Oncosphere developing

Rajasekariah, G.R., Rickard, M.D. and Mitchell, G.F. (1980) Immunization of mice against infection with Taenia taeniaeformis using various antigens prepared from eggs, oncospheres, developing larvae and strobilocerci. International Journal for Parasitology 10, 315-324. 

Attention has already been drawn to the fact that immunity in the H. nana/rodent system represents an unique situation in that the oncosphere develops in a villus after penetration, so that the penetration and final encystment sites are essentially the same. Passive protection against H. nana in mice can be induced by serum transfer, not only prior to the oncospheral invasion, but also after invasion has taken place. Oncospheral agglutination has also been shown to occur in H. nana-infected mouse serum but never in uninfected sera (555). 

Oncospheres of many cestode species penetrate and develop into metacestodes within cysts (cysticerci, hydatid, multilocular) in the soft tissues of their rodent, ruminant or human hosts. Thus, species such as Echinococcus granulosus, E. multilocularis, Eaenia multiceps, T. ovis, E. saginata and E solium are of economic and medical importance. Such soft tissue invasion elicits a host immune response to resist the helminths. However, although some cysts may be destroyed as evidenced by involution or calcification, the host response is often too little - too late to eliminate the invaders. The susceptibility of the host to invasion is often due to successful evasive strategies... 

The discovery that oncosphere extracts provided a source of potent, protective antigens for both Taenia species and E. granulosus raised the potential for development of practical vaccines to prevent infections with economic and... 

Fig. 7.4. Embryonic development in the Cyclophyllidea (a) fertilised ovum (b) cleaving embryo (c) early preoncosphere (d) late preoncosphere (e) oncosphere. (After Rybicka, 1966.)...

The process of hatching in the Cyclophyllidea, which results in the release of the oncosphere, has been discussed in Chapter 7. The basic structure of a mature oncosphere (Fig. 8.16), which will not be discussed in detail here, does not vary substantially between species. It is composed essentially of (a) a thin covering epithelium with cytoplasmic extensions, (b) an additional complex system of muscles operating the three pairs of hooks, (c) a pair of large penetration glands, (d) a small core of germinative cells from which the next larval stage develops and (e) a primitive nervous system. 

Rather surprisingly, it was found (16), that the presence of glucose in the maintenance saline had no effect on survival (Figs. 8.19), which suggests that (like some trematode cercariae) the larvae are non-feeding during the hexacanth penetration phase. It is possible that the appropriate systems for active transport or diffusion do not develop until after penetration. Since so little is known regarding the metabolism of the oncosphere (see Chapter 7) it is not profitable to speculate further on this question without more experimental data. 

The immunobiology of this parasite is complicated by the fact that hosts can be infected (a) directly, via egg infections, or (b) indirectly, via cysticercoids (in beetles). In the direct life cycle, eggs hatch in the duodenum and oncospheres immediately penetrate the villi and develop into cysticercoids (Fig. 11.6). When fully developed, these break out of the villi, attach and... 

That the tissue phase of H. nana is highly immunogenic is witnessed by the fact that even a single oncosphere invading a villus can elicit complete protection (353). Moreover, this protection can develop within a few days. It must be stressed, however, that - as with most helminth parasites - the immune responses may vary substantially in different strains of the same host, a factor not always appreciated in these experiments. Immune responses known to be influenced by host genotype are listed in Table 11.3. 

Egg-induced immunity appears to involve stage-specific immunogens against (a) the tissue phase of egg challenge (early response) and (b) the lumen phase of cysticercoid challenge (late response). This immunogenetic pattern is thus similar to the development of early and late immunity in larval taeniid cestodes (Fig. 11.7). The effector mechanism of the early response has been shown to be thymus dependent, X-irradiation sensitive, cell mediated and antibody mediated the response is visualised by eosinophilia infiltration around the invading oncospheres (Fig. 11.6) (353). 

It is beyond the scope of this text to consider the immunodiagnosis of adult and larval cestode infections. Various aspects of this topic have been extensively reviewed by Flisser et al. (226), Fox et al. (228), Draper Lillywhite (183), Houba (337), Gottstein et al. (261), Rickard Lightowlers (690) and Walls Schantz (928). A major breakthrough in diagnosis has been the development of an anti-oncospheral monoclonal antibody for the unequivocal identification of eggs of Echinococcus spp. by immunofluorescence (154). 

Guttowa, A. (1958). Further research on the effect of temperature on the development of the cestode Triaenophorus lucii (Mull) embryos in eggs, and on the invadability of their oncospheres. Acta Parasitologica Polonica, 6 367—81. 

Heath, D. D. Lawrence, S. B. (1976). Echinococcus granulosus development in vitro from oncosphere to immature hydatid cyst. Parasitology, 73 417-23. 

Voge, M. Green, J. (1975). Axenic growth of oncospheres of Hymenolepis citelli(Cestoda) to fully developed cysticercoids. Journal of Parasitology, 61 291-7. 

Voge, M. Seidel, J. S. (1968). Continuous growth in vitro of Mesocestoides (Cestoda) from oncosphere to fully developed tetrathyridium. Journal of Parasitology, 54 269-71. 

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