Institut Pasteur de Nouvelle-Calédonie, member of the Pasteur Network, Immunity and Inflammation Group (GIMIN), Noumea, New Caledonia.
Institut Pasteur, Université de Paris, CNRS UMR6047, INSERM U1306, Unité de Biologie et Génétique de la Paroi bactérienne, F-75015 Paris, France.
Front Immunol. 2022 Jun 22;13:911778. doi: 10.3389/fimmu.2022.911778. eCollection 2022.
is a bacterial species responsible for leptospirosis, a neglected worldwide zoonosis. Mice and rats are resistant and can become asymptomatic carriers, whereas humans and some other mammals may develop severe forms of leptospirosis. Uncommon among spirochetes, leptospires contain lipopolysaccharide (LPS) in their outer membrane. LPS is highly immunogenic and forms the basis for a large number of serovars. Vaccination with inactivated leptospires elicits a protective immunity, restricted to serovars with related LPS. This protection that lasts in mice, is not long lasting in humans and requires annual boosts. Leptospires are stealth pathogens that evade the complement system and some pattern recognition receptors from the Toll-like (TLR) and Nod-Like families, therefore limiting antibacterial defense. In macrophages, leptospires totally escape recognition by human TLR4, and escape the TRIF arm of the mouse TLR4 pathway. However, very little is known about the recognition and processing of leptospires by dendritic cells (DCs), although they are crucial cells linking innate and adaptive immunity. Here we tested the activation of primary DCs derived from human monocytes (MO-DCs) and mouse bone marrow (BM-DCs) 24h after stimulation with saprophytic or different pathogenic virulent or avirulent . We measured by flow cytometry the expression of DC-SIGN, a lectin involved in T-cell activation, co-stimulation molecules and MHC-II markers, and pro- and anti-inflammatory cytokines by ELISA. We found that exposure to leptospires, live or heat-killed, activated dendritic cells. However, pathogenic , especially from the Icterohaemorraghiae Verdun strain, triggered less marker upregulation and less cytokine production than the saprophytic . In addition, we showed a better activation with avirulent leptospires, when compared to the virulent parental strains in murine BM-DCs. We did not observe this difference in human MO-DCs, suggesting a role for TLR4 in DC stimulation. Accordingly, using BM-DCs from transgenic deficient mice, we showed that virulent Icterohaemorraghiae and Manilae serovars dampened DC activation, at least partly, through the TLR4 and TRIF pathways. This work shows a novel bacterial immune evasion mechanism to limit DC activation and further illustrates the role of the leptospiral LPS as a virulence factor.
是一种引起钩端螺旋体病的细菌，这种疾病是一种被忽视的全球性动物传染病。老鼠和大鼠对其具有抵抗力，并且可能成为无症状的带菌者，而人类和其他一些哺乳动物则可能发展出严重的钩端螺旋体病。与其他螺旋体不同的是，钩端螺旋体的外膜含有脂多糖（LPS）。LPS 具有高度的免疫原性，是大量血清型的基础。用灭活的钩端螺旋体进行疫苗接种可产生针对相关 LPS 的血清型的保护性免疫。这种在小鼠中持续存在的保护作用在人类中并不持久，需要每年加强。钩端螺旋体是一种隐秘的病原体，它可以逃避补体系统和 Toll 样（TLR）和 Nod 样家族中的一些模式识别受体，从而限制了抗菌防御。在巨噬细胞中，钩端螺旋体完全逃避了人 TLR4 的识别，也逃避了小鼠 TLR4 途径中的 TRIF 分支。然而，对于树突状细胞（DC）识别和处理钩端螺旋体的情况，我们知之甚少，尽管它们是连接先天免疫和适应性免疫的关键细胞。在这里，我们检测了源自人单核细胞（MO-DCs）和小鼠骨髓（BM-DCs）的原代 DCs 在刺激 24 小时后的激活情况，刺激物包括腐生或不同致病性的强毒或弱毒株。我们通过流式细胞术测量了 DC-SIGN 的表达，DC-SIGN 是一种参与 T 细胞激活的凝集素，还测量了共刺激分子和 MHC-II 标志物以及促炎和抗炎细胞因子的表达情况，这些细胞因子的表达情况通过 ELISA 进行测量。我们发现，暴露于活的或热灭活的钩端螺旋体可激活树突状细胞。然而，致病性的，特别是来自伊氏出血性黄疸 Verdun 株的钩端螺旋体，其标志物上调和细胞因子产生的水平低于腐生的。此外，与强毒株的亲本株相比，我们发现弱毒株能更好地激活鼠源 BM-DCs。然而，我们没有在人源 MO-DCs 中观察到这种差异，这表明 TLR4 在 DC 刺激中起作用。因此，使用来自 TLR4 缺陷型转基因小鼠的 BM-DCs，我们发现强毒伊氏出血性黄疸和 Manilae 血清型通过 TLR4 和 TRIF 途径抑制了 DC 的激活，至少部分如此。这项工作揭示了一种新的细菌免疫逃避机制，可限制 DC 的激活，并进一步说明了钩端螺旋体 LPS 作为一种毒力因子的作用。
