Neutralizing gut-derived lipopolysaccharide as a novel therapeutic strategy for severe leptospirosis

Leptospirosis is an emerging infectious disease caused by pathogenic Leptospira spp. Humans and some mammals can develop severe forms of leptospirosis accompanied by a dysregulated inflammatory response, which often results in death. The gut microbiota has been increasingly recognized as a vital element in systemic health. However, the precise role of the gut microbiota in severe leptospirosis is still unknown. Here, we aimed to explore the function and potential mechanisms of the gut microbiota in a hamster model of severe leptospirosis. Our study showed that leptospires were able to multiply in the intestine, cause pathological injury, and induce intestinal and systemic inflammatory responses. 16S rRNA gene sequencing analysis revealed that Leptospira infection changed the composition of the gut microbiota of hamsters with an expansion of Proteobacteria. In addition, gut barrier permeability was increased after infection, as reflected by a decrease in the expression of tight junctions. Translocated Proteobacteria were found in the intestinal epithelium of moribund hamsters, as determined by fluorescence in situ hybridization, with elevated lipopolysaccharide (LPS) levels in the serum. Moreover, gut microbiota depletion reduced the survival time, increased the leptospiral load, and promoted the expression of proinflammatory cytokines after Leptospira infection. Intriguingly, fecal filtration and serum from moribund hamsters both increased the transcription of TNF-α, IL-1β, IL-10, and TLR4 in macrophages compared with those from uninfected hamsters. These stimulating activities were inhibited by LPS neutralization using polymyxin B. Based on our findings, we identified an LPS neutralization therapy that significantly improved the survival rates in severe leptospirosis when used in combination with antibiotic therapy or polyclonal antibody therapy. In conclusion, our study not only uncovers the role of the gut microbiota in severe leptospirosis but also provides a therapeutic strategy for severe leptospirosis.

IL-10 Deficiency Protects Hamsters from Leptospira Infection

Leptospirosis is a global zoonotic disease with outcomes ranging from subclinical infection to fatal Weil's syndrome. In addition to antibiotics, some immune activators have shown protective effects against leptospirosis. However, the unclear relationship between Leptospira and cytokines has limited the development of antileptospiral immunomodulators. In this study, the particular role of interleukin-10 (IL-10) in leptospirosis was explored by using IL-10-defective (IL-10-/-) hamsters. After Leptospira infection, an improved survival rate, reduced leptospiral burden, and alleviation of organ lesions were found in IL-10-/- hamsters compared with wild-type (WT) hamsters. In addition, the levels of expression of the IL-1β, IL-6, and tumor necrosis factor alpha (TNF-α) genes and the level of nitric oxide (NO) were higher in IL-10-/- hamsters than in WT hamsters. Our results indicate that IL-10 deficiency protects hamsters from Leptospira infection.

Immune-enhanced effect of Iris polysaccharide is protective against leptospirosis

Leptospirosis, caused by pathogenic Leptospira species, is an essential but neglected zoonosis. There are more than 300 serovars of pathogenic Leptospira, while inactivated bacteria offers only short-term serovar-specific protection. Leptospirosis treatment is mainly dependent on the use of antibiotics. However, the side effects of antibiotics and the risk of antibiotic resistance remain major problems. Thus, alternative agents which are fewer side effects on humans and efficient in leptospirosis would be welcome. Many studies have reported that polysaccharides could be used as immunostimulants in treating infection and cancer. In this study, we examined the protective effect of polysaccharides isolated from Iris against leptospirosis. To our knowledge, it is the first time to report Iris polysaccharides (IP) as an immunostimulant in treating infection. The results showed that IP treatment significantly increased the survival rate of hamsters challenged by a lethal dose of leptospires. Besides, the tissue injury and leptospiral load were reduced in IP-treated infection group compared with the untreated infection group at 4 days post-infection (p.i.). Intriguingly, IP treatment sustained intense immune response at 4 days p.i. analyzed by qPCR. The results exhibited that the gene expression of TLR2 and TLR4 was significantly increased in the group coinjected with IP and leptospires than in the infected controls. And the expression of IL-1β and TNF-α were also up-regulated after IP treatment, except the expression of IL-1β in the kidney. Our results not only broaden the medicinal value of Iris, but also provide a competent candidate for the control of Leptospira infection.

The pre-activated immune response induced by LPS protects host from leptospirosis

Leptospirosis is an important global zoonosis caused by pathogenic Leptospira. It is estimated that more than 1 million people are infected by Leptospira each year, and the death toll is about 60,000. Some studies showed that delayed immune response was associated with severe leptospirosis, and TLR4 was very important in the control of leptospirosis. In this study, we aimed to explore the effect of the classical activator (LPS) of TLR4 on leptospirosis in susceptible and resistant hosts. The results showed that LPS pretreatment increased the survival rate of hamsters to 80%. And LPS pre-treatment also significantly reduced the leptospiral load and alleviated the pathological injury in organs of hamsters and mice. The result detected by ELISA in mice showed that the levels of TNF-α and IL-1β were increased in the LPS-treated group compared to the control group before infection. However, two days after infection, the level of cytokines in LPS group was down-regulated compared with that in control group. In addition, in vitro results showed that LPS pre-treatment enhanced the phagocytosis and bactericidal ability of macrophages on Leptospira. Collectively, our results indicated that the pre-activated immune response induced by LPS enhanced the ability of host against leptospirosis.

Increased inflammation with crude E. coli LPS protects against acute leptospirosis in hamsters

Leptospirosis is a worldwide zoonotic disease that causes acute kidney injury, liver disease, bleeding disorders, and even death. Treatment of the disease is largely dependent on the use of antibiotics, but recent studies on pathogenesis of leptospirosis have shown that immunomodulation may also be an effective treatment for this disease. Since the delay in inflammation correlates with higher pathogenicity of leptospira, we studied the effect of inducing inflammation on leptospirosis by using TLR4 activator LPS. In accordance with our hypothesis, treatment with LPS protected against leptospirosis by enhancing the inflammatory response in hamsters. The gene expression levels of TLR2, TLR4, NLRP3 and inflammatory factors were higher in LPS-treated group during leptospira infection in hamsters. Although the levels of NO and iNOS were higher in LPS-treated group than in Leptospira-infected group, the protective effect induced by LPS is iNOS-independent. Treatment with LPS induced higher anti-leptospira IgG level than infection with leptospira alone. Then, expressions of costimulatory molecules and maturation markers were analysed. The data showed that treatment with LPS enhanced the expression of CD40, CD80 and CD86. Our results indicate that increased inflammation induced by LPS derived from Escherichia coli (E. coli) protects against leptospirosis in hamsters.

Doxycycline Attenuates Leptospira-Induced IL-1β by Suppressing NLRP3 Inflammasome Priming

Doxycycline (Dox), a semisynthetic antibiotic, has been reported to exert multiple immunomodulatory effects. Treatment with Dox has a satisfactory curative effect against leptospirosis. In addition to its antibacterial action, we supposed that Dox also modulated immune response in controlling leptospira infection. Using J774A.1 mouse macrophages, the effects of Dox on protein and mRNA levels of IL-1β and TNF-α were investigated after infection with live or sonicated Leptospira interrogans serovar Lai strain Lai (56601). Specifically, the level of IL-1β but not TNF-α was sharply decreased when treated with Dox in leptospira-infected macrophages. Western blot analysis showed that Dox suppressed the activation of leptospira-induced MAPK and NF-κB signaling pathways. Using NLRP3-deficient and NLRC4-deficient mice, the data showed that the expression of leptospira-induced IL-1β was mainly dependent on the presence of NLRP3 inflammasome in macrophages. Meanwhile, Dox suppressed leptospira-induced NLRP3 inflammasome priming with the upregulation of the Na/K-ATPase Pump β1 subunit. The inhibition effect of Dox on IL-1β was also conspicuous in cells with lipopolysaccharide and ATP stimulation. These results were confirmed in vivo, as peritoneal fluids of mice and organs of hamsters expressed less IL-1β after treatment of leptospiral infection with Dox. Our results indicated that Dox also modulated immune response to attenuate leptospira-induced IL-1β by suppressing p38, JNK, p65, and NLRP3 inflammasome priming.