Echinococcus granulosus antigen B modulates LPS-driven dendritic cell activation

Abstract

Antigen B (EgAgB) is the major lipoprotein produced by Echinococcus granulosus s.l. larvae. Its protein moiety is composed by EgAgB8/1-5 apolipoproteins, which belong to a cestode protein family capable of binding hydrophobic ligands. Its lipid moiety comprises several lipid classes, including triacylglycerides, fatty acids and phospholipids. Various reports suggested that EgAgB is involved in parasite immune regulation based on its ability to modulate LPS-induced activation of innate cells in vitro. We found that native EgAgB (immuno-purified from bovine hydatid cyst) and the recombinant EgAgB8/1 (expressed in insect cells) exhibited dose-dependent proinflammatory effects on bone marrow-derived dendritic cells (BMDC) but also a dose-dependent modulatory activity of LPS-induced cytokine response. Our hypothesis was that EgAgB could compete for TLR4 with LPS leading to a poor activation of this receptor. We explored the involvement of TLR4 in EgAgB-induced cytokine secretion using BMDC TLR4-KO. Results showed that EgAgB-induced IL6 secretion is dependent on TLR4. Furthermore, this receptor might also contribute to a potentiation effect on EgAgB-induced cytokine secretion in presence of Pam3CSK4. To analyze a direct interaction between EgAgB and TLR4, we assessed TLR4 dimerization, finding that LPS, but not EgAgB, induced TLR4 dimerization along 120 min stimulation. EgAgB was able to inhibit LPS-induced TLR4 dimerization and CD14 upregulation. In order to evaluate if EgAgB effect on BMDC would impact on T cell response, we assay mixed lymphocyte reaction finding that EgAgB stimulation of BMDC might contribute to increase IL4, IL5 meanwhile decrease TNFα secretion in presence of LPS. Overall, results suggest that EgAgB effects on BMDC are TLR4-dependent although might not be a consequence of direct interaction between EgAgB and TLR4. The EgAgB inhibitory effect on LPS-induced activation on BMDC could be promoted to generate a Th2 profile in presence of a TLR4 agonist.