Cagliero, J. | bioRxiv Science

bioRxiv2026

β-lactam antibiotics trigger TLR2-dependent Jarisch-Herxheimer reaction in leptospirosis: bacteriostatic antibiotics offer a safer alternative

Leptospirosis is a neglected zoonotic disease causing ~1 million cases and 60,000 deaths annually. Antibiotic therapy can trigger a detrimental inflammatory Jarisch-Herxheimer reaction (JHR). We investigated antibiotic effects in leptospirosis, using a mouse model of severe disease and human whole blood from healthy donors infected ex vivo with bioluminescent Leptospira interrogans. We tested the effect of amoxicillin and ceftriaxone, two bactericidal beta-Lactams antibiotics and assessed bacterial survival, cytokines, pathophysiology and JHR mechanisms upon amoxicillin. Beta-lactams induced profound pro-inflammatory cytokine release. In mice, the inflammation was TLR2 and TLR4 dependent, accordingly to the TLR4 host-specificity of LPS recognition, and amoxicillin exacerbated disease severity within hours, notably worsening myocarditis. In human whole blood, this inflammation depended largely on TLR2 (lipoprotein receptor) and TLR5 (flagellin receptor). Interestingly, only stealthy virulent isolates of Leptospira interrogans, unlike some Leptospira species belonging to intermediate and non-virulent clades such as biflexa, induced in human whole blood a JHR-like effect, which was also observed with Borrelia burgdorferi. These findings demonstrate that host-specific TLR recognition of released spirochaetal components by antibiotic treatment drives JHR, evoking a cytokine storm and worsening outcomes.

immunology↗

bioRxiv2020

Escape of TLR5 Recognition by Leptospira spp: A Rationale for Atypical Endoflagella

Leptospira interrogans are invasive bacteria responsible for leptospirosis, a worldwide zoonosis. They possess two periplasmic endoflagella that allow their motility. L. interrogans are stealth pathogens that escape the innate immune responses of the NOD-like receptors NOD1/2, and the human Toll-like receptor (TLR)4, sensing peptidoglycan and lipopolysaccharide (LPS), respectively. TLR5 is another receptor of bacterial cell wall components, recognizing flagellin subunits. To study the contribution of TLR5 in the host defense against leptospires, we infected WT and TLR5 deficient mice with pathogenic L. interrogans and tracked the infection by in vivo live imaging of bioluminescent bacteria or by q-PCR. We did not identify any protective or inflammatory role of murine TLR5 to control pathogenic Leptospira. Likewise, subsequent in vitro experiments showed that infections with different live strains of L. interrogans and L. biflexa did not trigger TLR5. However, unexpectedly, heat-killed bacteria stimulated human and bovine TLR5, although barely mouse TLR5. Abolition of TLR5 recognition required extensive boiling time of the bacteria or proteinase K treatment, showing an unusual high stability of the leptospiral flagellins. Interestingly, using antimicrobial peptides to destabilize live leptospires, we detected some TLR5 activity, suggesting that TLR5 could participate in the fight against leptospires in humans or cattle. Using different Leptospira strains with mutations in flagellin proteins, we further showed that neither FlaAs nor Fcps participated in the recognition by TLR5, suggesting a role for the FlaBs. These have structural homology to Salmonella FliC, and conserved residues important for TLR5 activation, as shown by in silico analyses. Accordingly, we found that leptospires regulate the expression of FlaB mRNA according to the growth phase in vitro, and that infection with L. interrogans in hamsters and in mice downregulated the expression of the FlaBs but not the FlaAs subunits. Altogether, in contrast to different bacteria that modify their flagellin sequences to escape TLR5 recognition, our study suggests that the peculiar central localization and stability of the FlaB monomers in the periplasmic endoflagella, associated with the downregulation of FlaB subunits in hosts, constitute an efficient strategy of leptospires to escape TLR5 recognition and the immune response.

immunology↗