Echinococcus granulosus Antigen B binds to monocytes and macrophages modulating cell response to inflammation

Abstract

BackgroundAntigen B (EgAgB) is an abundant lipoprotein released by the larva of the cestode Echinococcus granulosus into the host tissues. Its protein moiety belongs to the cestode-specific family known as hydrophobic ligand binding protein (HLBP), and is encoded by five gene subfamilies (EgAgB8/1-EgAgB8/5). The functions of EgAgB in parasite biology remain unclear. It may play a role in the parasite’s lipid metabolism since it carries host lipids that E. granulosus is unable to synthesise. On the other hand, there is evidence supporting immuno-modulating activities in EgAgB, particularly on innate immune cells. Both hypothetical functions might involve EgAgB interactions with monocytes and macrophages, which have not been formally analysed yet.MethodsEgAgB binding to monocytes and macrophages was studied by flow cytometry using inflammation-recruited peritoneal cells and the THP-1 cell line. Involvement of the protein and phospholipid moieties in EgAgB binding to cells was analysed employing lipid-free recombinant EgAgB subunits and phospholipase D treated-EgAgB (lacking the polar head of phospholipids). Competition binding assays with plasma lipoproteins and ligands for lipoprotein receptors were performed to gain information about the putative EgAgB receptor(s) in these cells. Arginase-I induction and PMA/LPS-triggered IL-1β, TNF-α and IL-10 secretion were examined to investigate the outcome of EgAgB binding on macrophage response.ResultsMonocytes and macrophages bound native EgAgB specifically; this binding was also found with lipid-free rEgAgB8/1 and rEgAgB8/3, but not rEgAgB8/2 subunits. EgAgB phospholipase D-treatment, but not the competition with phospholipid vesicles, caused a strong inhibition of EgAgB binding activity, suggesting an indirect contribution of phospholipids to EgAgB-cell interaction. Furthermore, competition binding assays indicated that this interaction may involve receptors with affinity for plasma lipoproteins. At functional level, the exposure of macrophages to EgAgB induced a very modest arginase-I response and inhibited PMA/LPS-mediated IL-1β and TNF-α secretion in an IL-10-independent manner.ConclusionEgAgB and, particularly its predominant EgAgB8/1 apolipoprotein, are potential ligands for monocyte and macrophage receptors. These receptors may also be involved in plasma lipoprotein recognition and induce an anti-inflammatory phenotype in macrophages upon recognition of EgAgB.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1350-7) contains supplementary material, which is available to authorized users.

Characterisation of Antigen B Protein Species Present in the Hydatid Cyst Fluid of Echinococcus canadensis G7 Genotype

“…Since AgB likely contributes to the mechanisms used by the metacestode to transport lipids, particularly those that the parasite is unable to synthesise, this result would indicate that AgB8/1 is the main AgB apolipoprotein involved in this transport, and, in consequence, the presence of AgB8/1 receptors in parasite and host cells is worth to be further studied. To this respect, AgB8/1 was found to bind selectively to monocyte and macrophages, but the molecular partners involved have not been identified yet [41]. Furthermore, we identified an additional Echinococcus HLBP (EgrG_000549200) and host apolipoproteins (particularly Apo A-I) in QS f , which suggests that several lipid carriers are involved in parasite mechanisms aimed at providing essential lipids to metacestode tissues.…”

“…However, to achieve an adequate sample for AgB apolipoprotein characterisation, we firstly carried out an enrichment step since AgB is poorly represented in HF compared to host albumin and immunoglobulins. Taking advantage that AgB can be selectively separated from these host proteins employing a Mono-Q [40] or Q-Sepharose beads [41], we prepared an AgB enriched-fraction by a single step anion exchange chromatography of HF on Q-Sepharose; this step concentrates AgB favouring the detection of lower represented apolipoproteins. S1 Fig shows the SDS-PAGE analysis of fractions obtained by this chromatography.…”

Granulomatous responses in larval taeniid infections

“…In terms of cell recruitment, TNF‐α secretion is inhibited by a low molecular mass RNA peptide from T. solium metacestodes and by the lipoprotein “antigen B” from E. granulosus . Also, E. multilocularis metacestodes secrete a proteinase capable of digesting eotaxin, a major eosinophil chemoattractant …”

Antigen B from Echinococcus granulosus enters mammalian cells by endocytic pathways

“…http://dx.doi.org/10.1101/224691 doi: bioRxiv preprint first posted online Nov. 24, 2017; 5 should occur. In fact, it was recently demonstrated that AgB binds to macrophages and the 97 plasma membrane of inflammatory monocytes, inducing a non-inflammatory phenotype in 98 macrophages [21]. However, little is known about the molecular details of AgB-cell 99 interaction and whether AgB interacts with non-immune cells, or even enters into the cell.…”

“…It was proposed that AgB binds to macrophages and monocytes plasma 373 membranes through a lipoprotein receptor; however no specific receptor could be 374 determined [21]. Our findings are in agreement with this idea because some lipoprotein 375 receptors, such as lectin-like oxidized LDL receptor-1 (LOX-1), LDL receptor-related 376 protein 6 (LRP6), and scavenger receptors CD36 and CD204 use raft-mediated pathways 377 for endocytosis [33][34][35][36].…”