Oncosphere immune responses

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... 

Table 15.2. Recombinant oncosphere antigens of taeniid cestodes, which have been shown to induce host-protective immune responses. ...

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. 

Fig. 11.7. Pattern of immune responses of an oncosphere of a taeniid cestode (e.g. Echinococcus granulosus) during initial penetration of the hatched oncosphere (initiating early immunity ) and its subsequent migration to, and establishment in, its definitive site, where it is subject to late immunity . The exact site of hatching (in man) is unknown most eggs probably hatch in the upper duodenum.

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). 

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