Differential but Direct Abolishment of Human Regulatory T Cell Suppressive Capacity by Various TLR2 Ligands

Abstract

CD4+CD25high regulatory T cells (Tregs) control cellular immune responses and maintain peripheral tolerance. We investigated whether TLR2 ligands are able to abrogate Treg-induced suppression in humans based on different reports about effects of triacylated lipopeptide Pam3CSK4 in mice. Pretreatment of human Tregs with a mixture of TLR2 ligands Pam2CSK4, FSL-1, and Pam3CSK4 reduced the Treg-mediated suppression of CD4+CD25− responder T cells in the majority of the analyzed donors. Differential effects of individual TLR2 ligands are explained by usage of different TLR2 heterodimers in the recognition of Pam2CSK4, FSL-1, and Pam3CSK4. In contrast to the murine system, TLR2 ligand-mediated abrogation of human Treg function was not associated with a downregulation of FoxP3 transcription factor. Furthermore, our results excluded an effect of TLR2 ligands on granzyme A/B release by human Tregs as a potential mechanism to abolish Treg-mediated suppression. Our data suggest that a downregulation of p27Kip1 and restoration of Akt phosphorylation in human Tregs pretreated with TLR2 ligands result in a reversal of suppression on responder T cells. Moreover, our data indicate that a mixture of TLR2 ligands can be used to modulate human Treg activity.

TLR2 Stimulation Drives Human Naive and Effector Regulatory T Cells into a Th17-Like Phenotype with Reduced Suppressive Function

“…Recent evidence suggests that TLRs are involved in controlling Treg functions (3,4). Previous reports in murine and human cells demonstrated that TLR2 ligation leads to reduced suppressive function of Tregs (4, 10, 11), even when combinations of various TLR2 agonists are used (10). We examined the effect of Pam3Cys and FSL-1 separately on the suppressive functions of magnetic bead-isolated and FACS-sorted Tregs.…”

“…ZaninZhorov et al (12) showed that HSP60 increased Treg suppressive function, and its effects led to activation of signaling molecules PKC, PI3K, and p38. By contrast, recently Oberg et al (10) showed that a mixture of synthetic lipopeptides including Pam3-Cys, FSL-1, and Pam2Cys enhances AKT phosphorylation and reduces Treg function. In fact, a reduced AKT phosphorylation and decreased activation of S6 and FOXO pathways is required for the suppressive function of Tregs (13).…”

“…In human Tregs, various TLR2 ligands including the 60-kDa heat shock protein (HSP60), Pam3Cys, FSL-1, and Pam2Cys have been reported to differentially affect suppressive function by either augmenting or decreasing it (10,12). ZaninZhorov et al (12) showed that HSP60 increased Treg suppressive function, and its effects led to activation of signaling molecules PKC, PI3K, and p38.…”

“…Previous reports in murine cells demonstrated that TLR2 ligation leads to reduced suppressive function of regulatory T cells (Tregs) (4,10,11). In human Tregs, various TLR2 ligands including the 60-kDa heat shock protein (HSP60), Pam3Cys, FSL-1, and Pam2Cys have been reported to differentially affect suppressive function by either augmenting or decreasing it (10,12).…”

γδ-T cells: an unpolished sword in human anti-infection immunity

“…74 For example, both Vd2 75 and Vd1 76 cd-T cells can be activated by TLR4 and TLR5 ligands and exhibit increased antibacteria responses, whereas the specific expression of TLR3 in Vd2 cd-T cells favors their stimulation through this pathway. 74 Moreover, pan-cd-T cells can be activated 77 through stimulation of the heterodimers TLR1/2 and TLR2/6 with a mixture of TLR2 ligands, while the production of Th1 cytokines and the cytolytic activity of cd-T cells can be enhanced by stimulation with double-stranded RNA 78 and DNA 79 through TLR3 and TLR9, respectively, during viral infections.…”