiple TLR ligands and the ensuing immune response on shifts in Treg-suppressive potency have also been characterized for green fluorescent protein-positive (GFP+) cells recovered from Foxp3GFP reporter mice directly ex vivo following infection.87 For example, at Smoothened antagonist relatively early time-points during persistent Salmonella infection, when the activation of effector T cells is blunted and the pathogen burden is progressively increasing, the suppressive potency for GFP+ Treg cells is augmented.59 Conversely, at later infection time-points when effector T cells are highly activated and progressive reductions in pathogen burden occur, the suppressive potency for Foxp3+ cells is reduced. Together IMP dehydrogenase with the waning impacts of Foxp3+ cell ablation with infection progression, these results illustrate how shifts

in Treg-cell suppression can dictate the tempo of persistent infection.59 Similarly, following acute Listeria infection, reductions in suppressive potency are found for GFP+ Treg cells that immediately precede the expansion of pathogen-specific effector T cells.88 The expansion of circulating Treg cells with increased suppressive potency is associated with increased parasite burdens for patients with severe malaria infection.26 However, no significant changes in suppressive potency were found for Foxp3+ Treg cells isolated directly ex vivo after Plasmodium berghei infection in mice.31 Nevertheless, these findings illustrate how infection-induced shifts in Foxp3+ Treg-cell suppressive potency may play important and increasingly appreciated roles in infection outcomes.