Glycotope Sharing between Snail Hemolymph and Larval Schistosomes: Larval Transformation Products Alter Shared Glycan Patterns of Plasma Proteins Timothy P. Yoshino 1 *, Xiao-Jun Wu 1 , Hongdi Liu 1 , Laura A. Gonzalez 1 , Andre ´ M. Deelder 2 , Cornelis H. Hokke 2 1 Department of Pathobiological Sciences, University of Wisconsin School of Veterinary Medicine, Madison, Wisconsin, United States of America, 2 Department of Parasitology, Center for Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands Abstract Recent evidence supports the involvement of inducible, highly diverse lectin-like recognition molecules in snail hemocyte- mediated responses to larval Schistosoma mansoni. Because host lectins likely are involved in initial parasite recognition, we sought to identify specific carbohydrate structures (glycans) shared between larval S. mansoni and its host Biomphalaria glabrata to address possible mechanisms of immune avoidance through mimicry of elements associated with the host immunoreactivity. A panel of monoclonal antibodies (mABs) to specific S. mansoni glycans was used to identify the distribution and abundance of shared glycan epitopes (glycotopes) on plasma glycoproteins from B. glabrata strains that differ in their susceptibilities to infection by S. mansoni. In addition, a major aim of this study was to determine if larval transformation products (LTPs) could bind to plasma proteins, and thereby alter the glycotopes exposed on plasma proteins in a snail strain-specific fashion. Plasma fractions (,100 kDa/.100 kDa) from susceptible (NMRI) and resistant (BS-90) snail strains were subjected to SDS-PAGE and immunoblot analyses using mAB to LacdiNAc (LDN), fucosylated LDN variants, Lewis X and trimannosyl core glycans. Results confirmed a high degree of glycan sharing, with NMRI plasma exhibiting a greater distribution/abundance of LDN, F-LDN and F-LDN-F than BS-90 plasma (,100 kDa fraction). Pretreatment of blotted proteins with LTPs significantly altered the reactivity of specific mABs to shared glycotopes on blots, mainly through the binding of LTPs to plasma proteins resulting in either glycotope blocking or increased glycotope attachment to plasma. Many LTP-mediated changes in shared glycans were snail-strain specific, especially those in the ,100 kDa fraction for NMRI plasma proteins, and for BS-90, mainly those in the .100 kDa fraction. Our data suggest that differential binding of S. mansoni LTPs to plasma proteins of susceptible and resistant B. glabrata strains may significantly impact early anti-larval immune reactivity, and in turn, compatibility, in this parasite-host system. Citation: Yoshino TP, Wu X-J, Liu H, Gonzalez LA, Deelder AM, et al. (2012) Glycotope Sharing between Snail Hemolymph and Larval Schistosomes: Larval Transformation Products Alter Shared Glycan Patterns of Plasma Proteins. PLoS Negl Trop Dis 6(3): e1569. doi:10.1371/journal.pntd.0001569 Editor: Matty Knight, Biomedical Research Institute, United States of America Received October 21, 2011; Accepted February 4, 2012; Published March 20, 2012 Copyright: ß 2012 Yoshino et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by National Institutes of Health grant no. 2RO1AI015503 to TPY. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: yoshinot@svm.vetmed.wisc.edu Introduction Glycans are complex carbohydrate (CHO) chains normally covalently bound to polypeptides, lipids or other carrier molecules. Glycoconjugates such as glycoproteins, glycolipids and proteogly- cans represent one of the most prominent classes of molecules exhibited by schistosomes. Schistosome glycans are highly diverse structurally and have been implicated in a variety of physiological processes during schistosome infection of its mammalian host, most notably their involvement in modulating protective immune responses and immunopathology (see reviews [1–3]). Similarly glycans are also highly expressed in the free-swimming miracidial and intramolluscan developmental stages of Schistosoma spp. as shown by earlier exogenous lectin-binding studies [4,5], and more recent glycotope/glycomic analyses [6–9]. However, despite the presence of diverse glycans associated with the larval surface and its secretions/excretions, their functional significance remains unknown. A popular notion that recently has gained traction in the Biomphalaria glabrata-Schistosoma mansoni system poses that larval glycans and/or their associated glycoconjugates may be serving as pathogen-associated molecular patterns (PAMPs) that interact with lectin-like pathogen recognition receptors (PRRs), thereby medi- ating innate immune responses to invading miracidia (see reviews [10–13]). This concept has been incorporated into a proposed mechanism, termed compatibility polymorphism [14], in which it is hypothesized that high molecular diversity in relevant PAMP and PRR systems can provide the necessary variation in receptor- ligand interactions to account for differences in infection rates seen in different snail-schistosome strain combinations [15]. Two candidate gene families that fulfill the basic requirements of exhibiting high molecular polymorphism and potential functional diversity are the fibrinogen-related proteins or Freps, lectin-like proteins in plasma of B. glabrata snails [16] and a family of polymorphic mucins from S. mansoni (SmPoMuc; [17]). Recent studies have reported the selective ability of SmPoMuc to form complexes with Freps from snail plasma [18], as well as the demonstration of a direct linkage between expression of one B. glabrata Frep (Frep 3) and resistance to trematode infection [19], www.plosntds.org 1 March 2012 | Volume 6 | Issue 3 | e1569