Role of TLR4 in Persistent Leptospira interrogans Infection: A Comparative In Vivo Study in Mice.

Nisha Nair,Catherine Werts,Maria Gomes-Solecki,Adeline M Hajjar,Mariana S Guedes

doi:10.3389/fimmu.2020.572999

Abstract

Toll-Like Receptor (TLR) 4, the LPS receptor, plays a central role in the control of leptospirosis and absence of TLR4 results in lethal infection in mice. Because human TLR4 does not sense the atypical leptospiral-LPS, we hypothesized that TLR4/MD-2 humanized transgenic mice (huTLR4) may be more susceptible to leptospirosis than wild-type mice, and thus may constitute a model of acute human leptospirosis. We infected huTLR4 mice, which express human TLR4 but not murine TLR4, with a high dose of L. interrogans serovar Copenhageni FioCruz (Leptospira) in comparison to C57BL/6J wild-type (WT) and, as a control, a congenic strain in which the tlr4 coding sequences are deleted (muTLR4Lps-del). We show that the huTLR4 gene is fully functional in the murine background. We found that dissemination of Leptospira in blood, shedding in urine, colonization of the kidney and overall kinetics of leptospirosis progression is equivalent between WT and huTLR4 C57BL/6J mice. Furthermore, inflammation of the kidney appeared to be subdued in huTLR4 compared to WT mice in that we observed less infiltrates of mononuclear lymphocytes, less innate immune markers and no relevant differences in fibrosis markers. Thus, huTLR4 mice showed less inflammation and kidney pathology, and are not more susceptible to leptospirosis than WT mice. This study is significant as it indicates that one intact TLR4 gene, be it mouse or human, is necessary to control acute leptospirosis.

Highlights

Leptospira spp (Leptospira) are not considered gram-negative bacteria but they produce lipopolysaccharide (LPS), a potent inflammatory cell wall component that has been shown to be less inflammatory in Leptospira
To find out if replacing the murine TLR4 with human TLR4 affects the kinetics of leptospirosis progression, we compared infection in wild-type C57BL/6J (WT) and humanized TLR4/ MD2 transgenic mice and added a congenic murine mutant lacking the TLR4 receptor as control
When we quantified the burden of Leptospira in fluids and tissues by qPCR we found low numbers of Leptospira in blood in WT and humanized TLR4/ MD2 transgenic mice (huTLR4) mice and, as expected, a significantly higher number of Leptospira in muTLR4 Lps-del (Figure 2A)

Summary

Introduction

Leptospira spp (Leptospira) are not considered gram-negative bacteria but they produce lipopolysaccharide (LPS), a potent inflammatory cell wall component that has been shown to be less inflammatory in Leptospira. Researchers working on the function of the host TLR4 in leptospirosis used immunocompetent C57BL/6J and its respective congenic TLR4 knockouts They found that wildtype (WT) mice expressing competent TLR4 receptors in their immune cells are resistant to lethal infection with L. interrogans whereas TLR4 knockouts are susceptible, have larger numbers of Leptospira in tissues and succumb to infection [4]. We and others [5,6,7,8] developed mouse models of lethal and sublethal leptospirosis using C3H-HeJ mice that have a point mutation in the cytoplasmic domain of the tlr gene [9] These data strongly suggest that the competence of the TLR4 receptor affects leptospirosis outcomes

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