TLR4 is a key sensor for infection-induced preterm birth, since protection is afforded in mice by spontaneous mutation of Tlr4 in C3H/HeJ mice27, 29, 30, null mutation of Tlr4 in C57Bl/6 mice22, 30, and genetic deficiency in the MyD88 and TRIF adaptor proteins required for TLR4 signaling28. This evidence concerns the gene TLR4 and infection.