Humoral response of the snail Biomphalaria glabrata to trematode infection: observations on a circulating hemagglutinin

The hemolymph of invertebrates often contains molecules that agglutinate vertebrate erythrocytes and that may function as humoral mediators of "non-self" recognition. The objectives of this study were to 1) determine if exposure of M line or 10-R2 strain Biomphalaria glabrata snails to infection with the trematodes Echinostoma paraensei and Schistosoma mansoni could increase agglutinating activity in snail hemolymph, and 2) identify particular hemolymph molecules with such activity. In some host-parasite combinations, such as juvenile M line snails and E. paraensei, infection provoked significant elevations in titer from as early as 2 days postinfection (dpi) through 15 dpi. In other combinations, as with 10-R2 snails and E. paraensei or S. mansoni, host responses were comparatively modest, yet still measurable. In general, E. paraensei and S. mansoni elicited different responses from the same host strain, and M line and 10-R2 snails responded differently to the same parasite. Further study of the response of juvenile M line snails to E. paraensei indicated that hemolymph agglutinating activity could be inhibited by several monosaccharides (including L-fucose) and by EDTA and EGTA. An affinity column containing L-fucose agarose beads was used to purify molecules with agglutinating activity from the hemolymph of such snails. The fraction eluted from the column by 0.2 M L-fucose was shown by SDS-PAGE to contain a broad band of 80-120 kD and, less consistently, a 200 kD band. Following extensive dialysis to remove L-fucose, this fraction had agglutinating activity. As a previous study has shown that the hemolymph of E. paraensei-infected snails contains significantly increased quantities of 80-120 kD polypeptides, it is concluded that polypeptides in this size range are responsible, at least in part, for the increased hemolymph agglutination activity in such snails.