TLR4 and infection: However, mouse strains that express an impaired TLR4 in their immune cells (C3H-HeJ) are susceptible to lethal and sublethal leptospirosis (Pereira et al., 1998; Nally et al., 2005; Viriyakosol et al., 2006; Richer et al., 2015) and those that have been engineered to not express TLR4 (C57BL/6J-TLR4ko) succumb to infection (Chassin et al., 2009).