TLR2 stimulation drives human CD4+CD25+CD127negFOXP3+ Tregs into a Th17-like phenotype with reduced suppressive function. (50.4)

Abstract

Abstract Naturally occurring CD4+CD25hiFOXP3+ Tregs suppress the activity of pathogenic T cells and prevent development of autoimmunity. TLRs are involved in modulating Treg functions both directly and indirectly. Specifically, TLR2 stimulation can reduce the suppressive function of Tregs by mechanisms that are incompletely understood. The developmental pathways of Tregs and Th17 cells are considered divergent and mutually inhibitory, and IL-17 production has been associated with reduced Treg function. We examined the effect of different TLR2 ligands on the suppressive functions of human CD4+CD25hiCD127negFOXP3+ Tregs and found that activation of TLR1/2 heterodimers reduces the suppressive activity of Tregs on CD4+CD25- responder T cell (Tresp) proliferation while at the same time enhancing the expression of IL-17, increasing RORC, and decreasing FOXP3 expression. Neutralisation of either IL-17 or IL-6 abrogated Pam3Cys-mediated reduction of Treg suppressive function. We also found that TLR2 stimulation in combination with TCR activation drives naïve human T helper precursors to Th17 differentiation. We conclude that TLR2 stimulation can induce human Tregs to a Th17 phenotype skewing and identify this plasticity as a new mechanism of regulation of Treg function by TLRs, which could enhance microbial clearance by releasing T effector functions.