Echinococcus granulosus antigen B: a parasite lipoprotein with immunoregulatory and lipid acquisition properties in myeloid cells

Abstract

The larval stage of Echinococcus granulosus, responsible for cystic echinococcosis, establishes a chronic infection that tightly modulates host immunity. Adapted to a nutrient-rich environment, the parasite has lost its de novo synthesis of fatty acids and cholesterol, relying on host-derived lipids via specialized proteins. Antigen B (EgAgB), the main larval lipoprotein belonging to the cestode-specific hydrophobic ligand-binding proteinfamily, is exported to host tissues and resembles HDL in physicochemical properties and anti-inflammatory actions on innate cells. Our investigation on EgAgB´s biological activities revealed that both native and recombinant lipoproteins induced a modest dendritic cell (DC) activation, attributed to LPS contamination, while suppressing LPS- induced cytokine (IL1beta, IL6, IL12, IFNbeta) and nitric oxide production in DC and macrophages (MQ) by disrupting TLR4 dimerization. In the current work, we confirmed that in an LPS stimulation context EgAgB does not affect ATP potentiation of IL1beta secretion linked to inflammasome activation in MQ. Moreover, EgAgB outcompeted LPS for binding to DC/MQ and inhibited LPS-driven cytokine release more effectively than HDL. Binding assays and light scattering approaches confirmed EgAgB’s superior LPS-binding ability, supported by docking analysis showing a defined LPS-binding interface in EgAgB8/1 subunit. Regarding lipid handling, EgAgB acquired cholesterol from HDL and MQ, suggesting additional interactions with host cells that may have functional relevance and are currently under investigation. Our findings reveal novel activities for EgAgB: an extracellular LPS scavenger property that dampens TLR4- mediated inflammation in myeloid cells and a cholesterol uptake capacity from host lipoproteins/cells. Altogether, results support a dual role of EgAgB in E. granulosus biology, contacting host components to acquire essential lipids while contributing to parasite protection from host inflammation.