Altered Patterns of Gene Expression Underlying the Enhanced Immunogenicity of Radiation-Attenuated Schistosomes

Abstract

BackgroundSchistosome cercariae only elicit high levels of protective immunity against a challenge infection if they are optimally attenuated by exposure to ionising radiation that truncates their migration in the lungs. However, the underlying molecular mechanisms responsible for the altered phenotype of the irradiated parasite that primes for protection have yet to be identified.Methodology/Principal FindingsWe have used a custom microarray comprising probes derived from lung-stage parasites to compare patterns of gene expression in schistosomula derived from normal and irradiated cercariae. These were transformed in vitro and cultured for four, seven, and ten days to correspond in development to the priming parasites, before RNA extraction. At these late times after the radiation insult, transcript suppression was the principal feature of the irradiated larvae. Individual gene analysis revealed that only seven were significantly down-regulated in the irradiated versus normal larvae at the three time-points; notably, four of the protein products are present in the tegument or associated with its membranes, perhaps indicating a perturbed function. Grouping of transcripts using Gene Ontology (GO) and subsequent Gene Set Enrichment Analysis (GSEA) proved more informative in teasing out subtle differences. Deficiencies in signalling pathways involving G-protein–coupled receptors suggest the parasite is less able to sense its environment. Reduction of cytoskeleton transcripts could indicate compromised structure which, coupled with a paucity of neuroreceptor transcripts, may mean the parasite is also unable to respond correctly to external stimuli.Conclusions/SignificanceThe transcriptional differences observed are concordant with the known extended transit of attenuated parasites through skin-draining lymph nodes and the lungs: prolonged priming of the immune system by the parasite, rather than over-expression of novel antigens, could thus explain the efficacy of the irradiated vaccine.

Better Understanding of Anti-Schistosomal Strategies Through Microarray Analysis

“…changes and responses associated with this effective vaccination strategy have been highlighted as a useful research direction for the future [52]. The effects on gene expression that radiation attenuation has on the parasite itself have been the focus of a recent microarray study [53].…”

“…Dillon and colleagues used a focused S. mansoni microarray platform based primarily on sequences from "lung schistosomula" [25], to investigate the gene transcription in radiation attenuated parasites [53]. In vitro maintained mechanically derived schistosomula were subjected to microarray analysis and compared to controls that were not radiation attenuated.…”

Structure–function analysis of apical membrane‐associated molecules of the tegument of schistosome parasites of humans: prospects for identification of novel targets for parasite control

“…It was shown that infection of humans with live, RA parasites led to strong protection against subsequent challenge infections with normal cercariae (Correa-Oliveira et al, 2000;Ribeiro de Jesus et al, 2000). Vaccination of animal models with RA cercariae has thus led to an adult worm burden reduction in experimental schistosomiasis of 60-70% (Bickle et al, 1979a,b; CauladaBenedetti et al, 1991;Coulson et al, 1998;McManus, 1999;Dillon et al, 2008). The molecular mechanism of protection with RA is unclear; however, the immune response appears to result from transcriptional suppression in the attenuated parasites during the early stage of development (Dillon et al, 2008).…”

“…Vaccination of animal models with RA cercariae has thus led to an adult worm burden reduction in experimental schistosomiasis of 60-70% (Bickle et al, 1979a,b; CauladaBenedetti et al, 1991;Coulson et al, 1998;McManus, 1999;Dillon et al, 2008). The molecular mechanism of protection with RA is unclear; however, the immune response appears to result from transcriptional suppression in the attenuated parasites during the early stage of development (Dillon et al, 2008). Transcriptional suppression in RA was observed for a variety of genes including those encoding tegument proteins, members of signalling pathways associated with GPCRs, neurotransmitters and cytoskeletal components.…”

Molecular interactions of proteins associated with surface membrane biogenesis and renewal in the tegument of Schistosoma mansoni

“…Secondly, and more likely, the exposure of SmTSP-2 on the apical membrane may be a stage-specific phenomenon and a feature of the transition of the parasite from a free-living cercaria to the parasitic schistosomula stage. This transformation seems to be the phase that is vulnerable to immune attack by the host (Dillon et al, 2008; Chapter 3Characterisation of Schistosoma mansoni DLCs and TALs in the parasite life cycle …”