Abstract
Interactions between early developing Schistosoma mansoni larval stages and the hemolymph of its snail intermediate host represent the first molecular encounter with the snail’s immune system. To gain a more comprehensive understanding of this early parasite-host interaction, biotinylated sporocyst tegumental membrane (Mem) proteins and larval transformation proteins (LTP) were affixed to streptavidin-agarose beads and used as affinity matrices to enrich for larval-reactive plasma proteins from susceptible (NMRI) and resistant (BS-90) strains of the snail Biomphalaria glabrata. Nano-LC/MS-MS proteomic analyses of isolated plasma proteins revealed a diverse array of 94 immune-and nonimmune-related plasma proteins. Included among the immune-related subset were pattern recognition receptors (lectins, LPS-binding protein, thioester-containing proteins-TEPs), stress proteins (HSP60 and 70), adhesion proteins (dermatopontins), metalloproteases (A Disintegrin And Metalloproteinase (ADAM), ADAM-related Zn proteinases), cytotoxins (biomphalysin) and a Ca2+-binding protein (neo-calmodulin). Variable immunoglobulin and lectin domain (VIgL) gene family members, including fibrinogen-related proteins (FREPs), galectin-related proteins (GREPs) and C-type lectin-related proteins (CREPs), were the most prevalent of larval-reactive immune lectins present in plasma. FREPs were highly represented, although only a subset of FREP subfamilies (FREP 2, 3 and 12) were identified, suggesting potential selectivity in the repertoire of plasma lectins recognizing larval glycoconjugates. Other larval-binding FREP-like and CREP-like proteins possessing a C-terminal fibrinogen-related domain (FReD) or C-type lectin binding domain, respectively, and an Ig-fold domain also were identified as predicted proteins from the B. glabrata genome, although incomplete sequence data precluded their placement into specific FREP/CREP subfamilies. Similarly, a group of FReD-containing proteins (angiopoeitin-4, ficolin-2) that lacked N-terminal Ig-fold(s) were identified as a distinct group of FREP-like proteins, separate from the VIgL lectin family. Finally, differential appearance of GREPs in BS-90 plasma eluates, and others proteins exclusively found in eluates of the NMRI strain, suggested snail strain differences in the expression of select larval-reactive immune proteins. This hypothesis was supported by the finding that differential gene expression of the GREP in BS-90 and ADAM in NMRI snail strains generally correlated with their patterns of protein expression. In summary, this study is the first to provide a global comparative proteomic analysis of constitutively expressed plasma proteins from susceptible and resistant B. glabrata strains capable of binding early-expressed larval S. mansoni proteins. Identified proteins, especially those exhibiting differential expression, may play a role in determining immune compatibility in this snail host-parasite system. A complete listing of raw peptide data are available via ProteomeXchange using identifier PXD004942.
Highlights
Human blood flukes of the genus Schistosoma are the causative agents of schistosomiasis, and represent one of the most important of the neglected tropical diseases (WHO, http://www. who.int/mediacentre/factsheets/fs115/en/)
Expression of plasma lectin genes appears to be associated with larval resistance in B. glabrata, few studies have attempted an in depth analysis of geneencoded lectins, and other immune proteins, that are capable of directly binding schistosome larvae
Using affinity matrices linked to schistosome proteins expressed during early larval development, we identified and compared the parasite-reactive plasma proteins from the susceptible NMRI and resistant BS-90 strains of B. glabrata
Summary
Human blood flukes of the genus Schistosoma are the causative agents of schistosomiasis, and represent one of the most important of the neglected tropical diseases (WHO, http://www. who.int/mediacentre/factsheets/fs115/en/). For the blood fluke Schistosoma mansoni, miracidial penetration of, and successful development to the primary sporocyst within, its snail host Biomphalaria spp. is essential to the continued parasitic transmission to humans. Snail plasma-larval schistosome protein interactions early period of intramolluscan larval development and the host responses to parasite infection result in a myriad of cellular, biochemical and molecular interactions that are still poorly understood [4,5,6,7,8]. Upon entry into susceptible strains of Biomphalaria spp., S. mansoni miracidia undergo dramatic morphologic and physiologic changes associated with early larval development. During this miracidium- to-sporocyst transition, the parasite produces and presents a complex repertoire of molecules to the snail host’s immune system in the form of glycoconjugates at the tegumental surface. LTP have been shown to influence various immune-related hemocyte functions such as motility, phagocytosis, reactive oxygen species (ROS) production, and gene/protein expression [4,5,7] suggesting a possible role of specific LTP-hemolymph interactions in determining success or failure in establishing initial infections
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