Figure 1.

There are 10 members of the TLR family in humans. These are evolutionary-conserved homologs of the Drosophila Toll protein that play a key role in the innate immune response to pathogen-derived and endogenous danger signals (see Chen and DiPietro⁷⁶ for a complete description of TLR ligands). TLR10 is unique among the repertoire of TLRs as it appears to function to suppress inflammatory signaling and currently has no known ligand. TLRs 1, 2, 4, 5, 6, and likely 10 are found on the cell surface whereas TLRs 3, 7, 8, and 9 localize to intracellular compartments (e.g., endosomes and lysosomes). TLR, toll-like receptor.