Schistosoma mansoni host-exposed surface antigens characterized by sera and recombinant antibodies from schistosomiasis-resistant rats

Abstract

Antibodies from Schistosoma mansoni-infected rats, unlike mice, show a higher titer for schistosome apical tegumental antigens compared with non-apical membrane antigens. These antibodies bind to the surface of living lung stage worms and to formaldehyde-fixed adult worms. We produced a singlechain antibody Fv domain (scFv) phage library displaying the antibody repertoire of rats highly immune to schistosome infection and we selected for scFvs that recognize the host-exposed surface of worms. Five unique rat scFvs (Teg1, Teg4, Teg5, Teg20 and Teg37) were obtained which recognize schistosome surface epitopes. Each of the scFvs recognizes the surface of living schistosomula and lung stage schistosomules and/or the surface of formaldehyde-fixed adult worms. None of these scFvs reproducibly stained living adult worms. This suggests that a change occurs during the transition from lung schistosomules to 4 week adults such that at least some surface antigens, although remaining on the surface in living adult worms, can no longer be immunologically stained. Teg1 and Teg4 scFvs both recognize specific bands on Western blots. No bands were observed for the other three scFvs, suggesting that these scFvs may recognize non-protein or conformationally-dependent epitopes. Teg1 was unambiguously identified as recognizing the S. mansoni tetraspanin antigen, SmTSP-2, within the large extracellular domain. Teg4 recognizes a 35 kD band tentatively identified as Sm29 by proteomic analysis. These scFvs can now be used to characterize schistosome epitopes at the host-parasite interface, to target worms in vivo, and to study the mechanisms by which these worms naturally evade immune damage to the tegument within permissive hosts.

Efficacy and mechanism of action of arachidonic acid in the treatment of hamsters infected with Schistosoma mansoni or Schistosoma haematobium

“…Antischistosomal antibodies were also reported to bind to the surface of PZQ-treated worms [23]. It has been amply documented that host antibodies fail to bind to the surface membrane of intact healthy schistosomes in vivo [24] or in vitro [18,25]. In the study by Sepulveda et al [25], antibodies were able to bind to the surface of adult worms incubated in formaldehyde, which is able to permeate the outer lipid bilayer and cross-link proteins, leading to tegumental disorganisation that allows antibody access.…”

“…It has been amply documented that host antibodies fail to bind to the surface membrane of intact healthy schistosomes in vivo [24] or in vitro [18,25]. In the study by Sepulveda et al [25], antibodies were able to bind to the surface of adult worms incubated in formaldehyde, which is able to permeate the outer lipid bilayer and cross-link proteins, leading to tegumental disorganisation that allows antibody access. Extraction of adult worm surface membrane cholesterol with methyl-␤-cyclodextrin, and ARA-mediated NSMase activation and subsequent hydrolysis of surface membrane SM, reproducibly led to surface membrane exposure and specific antibody access [18].…”

Evaluation of the in Vivo Anti-Helminthic Activity, of Bridelia Micrantha, Chenopodium Ambrosoides and Ocimum Americanum Extracts Against Schistosoma Mansoni Infection in Mice.

“…This means the worms were mostly exposed to the treatment in the same location. Although it is not known which antigens, it is suggested that tegumental antigens of schistosomes vary as the worms mature from cercaria to schistosomule to adult which is thought to be a protective mechanism (Sepulveda et al 2010). This therefore suggests there are worm structural differences that may have led to the two extracts having more pronounced activity in either the 3 week or 4 week old worms.…”

Specific humoral response of hosts with variable schistosomiasis susceptibility

“…Knowledge of these antigens is not just important for the immunobiology of schistosomiasis but specifically could be exploited for the discovery and development of vaccines and diagnostics. The rat has long been used as a model of immunological resistance for both S. japonicum 7 , 8 , 18 , 59 and S. mansoni 10 , 11 , 15 , 60 infection. Consequently, we screened serum and tissue antibodies from the rat using a protein microarray.…”

“…Notably, immunity and infection severity vary considerably among these hosts allowing for comparison between susceptible and resistance traits. Of the laboratory animals, the mouse is fully permissive, passing viable schistosome eggs, whereas the rat ( Rattus norvegicus ) is semi‐permissive to both S. japonicum 7 , 8 and S. mansoni 9 , 10 , 11 infections. The resistant characteristics of the laboratory rat have been used for several decades in vaccine research 2 , 10 and resulted in the identification of the only schistosome vaccine antigen, Sh28GST, currently in phase III trials 4 , 12 , 13 .…”