Especially important for bacterial infections are TLR2, TLR4 and TLR9: TLR2 is activated by bacterial lipopeptides, TLR4 recognizes endotoxin (LPS) and pneumolysin (an important pathogenic factor of S. pneumoniae), and TLR9 is activated by bacterial DNA [21, 26, 13]. This evidence concerns the gene TLR4 and bacterial infectious disease.