TLR2 is expressed on activated T cells as a costimulatory receptor

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Abstract
Toll is the founder of a group of pattern recognition receptors that play a critical role in the innate immunity in Drosophila. At least 10 distinct Toll-like receptors (TLRs), recognizing pathogen-associated molecular patterns, have now been identified in humans. Most investigations on TLRs have focused on cells of the innate system. We report here that naïve human T cells expressed high levels of cell-surface TLR2 after activation by anti-T cell receptor antibody and IFN-α. Activated cells produced elevated levels of cytokines in response to the TLR2 ligand, bacterial lipopeptide. Furthermore, CD4+CD45RO+ memory T cells from peripheral blood constitutively expressed TLR2 and produced IFN-γ in response to bacterial lipopeptide, which also markedly enhanced the proliferation and IFN-γ production by CD45RO+ T cells in the presence of IL-2 or IL-15. Thus, TLR2 serves as a costimulatory receptor for antigen-specific T cell development and participates in the maintenance of T cell memory. This suggests that pathogens, via their pathogen-associated molecular patterns, may contribute directly to the perpetuation and activation of long-term T cell memory in both antigen-dependent and independent manner.