Echinococcus granulosus antigen B acts as an LPS-scavenging lipoprotein in vitro, preventing TLR4-mediated activation of dendritic cells

TL;DR

This study shows that a protein from Echinococcus granulosus can act as an LPS scavenger, reducing inflammation by blocking TLR4 activation in immune cells.

Contribution

The study reveals that EgAgB functions as an LPS-binding and -scavenging lipoprotein, offering a novel mechanism for its immunomodulatory effects.

Findings

EgAgB inhibits LPS-induced cytokine production and disrupts TLR4 dimerization and endocytosis in dendritic cells.

EgAgB binds LPS more effectively than human HDL, as shown by competitive binding assays and docking analysis.

The LPS scavenging activity of EgAgB is TLR4-independent but suppresses TLR4-mediated inflammatory responses.

Abstract

Echinococcus granulosus sensu lato antigen B (EgAgB) is a major parasite lipoprotein, produced by the hydatid and released at the host-parasite interface. Accumulating evidence supports that EgAgB may exert immunomodulatory effects on myeloid cells; however, the underlying molecular mechanisms remain poorly understood. We examined the impact of native EgAgB (nEgAgB) and recombinant EgAgB8/1 (rEgAgB) on lipopolysaccharide (LPS)-induced activation of bone marrow-derived dendritic cells (BMDC) to help elucidate these mechanisms. Both immunoaffinity-purified nEgAgB or rEgAgB induced modest BMDC activation, indicated by the production of IL-6, IL-12p40, and nitric oxide, but not IFN-β. This activation was primarily attributed to LPS traces in EgAgB preparations since it was nearly abolished by a specific TLR4 inhibitor and in Tlr4−/− BMDC, while EgAgB binding to BMDC was TLR4-independent. Notably, both nEgAgB and rEgAgB inhibited LPS-induced cytokine and nitric oxide production and disrupted TLR4 dimerization and endocytosis. Competitive binding assays showed that EgAgB and human high-density lipoprotein (hHDL) similarly inhibited LPS binding to macrophages and BMDC; however, EgAgB more effectively suppressed LPS-induced cytokine secretion. Contrastingly, EgAgB did not modulate BMDC responses to lipoteichoic acid, unlike hHDL. Using dynamic light scattering and an ELISA-like assay, we demonstrated a higher potential of EgAgB to bind LPS than hHDL. Additionally, docking analyzes suggest the presence of a defined LPS-binding interface in EgAgB8/1 subunit. Overall, these findings reveal a novel binding property of EgAgB, which enables it to act as an extracellular LPS scavenger, interfering with TLR4-mediated LPS recognition and downstream proinflammatory responses in myeloid cells.

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