Schistosoma mansoni: a comparison of secreted vs nonsecreted eicosanoids in developing schistosomulae and adults.

We have determined that developing schistosomulae and adults of Schistosoma mansoni synthesize a wide range of eicosanoids when stimulated with linoleic acid, an essential fatty acid. Developing schistosomulae secrete 64%, while adults secrete over 80% of synthesized eicosanoids. On a per milligram soluble protein basis, eicosanoid secretion is ordered as follows: adult females greater than adult males much much greater than developing schistosomulae. Together one mature adult worm pair secreted approximately 4.36 micrograms prostaglandin E, 3.41 micrograms leukotriene B4, and 15.13 micrograms 5-hydroxyeicosatetraenoic acid (HETE) as determined by radioimmunoassay (RIA). High-performance liquid chromatography (HPLC) results have determined that 15-HETE is the major HETE species secreted by adults and developing schistosomulae. The immunosuppressant roles of 15-HETE, PGE, and LTB4 are discussed in relation to a possible mechanism for S. mansoni to evade the host immune system. Adults and schistosomules of S. mansoni have evolved rather sophisticated mechanisms for evading the host immune response. These include both host antigen acquisition and antigen shedding. In addition, young schistosomes have an as yet unidentified intrinsic defense mechanism against the host immune system. We postulate that part of the defense mechanism in schistosomules and adults may involve secretion of immunosuppressant eicosanoid species.