Outcomes of Leptospira interrogans Infection in C3H/HeJ and C3H/HeN Mice Strains

Leptospirosis is a significant, underrecognized global zoonosis caused by Leptospira. The C3H/HeJ mouse is a well-recognized lab animal model for Leptospira studies due to the strain’s spontaneous mutation in the toll-like receptor 4 (Tlr4) gene and ability to develop leptospirosis. However, the full characterization of Leptospira infection in the C3H/HeJ model in comparison to its wild type, C3H/HeNHsd (C3H/HeN), is not available. The objective of this study was to compare the outcomes of Leptospira interrogans serovar Manilae infection in C3H/HeJ and C3H/HeN mice. Eight-week-old male and female mice (n = 8) from the strains C3H/HeJ and C3H/HeN were intraperitoneally infected with 6x106 cells Leptospira interrogans serovar Manilae strain L495. An uninfected group (n = 4) from each strain was kept as negative controls. Mice were observed daily post-infection to evaluate clinical scores and were humanely euthanized at Institutional Animal Care and Use Committee (IACUC)-approved endpoints. Heart, lung, liver, spleen, kidneys, and blood were collected for evaluating organ weights and histopathology, Leptospira colonization (PCR and culture), host response (enzyme-linked immunosorbent assay (ELISA) and microscopic agglutination test (MAT), and cytokine evaluation), transcriptomics, and metabolomics. All infected C3H/HeJ and C3H/HeN mice were susceptible to leptospirosis. The C3H/HeN strain had a higher IgM and IgG response after infection compared to the C3H/HeJ strain, and more agglutination was seen in the infected C3H/HeN group. Pro-inflammatory and macrophage-related cytokines were found in statistically significant levels in the spleen, kidneys, liver, and serum. All organs from infected mice were determined as positive via qPCR and culture. Leptospira infection was not detected in control mice. More pro-inflammatory- and macrophage-related transcripts were upregulated in infected C3H/HeN mice compared to C3H/HeJ mice, but the metabolite profiles of both mice strains were similar. The C3H/HeN strain had been previously described as resistant to leptospirosis, but overall, our study showed there are little differences in the outcomes of Leptospira interrogans serovar Manilae infection in C3H/HeN mice when compared to C3H/HeJ mice.