Lack of Association between theTlr4(Lpsd/Lpsd) Genotype and Increased Susceptibility to Escherichia coli Bladder Infections in Female C3H/HeJ Mice

Abstract

ABSTRACTToll-like receptor 4 is thought to have a primary role in host defense against Escherichia coli bladder colonization, based on mouse models of urinary tract infection using C3H/HeJ female mice. This strain carries a point mutation in the Tlr4 gene, which renders the mice unresponsive to lipopolysaccharide (LPS) and thus limits the bladder inflammatory response and infection resolution. The importance of Tlr4 as the sole genetic determinant of resistance or susceptibility can be questioned, however, by the observation that C3H/HeOuJ female mice with a functional Tlr4 do not effectively resolve E. coli bladder infections. The present study further examined this inconsistency by investigating the association of Tlr4 Lpsd and Lpsn alleles with bladder infection susceptibility by using genetic crosses of C3H/HeJ mice with Tlr4 (Lpsn/Lpsn) or (Lpsn/Lpsd) mice. Heterozygous offspring of C3H/HeJ (Lpsd/Lpsd) × BALB/cAnN (Lpsn/Lpsn) mice successfully resolved bladder infections induced by a uropathogenic E. coli strain, while heterozygous mice from a C3H/HeJ (Lpsd/Lpsd) × C3H/HeOuJ (Lpsn/Lpsn) cross had severe infections. A backcross of C3H/HeJ (Lpsd/Lpsd) with (BALB/cAnN × C3H/HeJ)F1 (Lpsn/Lpsd) produced mice that were either resistant or susceptible to E. coli bladder infections and had Lpsd/Lpsd or Lpsn/Lpsd Tlr4 genotypes. The Lpsd/Lpsd or Lpsn/Lpsd genotypes were present in individual mice with unresolved bladder infections, and the Lpsd/Lpsd genotype was found in infection-resistant mice. These results indicate that at least one gene other than Tlr4 strongly influences susceptibility to E. coli bladder infections in C3H/HeJ mice.