Defining the breadth of the host antibody repertoire during parasitic infection

During infection, the immune system generates antibodies that bind pathogen molecules to try and limit damage to the host. However, not all antibodies have the same function and some will have better neutralising efficiency. Developing methodologies to define the breadth of the host antibody repertoire against selected parasite antigens and which antibodies are the most efficient at hampering the function of these proteins could reveal new therapeutic approaches. Our research focuses on schistosomes, parasitic worms that reside in the blood vessels of their human hosts and infect over 200 million individuals every year, mostly in low- and middle-income countries. No vaccine is currently available but studies in populations from endemic areas and in animal models of schistosomiasis suggest that it is possible to develop some resistance to re-infection mediated, in part, by protective antibodies directed against an immature form of the parasite, the schistosomule. Because of their easier accessibility to host antibodies, proteins secreted by or displayed on the surface of the parasite are the most likely targets of protective antibodies. Using sera from mice with experimentally-induced resistance to re-infection and a collection of over 150 recombinant Schistosoma mansoni extracellular proteins (most of which are expressed by schistosomules), we have identified antibody responses to a subset of parasite proteins. Reactivity to these proteins was generally increased and a different balance of antibody isotypes was observed in protected sera compared to sera from animals with lower protection. The aim of the research project is to further characterise the molecular repertoire of these potentially protective antigen-specific antibodies by developing a methodology to isolate antigen-specific B cells. The proposed research project will involve the production of a small set of recombinant biotinylated parasite proteins in mammalian cells; these proteins will be oligomerised and fluorescently tagged, and used to identify antigen-specific B cells in murine models of schistosomiasis with different levels of protection. For each candidate antigen, reactive B-cells will be isolated by flow cytometry and sequenced to define the B-cell receptor repertoire to this antigen and the breadth of antibody produced during schistosomiasis infection.