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

• Published in: PLoS pathogens 2020-08, Vol.16 (8), p.e1008639-e1008639
• Main Authors: Bonhomme, Delphine, Santecchia, Ignacio, Vernel-Pauillac, Frédérique, Caroff, Martine, Germon, Pierre, Murray, Gerald, Adler, Ben, Boneca, Ivo G, Werts, Catherine
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Vesicular Transport - genetics; Adaptor Proteins, Vesicular Transport - metabolism; Animals; Antigens; Antiinfectives and antibacterials; Antimicrobial agents; Bacteriology; Biology and Life Sciences; Biosynthesis; CD14 antigen; Cellular signal transduction; Confocal microscopy; Cytokines - metabolism; Development and progression; E coli; Female; Flow cytometry; Health aspects; Immune response; Immune system; Immunology; Infections; Innate immunity; Internalization; Leptospira - immunology; Leptospirosis; Leptospirosis - immunology; Leptospirosis - metabolism; Leptospirosis - microbiology; Leptospirosis - pathology; Life Sciences; Lipids; Lipopolysaccharide Receptors - genetics; Lipopolysaccharide Receptors - metabolism; Lipopolysaccharides; Lipopolysaccharides - metabolism; Lipoproteins; Lipoproteins - genetics; Lipoproteins - metabolism; Macrophages; Male; Medicine and Health Sciences; Mice; Mice, Inbred C57BL; Microbiology and Parasitology; Microorganisms; MyD88 protein; Myeloid Differentiation Factor 88 - physiology; Nitric oxide; O antigen; O antigens; O Antigens - genetics; O Antigens - metabolism; Pattern recognition; Pattern recognition receptors; RANTES; Receptors; Research and Analysis Methods; Signal Transduction; Signaling; Structure; TLR2 protein; TLR4; TLR4 protein; Toll-Like Receptor 2 - physiology; Toll-Like Receptor 4 - physiology; Toll-like receptors; Vertebrates; Virulence
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/JOURNAL.PPAT.1008639

Leptospirosis is a worldwide re-emerging zoonosis caused by pathogenic Leptospira spp. All vertebrate species can be infected; humans are sensitive hosts whereas other species, such as rodents, may become long-term renal carrier reservoirs. Upon infection, innate immune responses are initiated by recognition of Microbial Associated Molecular Patterns (MAMPs) by Pattern Recognition Receptors (PRRs). Among MAMPs, the lipopolysaccharide (LPS) is recognized by the Toll-Like-Receptor 4 (TLR4) and activates both the MyD88-dependent pathway at the plasma membrane and the TRIF-dependent pathway after TLR4 internalization. We previously showed that leptospiral LPS is not recognized by the human-TLR4, whereas it signals through mouse-TLR4 (mTLR4), which mediates mouse resistance to acute leptospirosis. However, although resistant, mice are known to be chronically infected by leptospires. Interestingly, the leptospiral LPS has low endotoxicity in mouse cells and is an agonist of TLR2, the sensor for bacterial lipoproteins. Here, we investigated the signaling properties of the leptospiral LPS in mouse macrophages. Using confocal microscopy and flow cytometry, we showed that the LPS of L. interrogans did not induce internalization of mTLR4, unlike the LPS of Escherichia coli. Consequently, the LPS failed to induce the production of the TRIF-dependent nitric oxide and RANTES, both important antimicrobial responses. Using shorter LPS and LPS devoid of TLR2 activity, we further found this mTLR4-TRIF escape to be dependent on both the co-purifying lipoproteins and the full-length O antigen. Furthermore, our data suggest that the O antigen could alter the binding of the leptospiral LPS to the co-receptor CD14 that is essential for TLR4-TRIF activation. Overall, we describe here a novel leptospiral immune escape mechanism from mouse macrophages and hypothesize that the LPS altered signaling could contribute to the stealthiness and chronicity of the leptospires in mice.