The Toll-like receptor (TLR) family in mammalian comprises a family of transmembrane proteins characterized by multiple copies of leucine rich repeats in the extracellular domain and IL-1 receptor motif in the cytoplasmic domain. Up-to-date，ten TLRs (TLR1-10) have been described. TLR2 is differentially expressed in human cells. CD14+ monocytes expressed the highest level of TLR2 followed by CD15+ granulocytes，and CD19+ B-cells. CD3+ T-cells and CD56+ NK cells did not express TLR2. The expression of TLR2 on different cell types are regulated by different immune response modifiers. For example，LPS，GM-CSF，IL-1，and IL-10 up regulate TLR2，whereas IL-4，IFN-gamma，and TNF down regulate TLR2 expression in monocytes.
