SCHISTOSOMA-MANSONI - EXCRETORY-SECRETORY POLYPEPTIDES EXHIBIT SELECTIVE BINDING TO PLASMA COMPONENTS OF THE SNAIL BIOMPHALARIA-GLABRATA

Previous studies have shown that Schistosoma mansoni excretory-secreto ry polypeptides (ESP) inhibit various internal defense functions of he mocytes from Biomphalaria glabrata and that plasma also may exert a mo dulatory effect on hemocyte activity, To better understand how plasma may influence hemocyte-schistosome interactions in inbred strains of s nails, biotinylated ESP (b-ESP) were used as probes to identify ESP-re active plasma components and partially characterize the nature of thei r binding interactions. In a plasma binding assay, b-ESP bound in a do se-dependent fashion to immobilized snail plasma, although no quantita tive differences in ESP reactivity to plasma of schistosome-susceptibl e (M-line) and resistant (13-16-R1) snail strains were detected. Moreo ver, co-incubation of b-ESP with homologous plasma or pretreatment of plasma with nonbiotinylated ESP in the plate assay significantly reduc ed b-ESP binding to immobilized plasma, indicating a specific interact ion between ESP and plasma. Pretreatment of b-ESP with mannose, porcin e stomach mucin, fetuin, and asialofetuin resulted in a significant in hibition of b-ESP binding to plasma, whereas pretreatment of immobiliz ed plasma with a cocktail of monosaccharides (including mannose), porc ine stomach mucin, and fetuin had no inhibitory effect. These data sug gest the presence of a carbohydrate-binding protein(s) in sporocyst ES P that is targeted to plasma glycoconjugates. Based on the carbohydrat e content of the major inhibitory glycoproteins, galactosyl and n-acet yl-galactosaminyl sugars may represent putative determinants for the l ectin-like ESP molecule(s). However, ESP binding to plasma from M-line and 13-16-R1 B. glabrata strains exhibited similar sugar and glycopro tein inhibition patterns. SDS-PAGE and electroblot analyses further de monstrated that ESP bound to a subset of separated plasma polypeptides , most prominently to a doublet of 52 and 54 kDa, and a complex of pro teins with molecular masses greater than 150 kDa. Other polypeptides e xhibiting weaker binding interactions included components of 34, 60, 6 4, 86, and 125 kDa. Although both M line and 13-16-R1 snail strains co ntained a similar complement of ESP-binding plasma proteins, ESP bindi ng to the 34- and 86-kDa proteins occurred at higher frequencies in su sceptible M-line plasma. It is concluded that ESP, released during in vitro transformation of S. mansoni miracidia, contain carbohydrate-rea ctive proteins capable of selectively binding to components of snail p lasma. Quantitative differences between snail strains in the occurrenc e of ESP-binding plasma molecules was documented. (C) 1995 Academic Pr ess, Inc.