TLR4 and infection: Indeed, in a previous study, no severe clinical symptoms were observed in WT mice after infection with L. interrogans serovar Copenhageni strain Fiocruz F1-130, whereas TLR4−/− mice were more susceptible, developing lethal acute leptospirosis upon infection with the same dose.14 In the present study, no lethality was observed in either WT or TLR4−/− mice after infection with strain 56606v.