Evidence from two planorbid snails of a complex and dedicated response to digenean (echinostome) infection

The planorbid snail Biomphalaria glabrata responded to exposure to either t he compatible digenetic trematode Echinostoma pamensei or the incompatible species Echinostoma trivolvis by producing increased amounts of several dis tinctive plasma polypeptides. These polypeptides characteristically precipi tated from plasma when mixed with secreted-excreted products (SEP) of sporo cysts or rediae from either digenean species. In contrast, control snails, or snails that had been wounded or infected with bacteria (Serratia marcese ns or Staphylococcus epidermidis) showed no obvious plasma alterations and no precipitates formed when their plasma was mixed with SEP. Another planor bid species, Helisoma trivolvis, which displays reverse compatibility for t he echinostome species used, also responded to exposure to both echinostome s by increased production of plasma polypeptides that precipitated in the p resence of SEP. With some individual variation, these 2 snail species synth esized SEP-reactive plasma polypeptides forming diffuse bands centred at 53 , 65, 80-120 and 200 kDa (the latter absent in Helisoma trivolvis). The 53 kDa polypeptides had not been observed before, whereas the others have been noted from B. glabrata. The diffuse 65 kDa band was strongly bound by anti fibrinogen antibodies, supportive of earlier studies indicating it contains fibrinogen-related domains. The other specified polypeptides were also bou nd by these antibodies raising the possibility that they too contain fibrin ogen domains. The results are suggestive of a general ability of these 2 pl anorbid snails to detect the presence of echinostomes even if the latter ar e subsequently incapable of development. The complex response they then mou nt, one not evoked by other challenges such as wounding or bacterial infect ion, may represent a dedicated response to a frequently encountered group o f pathogenic parasites, the digeneans (echinostomes).