A new model of self-resolving leptospirosis in mice infected with a strain of Leptospira interrogans serovar Autumnalis harboring LPS signaling only through TLR4

Abstract

Leptospirosis is an emerging worldwide zoonosis caused by pathogenic Leptospira spp. Our understanding of leptospirosis pathogenesis and host immune response remains limited, while mechanistic studies are hindered by a lack of proper animal models and immunological reagents. Here we established a murine model of acute and self-resolving leptospirosis by infecting 10-week-old C57BL/6 mice with Leptospira interrogans serovar Autumnalis strain 56606v, with characteristic manifestations including jaundice as well as subcutaneous and pulmonary bleeding, but no kidney lesions. We also verified that the lipopolysaccharide (LPS) of strain 56606v signaled through a TLR4-dependent pathway in murine bone marrow-derived macrophages (BMDMs), rather than the previously reported TLR2. In addition, upon infection with Leptospira strain 56606v, TLR4−/− C57BL/6 mice presented more severe jaundice and liver injury as well as higher bacterial loads than WT mice but milder pulmonary hemorrhaging. Molecular studies showed that leptospirosis-related bleeding coincides with the temporal kinetics of iNOS production, while jaundice and liver injury are probably due to insufficiently controlled bacterial loads in the liver. These results suggested that TLR4 is essential in mediating host leptospiral clearance and, to some extent, is associated with pulmonary and subcutaneous hemorrhage, probably through downstream inflammatory mediators, iNOS in particular. Overall, our murine model using immunocompetent mice might facilitate future studies into the pathogenesis of jaundice and bleeding in leptospirosis. Meanwhile, our study suggests the prospect of combining antibiotics and immunosuppressants in the treatment of severe leptospirosis presenting with pulmonary hemorrhage.

Leptospiral LPS escapes mouse TLR4 internalization and TRIF-associated antimicrobial responses through O antigen and associated lipoproteins

“…Although leptospiral LPS is recognized by the mTLR4, we described here that in vitro it escapes the TRIF arm of the TLR4 response, hence dodging antimicrobial responses. Accordingly, other study [65] has demonstrated that such mechanism is relevant in vivo . The novelty of the present work resides in the study of the signaling properties of the leptospiral LPS in its “crude” form, and investigation of the role played by the physiologically relevant copurifying lipoproteins.…”

“…Furthermore, we showed that infection of macrophages with the leptospiral mutant induced more NO than the parental strain. Accordingly, it was recently shown that L. interrogans serovar Autumnalis strain 56606v, which possesses an LPS atypically signaling only through TLR4 [65], leads to a self-resolving leptospirosis in mice. To our knowledge, besides the Patoc LPS described here, this is the first evidence of a leptospiral LPS naturally devoid of TLR2 activity.…”

“…To our knowledge, besides the Patoc LPS described here, this is the first evidence of a leptospiral LPS naturally devoid of TLR2 activity. Upon infection with that specific leptospiral strain, TLR4 was shown to be essential to the resolution of the infection, and authors described a TLR4-dependent iNOS activation that they hypothesize could contribute to the leptospiral clearance by the host [65]. Altogether, these findings suggest that full length O antigen of the LPS and co-purifying lipoproteins contribute to the dampening of the TRIF signaling and potentially participate in the stealthiness of the leptospires.…”

Recent findings related to immune responses against leptospirosis and novel strategies to prevent infection

“…A recent predictive structural study using truncated Lip32 proteins suggests that the complex formation depends on a hydrophobic interaction [34]. Interestingly, one study highlighted that the LPS of L. interrogans serovar Autumnalis strain 56606 only signals through murine TLR4, and not through TLR2 [35]. The authors showed in a TLR4KO mouse model that this strain induces a mild self-resolving acute leptospirosis, affecting liver and lungs with no association to kidney lesions [35].…”

Toll‐like receptors: The role in bladder cancer development, progression and immunotherapy

“…TLR2 ligands include glycoinositolphospholipids, glycolipids, lipoarabinomannan (LAM), atypical LPS, lipoteichoic acid, peptidoglycans, porins and heat shock proteins (HSPs) for recognition of UTIs due to microbial pathogens.…”