Generation of a Novel Bacteriophage Library Displaying scFv Antibody Fragments from the Natural Buffalo Host to Identify Antigens from Adult Schistosoma japonicum for Diagnostic Development.

The development of effective diagnostic tools will be essential in the continuing fight to reduce schistosome infection; however, the diagnostic tests available to date are generally laborious and difficult to implement in current parasite control strategies. We generated a series of single-chain antibody Fv domain (scFv) phage display libraries from the portal lymph node of field exposed water buffaloes, Bubalus bubalis, 11-12 days post challenge with Schistosoma japonicum cercariae. The selected scFv-phages showed clear enrichment towards adult schistosomes and excretory-secretory (ES) proteins by immunofluorescence, ELISA and western blot analysis. The enriched libraries were used to probe a schistosome specific protein microarray resulting in the recognition of a number of proteins, five of which were specific to schistosomes, with RNA expression predominantly in the adult life-stage based on interrogation of schistosome expressed sequence tags (EST). As the libraries were enriched by panning against ES products, these antigens may be excreted or secreted into the host vasculature and hence may make good targets for a diagnostic assay. Further selection of the scFv library against infected mouse sera identified five soluble scFv clones that could selectively recognise soluble whole adult preparations (SWAP) relative to an irrelevant protein control (ovalbumin). Furthermore, two of the identified scFv clones also selectively recognised SWAP proteins when spiked into naïve mouse sera. These host B-cell derived scFvs that specifically bind to schistosome protein preparations will be valuable reagents for further development of a cost effective point-of-care diagnostic test.

Using the local immune response from the natural buffalo host to generate an antibody fragment library that binds the early larval stages of Schistosoma japonicum.

Antibodies isolated from the local draining inguinal lymph node of field exposed-water buffaloes following challenge with Schistosoma japonicum cercariae showed high reactivity towards S. japonicum antigen preparations and bound specifically to formaldehyde-fixed S. japonicum schistosomules. Using this specific local immune response we produced a series of single-chain antibody Fv domain libraries from the same lymph nodes. Removal of phage that cross reacted with epitopes on adult parasites yielded a single-chain antibody Fv domain-phage library that specifically bound to whole formaldehyde-fixed and live S. japonicum schistosomules. DNA sequencing indicated clear enrichment of the single-chain antibody Fv domain library for buffalo B-cell complementarity determining regions post-selection for schistosomule binding. This study also revealed that long heavy chain complementarity determining regions appear to be an important factor when selecting for antibody binding fragments against schistosomule proteins. The selected single-chain antibody Fv domain-phage were used to probe a schistosome-specific protein microarray, which resulted in the recognition of many proteins expressed across all schistosome life-cycle stages. Following absorption to adult worms, the single-chain antibody Fv domain-phage library showed significantly reduced binding to most proteins, whilst two proteins (NCBI GenBank accession numbers AY915878 and AY815196) showed increased binding. We have thus developed a unique set of host derived single-chain antibody Fv domains comprising buffalo B-cell variable regions that specifically bind to early S. japonicum life-stages.

Protein depletion using IgY from chickens immunised with human protein cocktails.

Given that proteomic analysis of complex protein mixtures may be restricted by the presence of highly abundant proteins, sample preparation to remove abundant proteins is essential for the analysis of low abundance proteins. Chickens are effective producers of antibodies (IgY) against mammalian proteins, able to produce large quantities of antibodies that can be recovered by simple non-intrusive extraction of egg yolk. The extraction procedure described uses a modification of the water dilution method (WD) to deplete lipids and lipoproteins followed by sequential precipitation with 31% ammonium sulphate and 12% poly ethylene glycol (PEG) producing IgY antibodies with greater than 95% purity and no loss in immunoreactivity. In the present study, various cocktails of the 12 most abundant human plasma proteins were used as immunogens to produce IgY antibodies. The anti-cocktail IgY antibodies were effectively used to sequentially and selectively immunodeplete abundant proteins from plasma. Also, affinity depletion (e.g., Affi-Gel Blue) was combined with immunodepletion to sequentially deplete abundant proteins from both plasma and urine. The current approach described allows the end user to mix and match sets of IgY cocktails to deplete tailored sets of targeted proteins dependent on their end use application.