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Toll was originally found in Drosophila as a pattern recognition receptor associated with defence against fungal and bacterial infections.1,2 Subsequently, toll was found in mammals and named toll-like receptor (TLR). At least 10 distinct TLRs have now been identified in humans.3–9 TLRs are activated by pathogen associated molecular patterns (PAMPs) with target selectivity. PAMPs are integral structural components of pathogens that are thus thought to be essential for survival of infectious organisms and considered to be conserved among a range of pathogens including viruses, bacteria, and fungi. TLRs act as primary sensors of microbial products and activate signalling pathways that lead to the induction of immune and inflammatory genes.10 They belong to a broader family of proteins, which includes receptors for the proinflammatory cytokines interleukin (IL)-1, IL-18 and the orphan receptor T1/ST2.11 All members of this superfamily signal inflammation in a very similar manner. This is due to the presence of a conserved protein sequence in the cytosolic domain called the Toll/IL-1 receptor domain, which activates common signalling pathways, most notably those leading to the activation of the transcription factor NF-κB and stress activated protein kinases.11 Most investigations of TLRs have focused on cells of the innate immune system. This is because TLRs are closely associated with the innate response. However, although innate immunity may constitute the primary function of TLRs, there is no a priori reason why TLRs may not have a direct role in adaptive immunity. We investigated the expression and functions of TLRs on T cells and found that TLR2 is expressed on the surface of activated and memory T cells. Furthermore, it functions as a costimulator receptor molecule for T cell activation and helps to maintain T cell memory. These data suggest a novel role for TLR2 and may …