title: Studies on resistance in snails. 3. Tissue reactions to Echinostoma lindoense sporocysts in sensitized and resensitized Biomphalaria glabrata.
abstract: The resistance of Biomphalaria glabrata snails that have been sensitized by various levels of irradiated or nonirradiated Echinostoma lindoense miracidia increased after a second challenge infection with nonirradiated miracidia of the same species. This was demonstrated by increased suppression of migrating capacity of invading sporocysts, an accelerated host tissue reaction, and a greater tendency of snail amebocytes to flatten while attacking the parasite. Three methods of elimination of invading sporocysts were observed: (1) encapsulation by amebocytes followed by destruction of the sporocysts; (2) expulsion of the sporocyst through the host epithelium after its encapsulation in the subepithelial tissues; (3) blockade of the parasite's entry into subepithelial tissues by a localized amebocyte aggregation. The basic mechanism of host snail response to a single or a repeated challenge infection appears to be similar, though an anamnestic reaction is evident in the accelerated response following a second challenge exposure.
mesh_terms: D000818:Animals; D001700:Biomphalaria / Q000276:immunology* / Q000469:parasitology; D004449:Echinostoma / Q000254:growth & development / Q000276:immunology*; D007111:Immunity, Cellular