Host-derived annexin II at the host–parasite interface of the Echinococcus granulosus hydatid cyst

Abstract

The hydatid cyst, caused by infection with the larval stages of Echinococcus granulosus, is bound by the two-layered hydatid cyst wall (HCW). The innermost (germinal) layer, which is the live parasite tissue, is responsible for the synthesis of the outer (laminated) layer, a massive extracellular structure that endows the cyst with mechanical resistance. Surprisingly, little is known about the composition of the HCW and of the laminated layer in particular, considering that it constitutes the host–parasite interface in hydatid disease. Ultrastructurally, the laminated layer is composed of irregularly arranged microfibrillar material in which irregular electron-dense bodies occur (reviewed in [1]). The major carbohydrate monomers in this structure are galactose and aminosugars (mostly galactosamine) [2–4]. The existence of structural proteins with disulphide bonds has been suggested [5], but no molecular species have been defined. The presence of the major diagnostic antigens (antigen 5 and antigen B) in the laminated layer is controversial (reviewed in [6]). In fact, the most abundant protein species in HCW extracts are host albumin and immunoglobulins [2,7]. This reflects the fact that the HCW is very permeable to host-derived macromolecules [8,9] and can bind certain of these [10]. Taken together, the available evidence allows us to envisage the laminated layer as a meshwork of parasite-derived carbohydrate and protein inside which both occluded and bound parasiteand host-derived macromolecules can occur. Here we show that one of the most abundant bound proteins in the HCW of bovine hydatids is the phospholipidand Ca-binding protein, annexin II, and that this protein derives from the host granulomatous inflammatory cells. Abbre6iations: HCW, hydatid cyst wall. * Corresponding author. Tel.: +59-82-4801196; fax: +5982-4874320. E-mail address: adiaz@bilbo.edu.uy (A. Diaz).