# In vitro and in vivo endothelial interactions of Leptospira species are markers of virulence

## TL;DR

This study explores how different Leptospira bacteria interact with human cells and tissues, finding that certain interactions are linked to higher disease severity.

## Contribution

The study identifies endothelial cell interactions as potential markers of virulence in Leptospira species.

## Key findings

- High virulence Leptospira strains disrupt VE-cadherin in endothelial cells and induce strong immune responses.
- P1+ strains show significantly higher tissue burdens in mice compared to other Leptospira species.
- Bacterial association with host cells correlates with loss of VE-cadherin localization.

## Abstract

Leptospirosis is a global zoonotic disease caused by pathogenic species of the genus Leptospira. Leptospira species are classified into two major clades (pathogenic, P, and saprophytic, S), and four subclades (P1, P2, S1, and S2), with the P1 subclade further divided into high virulence (P1+) and low virulence (P1-) groups. While previous studies have associated P1 + species to greater virulence in the host, phenotypic characterization across clades, particularly regarding dissemination and cell barrier disruption, remains limited. In this study, sixteen strains of pathogenic and saprophytic Leptospira representing subclades P1 + , P1-, P2, and S1 were evaluated in vitro to assess association with human endothelial cells, disruption of host VE-cadherin localization in adherens junctions, and immune response as measured by cytokine and chemokine release. Our findings indicate that VE-cadherin disruption correlates with P1 + species and the presence of virulence-associated genes. Additionally, bacterial association with host cells correlates with the loss of VE-cadherin localization in adherens junctions. In vitro Leptospira interaction with endothelial cells induced production of chemokine and cytokines, most prominent in the P1 + clade and correlating with the presence of virulence-associated genes. Using an in vivo murine model of hematogenous dissemination to assess tissue tropism, live Leptospira were cultured from relevant tissues of animals inoculated with most of the strains tested and bacterial burdens were quantified to measure adhesion to tissues. Four of the six P1 + strains exhibited significantly higher tissue burdens in kidney, liver, and bladder at one hour post-inoculation compared to other Leptospira species. Together, these results suggest that endothelial cell interactions may be a key phenotypic marker for virulence classification in Leptospira. Further defining these interactions may therefore provide insights into interventions to combat this potentially fatal disease.

Leptospirosis is a global zoonotic disease and is transmitted to humans through contact with infectious bacteria found in the environment. In this study we tested sixteen strains of Leptospira, ranging from non-infectious to highly pathogenic species, in both cell culture and animal models. Disruption of cells and dissemination to tissues were associated with high virulence species. This study contributes to the understanding of Leptospira-host interactions, offers insights into the phenotypic diversity of Leptospira clades, and identifies phenotypes that can be used as virulence markers in future studies aimed at combatting this potentially fatal zoonotic disease.