For example, TLR4 was found to be a receptor for lipolysaccharide (LPS) and essential to generate responses to Gram-negative bacteria in which LPS is a part of the outer membrane (Poltorak et al, 1998), TLR9 responds to DNA-containing unmethylated CpG motifs (Hemmi et al, 2000), TLR3 is activated by double-stranded RNA (Alexopoulou et al, 2001), and bacteria flagellin activates TLR5 (Hayashi et al