The planorbid snail Biomphalaria glabrata responded to exposure to either the compatible digenetic trematode
Echinostoma paraensei or the incompatible species Echinostoma trivolvis by producing increased amounts of several
distinctive plasma polypeptides. These polypeptides characteristically precipitated from plasma when mixed with
secreted–excreted products (SEP) of sporocysts or rediae from either digenean species. In contrast, control snails, or snails
that had been wounded or infected with bacteria (Serratia marcesens or Staphylococcus epidermidis) showed no obvious
plasma alterations and no precipitates formed when their plasma was mixed with SEP. Another planorbid species, Helisoma
trivolvis, which displays reverse compatibility for the echinostome species used, also responded to exposure to both
echinostomes by increased production of plasma polypeptides that precipitated in the presence of SEP. With some
individual variation, these 2 snail species synthesized 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 bound by these antibodies raising the possibility that they too contain fibrinogen domains. The
results are suggestive of a general ability of these 2 planorbid snails to detect the presence of echinostomes even if the latter
are subsequently incapable of development. The complex response they then mount, one not evoked by other challenges
such as wounding or bacterial infection, may represent a dedicated response to a frequently encountered group of
pathogenic parasites, the digeneans (echinostomes).
