Specificity of natural resistance to trematode infections in Biomphalaria glabrata

The 10-R2 strain of Biomphalaria glabrata was strongly resistant to various strains of Schistosoma mansoni in its laboratory of origin (NIH) and to three strains of S. mansoni we tested against it. However, subsequent development of three inbred lines of B. glabrata 10-R2 snails, separately maintained in our San Francisco laboratory, showed slight loss of resistance in one colony, very much less resistance (or partial susceptibility) in another, and retention of the original resistance in a third to the Puerto Rico (PR-1) strain of S. mansoni. No selection for resistance to infection was involved in the breeding protocol for these 10-R2 lines, so the changes were apparently random ones that became established in the separate inbred substrains. In spite of their changed response to the PR-1 strain of S. mansoni, all three 10-R2 substrains retained only slightly diminished resistance to S. mansoni Lc-1 strain and an essentially undiminished resistance to irradiated Echinostoma lindoense, E. paraensei and E. liei sporocysts. This suggests that natural resistance to S. mansoni PR-1 in B. glabrata is specific, a response that differs from the host response to either S. mansoni Lc-1 or to the echinostomes.