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PLoS Pathog. 2009 May;5(5):e1000434. doi: 10.1371/journal.ppat.1000434. Epub 2009 May 15.

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

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Bernhard-Nocht-Institute for Tropical Medicine, Hamburg, Germany.


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.

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