Immunology of a unique biological structure: the Echinococcus laminated layer

The larval stages of the cestode parasites belonging to the genus Echinococcus grow within internal organs of humans and a range of animal species. The resulting diseases, collectively termed echinococcoses, include major neglected tropical diseases of humans and livestock. Echinococcus larvae are outwardly protected by the laminated layer (LL), an acellular structure that is unique to this genus. The LL is based on a fibrillar meshwork made up of mucins, which are decorated by galactose-rich O-glycans. In addition, in the species cluster termed E. granulosus sensu lato, the LL features nano-deposits of the calcium salt of myo-inositol hexakisphosphate (Insp(6)). The main purpose of our article is to update the immunobiology of the LL. Major recent advances in this area are (i) the demonstration of LL debris at the infection site and draining lymph nodes, (ii) the characterization of the decoy activity of calcium Insp(6) with respect to complement, (iii) the evidence that the LL mucin carbohydrates interact specifically with a lectin receptor expressed in Kupffer cells (Clec4F), and (iv) the characterization of what appear to be receptor-independent effects of LL particles on dendritic cells and macrophages. Much information is missing on the immunology of this intriguing structure: we discuss gaps in knowledge and propose possible avenues for research.

Automated summary

This article updates the immunobiology of the laminated layer (LL) in larval stages of cestode parasites belonging to the genus Echinococcus. The LL is a unique acellular structure, characterized by mucins decorated with galactose-rich O-glycans and nano-deposits of the calcium salt of myo-inositol hexakisphosphate (Insp(6)). Recent advances include the discovery of LL debris at infection sites and draining lymph nodes, the characterization of calcium Insp(6)'s decoy activity with respect to complement, the specific interaction of LL mucin carbohydrates with a lectin receptor expressed in Kupffer cells (Clec4F), and receptor-independent effects of LL particles on dendritic cells and macrophages. However, there is still much information missing on the immunology of LL, and further research is needed to fill these gaps.