Toll-like receptors (TLRs) recognize specific molecular patterns present only in micro-organisms and thereby activate innate immune cells. TLR2 is essential for the recognition of peptidoglycan and lipoprotein/lipopeptides. Lipoprotein/lipopeptides are observed in cell walls of a variety of micro-organisms. Host immune cells recognize the specific patterns of lipoprotein/lipopeptides through the association of TLR2 with other TLRs. TLR1 and TLR6 are highly homologous to TLR2 in structure. TLR6-deficient mice showed an impaired response to mycoplasmal lipopeptides that are diacylated, whereas TLR1-deficient mice were defective in their response to bacterial lipopeptides that are triacylated. TLR2-deficient mice did not show any inflammatory response to either type of lipopeptide. The functional association of TLR2 with TLR1 or TLR6 has been demonstrated. Thus, TLR1 and TLR6 are involved in the discrimination of a subtle difference between triacyl and diacyl lipopeptides through interaction with TLR2.