PGE2 generation and release by the larval stage of the cestode, taenia taeniaeformis

The existence of an arachidonate cascade in invertebrate species has been little explored. We therefore sought to determine if two important prostanoid compounds, PGE2 and prostacyclin, PGI2 were generated and released by the larval stage of the cat tapeworm, Taenia taeniaeformis. PGE2 and PGI2 were identified by specific radioimmunoassay after thin layer chromatography of chloroform/methanol extracts of the worms or in vitro saline culture media. We detected a release of 176-182 pg of PGE2 from 2 worms after a 60' incubation at 37 degrees C with 4.5 mM exogenous sodium arachidonate. No release of PGI2 was detected immunochemically although 41 pg of immunoreactive material was identified in chloroform/methanol extracts of the worm alone. We therefore suggest that modulation of host immune responses could occur by the generation and release of prostanoid compounds such as PGE2, lipids which markedly suppress host cellular reactivity to the parasite. Secondly, the lack of any clot formation around the living organism may well reflect PGI2 presence at the surface of the parasite membrane. Although these findings are at present limited to larval cestodes we would propose that they may be more general means of evading host responses than heretofore suspected.