Authors

T A Gasan¹; S Wilson²; J M Wawrzyniak²; E Tukahebwa³; K Hoffmann¹; I W Chalmers¹;  ¹ IBERS, Aberystwyth University, UK;  ² University of Cambridge, UK;  ³ Vector Control Division, Ministry of Health, Republic of Uganda, Uganda

Discussion

As an integral component of cellular communication, Extracellular Vesicles (EVs) have been described in both protozoa and metazoan parasites. Both larval schistosomula and mature adult Schistosoma mansoni worms release pre-packaged EVs, but to what end? Identifying and characterising proteins within schistosome EVs will aid in discernring their function(s) and may help develop potential schistosomiasis control strategies. To this end, this project aims to characterise the most abundant EV protein in the tissue-migrating schistosomula stage - Schistosoma mansoni Larval Extracellular Vesicle protein (SmLEV1).
Comparative sequence analysis demonstrates that while SmLEV1 has orthologs in all published Schistosoma genomes, it lacks any homologs outside of the genus, nor has any characterised protein domains. By employing qRT-PCR, we discovered differential expression of SmLEV1 across the schistosome lifecycle, with peak expression in cercariae as well as male biased expression in sexually reproductive adults. Importantly, SmLEV1 exhibits developmentally regulated alternative splicing during infection of the mammalian host. Specifically cercariae displayed a significantly different population of isoforms, with over twice the level of exon-5 expression, when compared with adult worms, but only two-thirds the expression of exon-8.
Recombinant expression of SmLEV1.3, the most abundant isoform in cercariae, has enabled investigation of the host's response to SmLEV1, in both the mouse model and endemic human populations. Interestingly, preliminary serological analysis from S. mansoni infected individuals shows a strong IgG1 response against SmLEV1 with minimal antigen-specific IgG4 and IgE measured; this finding is congruent to antibody responses generated against other surface/secreted schistosome proteins (e.g. SmLy6A, D, and SmTSP-2).
Collectively, these results point to SmLEV1 being an abundant, novel schistosome-specific, secreted protein (within EVs). Finally a murine model vaccination trial has been conducted to investigate the potential protective capabilities of an SmLEV1 vaccine.