Antigenic variation in 'Schistosoma'

Sealey, Katie Lynn (2011) Antigenic variation in 'Schistosoma'. (MSc(R) thesis), Kingston University, .


Schistosomes have an outer tegument that protects them from the host immune system. Parasite antigens expressed on or within the surface layer of the tegument have been suggested to be potential vaccine targets such as tetraspanin 23 (TSP23). Little is known about the evolution and diversity of tegumental antigens, an important consideration given that vaccines are being designed and are failing. Moreover, these antigens, including TSP23, are in direct contact with the host immune system, and so accelerated and adaptive evolution may be occurring. Species of 'Schistosoma' infect a variety of definitive hosts. The way in which these hosts are shaping the evolution of antigens across different species of 'Schistosoma' needs investigating. Much attention has been focussed on the production of an effective multi-species vaccine against the schistosomes, and there has been little success in absolute clearance or even establishment of continued immune memory post-infection. The aim of this study was therefore to investigate the evolution of schistosome antigens within and across parasite species to identify genetic changes that could alter the shape of the resultant antigenic proteins. This will also shed light on the speciation, divergence and adaptive evolution events among populations of schistosomes as a result of their definitive hosts. PCR and bioinformatic tools were used to analyse the antigenic and structural diversity of tegumental antigens. Results revealed antigenic and structural diversity in these antigens including TSP23 across species and within populations of 'Schistosoma', and suggest that the definitive host has played a part in positive and adaptive evolution of schistosomes. Furthermore, efficient tools have been developed to examine vaccine candidate antigens and their interactions with the host as a means of understanding the complications of vaccine design.

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