Infection with Echinostoma paraensei (Digenea) Induces Parasite-Reactive Polypeptides in the Hemolymph of the Gastropod Host Biomphalaria glabrata

Abstract

In addition to affecting the endocrine systems and behavior of their hosts, parasites also have a profound impact on host internal defense systems. We have examined alterations in circulating plasma (cell-free hemolymph) polypeptides of the host snail Biomphalaria glabrata following exposure to the digenetic trematode parasites Echinostoma paraenseiand Schistosoma mansoni. Such humoral components are of interest because they may influence the outcome of host-parasite associations and they serve to illuminate the general nature of internal defense responses of invertebrates. Infection of juvenile B. glabrata with E. paraensei resulted in increased abundance of plasma polypeptides that precipitate parasite antigens present in excretory/secretory (E/S) products derived from cultured sporocysts of E. paraensei. When added to 70 {\textmu}l of plasma from snails infected for 4-14 days, 1 {\textmu}l of E/S products (``low dose'') precipitated a protein complex consisting of two previously described groups of polypeptides referred to as G1M and G2M. Addition of 10 {\textmu} of E/S products (``high dose'') to 70 {\textmu}l; of plasma from snails infected for 1-8 days precipitated a second complex comprised of covalently and noncovalently associated subunits of 65-70 kDa. The 65-70 kDa complex was also shown to bind to cilia from miracidia of E. paraensei. This complex serves as a marker for exposure to E. paraensei; it also precipitated from plasma of parasite-exposed snails that did not develop viable infections, such as refractory adults or juveniles exposed to noninfective aged miracidia. The G1M/G2M complex only precipitated from plasma of snails harboring viable E. paraensei infections. Plasma from unexposed snails or snails exposed to S. mansoni did not form precipitates upon exposure to E/S products, suggesting that production of these protein complexes is specifically provoked by E. paraensei.