A FAMILY OF FIBRINOGEN-RELATED PROTEINS THAT PRECIPITATES PARASITE-DERIVED MOLECULES IS PRODUCED BY AN INVERTEBRATE AFTER INFECTION

After infection with the digenetic trematode Echinostoma paraensei, he molymph of the snail Biomphalaria. glabrata contains lectins comprised of 65-kDa subunits that precipitate polypeptides secreted by E. parae nsei intramolluscan larvae, Comparable activity is lacking in hemolymp h of uninfected snails. Three different cDNAs with sequence similariti es to peptides derived from the 65-kDa lectins were obtained and unexp ectedly found to encode fibrinogen-related proteins (FREPs). These FRE Ps also contained regions with sequence similarity to Ig superfamily m embers, B. glabrata has at least five FREP genes, three of which are e xpressed at increased levels after infection, Elucidation of component s of the defense system of B. glabrata is relevant because this snail is an intermediate host for Schistosoma mansoni, the most widely distr ibuted causative agent of human schistosomiasis. These results are nov el in suggesting a role for invertebrate FREPs in recognition of paras ite-derived molecules and also provide a model for investigating the d iversity of molecules functioning in nonself-recognition in an inverte brate.