The Glycosyl-Inositol-Phosphate and Dimyristoylglycerol Moieties of the Glycosylphosphatidylinositol Anchor of the Trypanosome Variant-Specific Surface Glycoprotein Are Distinct Macrophage-Activating Factors

Abstract

The TNF-α-inducing capacity of different trypanosome components was analyzed in vitro, using as indicator cells a macrophage cell line (2C11/12) or peritoneal exudate cells from LPS-resistant C3H/HeJ mice and LPS-sensitive C3H/HeN mice. The variant-specific surface glycoprotein (VSG) was identified as the major TNF-α-inducing component present in trypanosome-soluble extracts. Both soluble (sVSG) and membrane-bound VSG (mfVSG) were shown to manifest similar TNF-α-inducing capacities, indicating that the dimyristoylglycerol (DMG) compound of the mfVSG anchor was not required for TNF-α triggering. Detailed analysis indicated that the glycosyl-inositol-phosphate (GIP) moiety was responsible for the TNF-α-inducing activity of VSG and that the presence of the GIP-associated galactose side chain was essential for optimal TNF-α production. Furthermore, the results showed that the responsiveness of macrophages toward the TNF-α-inducing activity of VSG was strictly dependent on the activation state of the macrophages, since resident macrophages required IFN-γ preactivation to become responsive. Comparative analysis of the ability of both forms of VSG to activate macrophages revealed that mfVSG but not sVSG stimulates macrophages toward IL-1α secretion and acquisition of LPS responsiveness. The priming activity of mfVSG toward LPS responsiveness was also demonstrated in vivo and may be relevant during trypanosome infections, since Trypanosoma brucei-infected mice became gradually LPS-hypersensitive during the course of infection. Collectively, the VSG of trypanosomes encompasses two distinct macrophage-activating components: while the GIP moiety of sVSG mediates TNF-α induction, the DMG compound of the mfVSG anchor contributes to IL-1α induction and LPS sensitization.

Roles of cytokines in modulating Trypanosoma brucei rhodesiense infection outcomes in vervet monkeys

“…Also necessary are pathogen factors that act as exogenous pyrogens, whose detection by resident innate immune cells elicit IL-1 and IL-6 production, and also activate PGE2 synthesis 69 . Trypanosome glycosylphosphatidylinositol (GPI) is a prime candidate exogenous pyrogen, having been shown by others [70][71][72] to elicit production of innate cytokines, including IL-6. The higher levels of IL-6 in infected cohorts (Table 2; Figure 4E) could explain the increase to core body temperature, while differences in febrile responses between acute and chronic infections could be due to strain-related varying levels of fever mediators.…”

Pathogenicity and virulence of African trypanosomes: From laboratory models to clinically relevant hosts

“…Whereas IFN- γ exposure followed by sVSG exposure leads to the expression of TNF-α, IL-6, and IL12p40, treatment of macrophages with sVSG prior to IFN-γ led to a reduction in IFN-γ-induced responses, including reduced NO synthase expression and NO secretion [ 165 ]. Further work showed that the glycosylinositolphosphate moiety of the sVSG is crucial for these host modulatory effects [ 165 , 166 ].…”

The Function of Phosphatidylinositol 3-Kinase delta (PI3Kδ) Enzyme in Protective Immunity to Trypanosoma congolense Infection in Mice: The Role of Regulatory B cells

“…These cells are reported as being the first line of defence against the parasite and their components, following the invasion of the host. It is reported that to trigger the innate immune response to the parasite, the glycosylphosphatidylinositol (GPI) that anchors the parasite's surface protein, the variant surface glycoprotein (VSG) needs to interact with pattern recognition receptors (PRR) such as CD14 on monocytic cells, to cause the activation of these cells and permit the simultaneous release of proinflammatory cytokines 29,32 .…”