 In humans, they have been identified eleven types of recognizing specific pathogen-associated molecular patterns PAMPs. TLR1 and TLR2 form a heterodimer recognizing bacterial tri-acylated lipopeptides of Gram-positive bacteria. TLR2 and TLR6 form another heterodimer recognizing di-acylated lipopeptides of Gram-positive bacteria. TLR4 is a heterodimer recognizing lipopolysacharedes LPSof Gram-negative bacteria while TLR5 is a receptor recognizing flagellae of Gram-negative bacteria. All these aforementioned types of TLRs are expressed on the outer surface of the cell membrane. TLR3, TLR7 TRL8 and TLR9 is a group of receptors expressed on an internal surface of the phagosomes formed in the cytoplasm after the ingestion of the pathogens.TLR3 recognizes viral dsRNA, TLR7 recognizes imidazol-quinollines, TLR8 recognize ssRNA and TLR9 recognize non-methylated bacterial CpG DNA. In addition to bacterial and viral CpG DNA, TLR9 is presumably involved in pathogenesis of autoimmune disorders. TLR10 and TLR11 are still under investigation, although TLR11 seem to recognize uropathogenic bacteria. 