Echinococcus granulosus equinus: an ultrastructural study of the laminated layer, including changes on incubating cysts in various media

Abstract

The microfibrillate component of the laminated layer of Echinococcus granulosus equinus contains, except for the zone adjacent to the germinal layer, aggregates of electron-dense bodies displaying a sub-structure of electron-lucent spheres. The tegumentary syncytial cytoplasm contains randomly distributed electron-dense granules, many occurring near the apical plasmalemma, although exocytosis was rarely seen. Granules, similar in size and sub-structure to the bodies of the aggregates, also occur in the internuncial connexions and tegumentary cytons, suggesting that they may be produced in the cytons and released into the laminated layer via the internuncial connexions and tegumentary cytoplasm. Cysts incubated for 0.5-2.5 h in serum- and non-serum-containing media showed differences from non-incubated cysts. The distal half of the syncytium contained a progressive increase in the number of granules (distal: proximal 1.9:1 at 2.5 h; cf. 1:1 in non-incubated cysts), and exocytosis of granules into the laminated layer adjacent to the cyst had occurred. This cannot be attributed wholly to serum proteins. Cysts incubated for 21 h appeared 'normal', suggesting re-establishment of an equilibrium. Since the matrix of the laminated layer is considered homologous to the glycocalyx of other cestodes, the possible protective role played by the granules/bodies, characteristic of Echinococcus spp., is discussed.

Unique precipitation and exocytosis of a calcium salt of myo‐inositol hexakisphosphate in larval Echinococcus granulosus

“…3A) have indicated that if they exist, they are much less abundant than the IP 6 -Ca(II) salt. Richards et al [1983a] had described that granules apparently identical to the ones in the LL were present inside vesicles in the germinal layer cells. Our observation that a treatment removing IP 6 selectively from the HCW led to the disappearance of the granules present both in the LL and within cells confirms that the two are the same structure.…”

“…Electron micrographs of the E. granulosus HCW have consistently shown that the LL is formed by two ultrastructural elements: a predominant microfibrillar matrix and the granular bodies [Morseth, 1967;Bortoletti and Ferretti, 1978;Richards et al, 1983a;Rogan and Richards, 1989]. The microfibrillar matrix stains positive for carbohydrates, and is thus thought to be made up from the glycoconjugates that account for the bulk of the LL chemically [Richards et al, 1983a].…”

“…The microfibrillar matrix stains positive for carbohydrates, and is thus thought to be made up from the glycoconjugates that account for the bulk of the LL chemically [Richards et al, 1983a]. The granular element was described in detail by Richards et al [1983a]: it consists of naturally electron-dense bodies of defined size (41 AE 1 nm in diameter) that are found irregularly dispersed, individually or in aggregates, among the fibres. Individual granules are also observed within vesicles in germinal layer cells, and seem to be exocytosed towards the LL.…”

Biology and Systematics of Echinococcus

“…It is a carbohydrateeprotein complex of highly glycosylated mucin glycoproteins (Kilejian and Schwabe, 1971). Ultrastructurally it can be seen to be a microfibrillate, threedimensional meshwork matrix in which aggregates of electron-dense (Richards et al, 1983). The origin of the laminated layer was controversial for some time, but electron microscopy and in vitro studies have unequivocally demonstrated that it is entirely of parasite (germinal layer) origin (see Thompson, 1995).…”

Development of truncated microtriches inEchinococcus granulosus protoscolices

“…This differentiation of truncated microtriches is considered to be one step in the evolution of the protoscolex into a cyst because truncated microtriches are characteristic of the germinative membrane of both the hydatid cyst and the brood capsule wall. Furthermore, truncated microtriches seem to be linked to the formation of the laminated layer (Harris et al 1989;Casado et al 1992), which is an effective barrier against the host's immunological response (Richards et al 1983;Heath 1986).…”