In vitro effect of recombinant interferon gamma in combination with LPS on amoebicidal activity of murine Kupffer cells

Sex Difference in Amebiasis

Infection with the protozoan parasite Entamoeba histolytica is much more likely to cause severe, focal liver damage in males than females, although the infection rate is the same in both sexes. The differences in disease susceptibility may be due to modulation of key mechanisms of the innate immune response by sex hormones. Complement-mediated mechanisms and estrogen-dependent activated natural killer T cells lead to early elimination of the parasite in females, whereas a pathological immune axis is triggered in males. Testosterone, which is generally thought to have more immunosuppressive properties on cells of the immune response, leads to overwhelming activation of monocytes and host-dependent destruction of liver tissue in males resulting in worse outcomes.

Group 2 Innate Lymphoid Cells Exacerbate Amebic Liver Abscess in Mice

Entamoeba histolytica, a protozoan parasite in the lumen of the human large intestine, occasionally spreads to the liver and induces amebic liver abscesses (ALAs). Upon infection with E. histolytica, high levels of type 2 cytokines are induced in the liver early after infection. However, the sources and functions of these initial type 2 cytokines in ALA formation remain unclear. In this study, we examined the roles of group 2 innate lymphoid cells (ILC2s) in ALA formation. Hepatic ILC2 numbers were significantly increased and they produced robust levels of IL-5. The in vivo transfer of ILC2s into Rag2^−/−common γ chain (γ_c)^−/− KO mice aggravated ALA formation accompanied by eosinophilia and neutrophilia. Furthermore, IL-33-deficient mice and IL-5-neutralized mice had less ALA formations. These results suggest that ILC2s contribute to exacerbating the pathogenesis of ALA by producing early type 2 cytokines and promoting the accumulation of eosinophils and neutrophils in the liver.

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ILC2s exacerbate ALA by promoting the accumulation of eosinophils and neutrophils

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Hepatic ILC2s are increased and the main source of IL-5 in the early phase of ALA

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Hepatic ILC2s localize with IL-33⁺ cells in the inflammatory areas of ALA

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IL-33 is a trigger of ILC2-mediated ALA formation

Natural killer T cells activated by a lipopeptidophosphoglycan from Entamoeba histolytica are critically important to control amebic liver abscess

The innate immune response is supposed to play an essential role in the control of amebic liver abscess (ALA), a severe form of invasive amoebiasis due to infection with the protozoan parasite Entamoeba histolytica. In a mouse model for the disease, we previously demonstrated that Jalpha18(-/-) mice, lacking invariant natural killer T (iNKT) cells, suffer from more severe abscess development. Here we show that the specific activation of iNKT cells using alpha-galactosylceramide (alpha-GalCer) induces a significant reduction in the sizes of ALA lesions, whereas CD1d(-/-) mice develop more severe abscesses. We identified a lipopeptidophosphoglycan from E. histolytica membranes (EhLPPG) as a possible natural NKT cell ligand and show that the purified phosphoinositol (PI) moiety of this molecule induces protective IFN-gamma but not IL-4 production in NKT cells. The main component of EhLPPG responsible for NKT cell activation is a diacylated PI, (1-O-[(28:0)-lyso-glycero-3-phosphatidyl-]2-O-(C16:0)-Ins). IFN-gamma production by NKT cells requires the presence of CD1d and simultaneously TLR receptor signalling through MyD88 and secretion of IL-12. Similar to alpha-GalCer application, EhLPPG treatment significantly reduces the severity of ALA in ameba-infected mice. Our results suggest that EhLPPG is an amebic molecule that is important for the limitation of ALA development and may explain why the majority of E. histolytica-infected individuals do not develop amebic liver abscess.

Innate immunity prevents tissue invasion by Entamoeba histolytica

Although innate and adaptive immunity both play a role in amoebiasis, the mechanisms involved in the elimination of Entamoeba histolytica are poorly understood. To provide more information about the innate immune mechanisms that may confer protection against invasive amoebiasis, we administered inflammatory substances (bacillus Calmette-Guérin, lipopolysaccharide, complete Freund's adjuvant, or mineral oil) into the peritoneum of hamsters. The animals were then challenged with pathogenic trophozoites of E. histolytica and, after 7 days, the protective host response was analysed. We found that the nonspecific inflammatory response induced in the peritoneum was sufficient to prevent liver invasion by E. histolytica. In vitro experiments showed that the killing of trophozoites was mediated by peritoneal macrophages and a protein of 68 kDa with peroxidase activity.

Attenuated recombinant Yersinia as live oral vaccine carrier to protect against amoebiasis

Various attenuated Yersinia enterocolitica strains expressing different sections of the Entamoeba histolytica surface lectin via the type III protein secretion system (T3SS) were assessed for their use to orally vaccinate rodents against invasive amoebiasis. The T3SS was found to efficiently express and secrete or translocate subfragments as well as the entire heavy subunit of the lectin. Oral vaccination with recombinant Yersinia conferred significant protection against amoebic liver abscess formation when the antigen was expressed as a fusion molecule with the translocation domain of Yersinia outer protein E. However, effectiveness of vaccination was dependent on gender and the rodent species used. Protection was mediated primarily by cellular immune mechanisms as it was independent from the antibody titre against the amoeba lectin but correlated with an antigen-specific Th1-cytokine response. The results suggest that gram-negative bacteria expressing E. histolytica antigens via T3SS may constitute a suitable oral vaccine carrier against amoebiasis and that an effective IFN-gamma response is required for protection against invasive amoebiasis.

Oral vaccination with recombinant Yersinia enterocolitica expressing hybrid type III proteins protects gerbils from amebic liver abscess

Protection against invasive amebiasis was achieved in the gerbil model for amebic liver abscess by oral immunization with live attenuated Yersinia enterocolitica expressing the Entamoeba histolytica galactose-inhibitable lectin that has been fused to the Yersinia outer protein E (YopE). Protection was dependent on the presence of the YopE translocation domain but was independent from the antibody response to the ameba lectin.

Human amoebic hepatic abscess: in situ interactions between trophozoites, macrophages, neutrophils and T cells

Amoebic liver abscesses (ALA) are the most frequent and severe extraintestinal clinical presentations of amoebiasis. During the early establishment of amoebae in the liver parenchyma, as well as during the extension of the tissue necrosis, parasites interact with the parenchymal liver cells and, as a consequence of these interactions, hepatocytes can be destroyed and host immune cells can become activated. However, little is known about the nature of these interactions in the liver or about the factors involved in the local immune response. In this investigation we studied the localization of Entamoeba histolytica trophozoites, TCD4+, TCD8+ cells, CD68+ macrophages and CD15+ neutrophils in human ALA using immunohistochemical techniques. Trophozoites were found close to undamaged hepatocytes in both lysed and non-lysed areas with either sparse or abundant inflammatory infiltrate. CD8+ cells were more abundant than CD4+ T cells. CD 68+ macrophages and CD15+ neutrophils were also detected, suggesting that neutrophils, macrophages and T cells might be related to the local host immune mechanisms in ALA. We also found that E. histolytica possesses proteins recognized by antibodies raised against inducible nitric oxide synthase.

Prospect for an Entamoeba histolytica Gal-lectin-based vaccine

Entamoeba histolytica is the aetiological agent of invasive amoebiasis, the third leading parasitic cause of mortality in the world. The disease can be easily cured by chemotherapy; however, prevention, mainly in the form of vaccination, could greatly decrease the incidence of the disease, and possibly help in its eradication. The parasite's surface galactose and N-acetyl-d-galactosamine-inhibitable adherence lectin (Gal-lectin) is highly antigenic and is the most promising subunit vaccine candidate. We have generated a Gal-lectin-based DNA vaccine and tested its immunogenicity in mice. Although further optimization will probably be required, this vaccine could help in the generation of an amoebiasis DNA vaccine for use in humans.

Entamoeba histolytica: immunohistochemical study of hepatic amoebiasis in mouse. Neutrophils and nitric oxide as possible factors of resistance

Studies in mice have not rendered conclusive data on cell and humoral factors to support the resistance of this rodent to Entamoeba histolytica infection. In Balb/c and C3H/HeJ mice inoculated with live or fixed trophozoites, we studied the evolution of the hepatic lesion, the kinetics of inflammatory cells, and the participation of some humoral factors in the development of the hepatic amoebic lesion. From the first hour, amoebae were surrounded by neutrophils containing inducible nitric oxide synthase (iNOS); macrophages also expressing iNOS appeared lately, whereas NK cells were not part of the inflammatory infiltrates. On the fourth day, neutrophils, macrophages, T and B lymphocytes, plasma cells, and some NK cells limited the lesions and anti-amoeba antibodies appeared when most parasites had been eliminated. Therefore, the resistance of the mice to E. histolytica probably lies in non-specific immune responses, among which the activation of neutrophils and the production of nitric oxide (NO) may be important amoebicide factors.