Comparative ORESTES-sampling of transcriptomes of immune-challenged Biomphalaria glabrata snails

The snail Biomphalaria glabrata (Gastropoda, Mollusca) is an important intermediate host for the human parasite Schistosoma mansoni (Digenea, Trematoda). Anti-pathogen responses of B. glabrata were studied towards a better understanding of snail immunity and host–parasite compatibility. Open reading frame ESTs (ORESTES) were sampled from different transcriptomes of M line strain B. glabrata, 12 h post-challenge with Escherichia coli (Gram-negative), Micrococcus luteus (Gram-positive) bacteria or compatible S. mansoni, and controls. The resulting 3123 ORESTES represented 2129 unique sequences (373 clusters, 1756 singletons). Of these, 175 (8.1%) were putative defense factors, including lectins, antimicrobial peptides and components of various immune-effector systems. Comparison of biological processes (GO-terms) within different transcriptomes indicated that B. glabrata increased oxygen transport and metal binding in reaction to all challenges. Comprehensive comparisons of transcriptomes revealed that responses of B. glabrata against bacteria were similar to each other and differed from the ineffective response to S. mansoni. Furthermore, the response to S. mansoni infection was less comprehensive than that to bacteria. Many novel (unknown) sequences were recovered in association with particular challenges. B. glabrata possesses multi-faceted, potent immune defenses. This agrees with the notion that S. mansoni is capable of immune-evasion and prevents effective host defense responses in order to survive in B. glabrata. Future analysis of the numerous unknown sequences recovered from challenged snails may reveal novel immune factors and provide increased understanding of immunity of B. glabrata in relation to parasite–host compatibility.