Tandem repeat recombinant proteins as potential antigens for the sero-diagnosis of Schistosoma mansoni infection

Dynamics of serological responses to defined recombinant proteins during Schistosoma mansoni infection in mice before and after the treatment with praziquantel

To eliminate schistosomiasis, appropriate diagnostic tests are required to monitor its prevalence and transmission, especially in the settings with low endemicity resulting from the consecutive mass drug administration. Antibodies that react with either crude soluble schistosome egg antigens or soluble worm antigen preparations have been used to monitor infection in low-prevalence regions. However, these detection methods cannot discriminate current and past infections and are cross-reactive with other parasites because both antigens contain numerous proteins and glycans from schistosomes, and standard preparations need maintenance of the life cycle of the schistosome. To evaluate the potential utility of nine recombinant Schistosoma mansoni proteins as single defined antigens for serological diagnosis, we monitored the kinetics of antibodies to each antigen during S. mansoni infection in mice before and after the treatment with praziquantel. C57BL/6 mice were infected with 50 cercariae. The levels of immunoglobulin G (IgG) raised against five recombinant antigens (RP26, sm31, sm32, GST, and LAP1) significantly increased as early as 2-4 weeks after infection and rapidly declined by 2 weeks after the treatment, whereas those raised against crude S. mansoni egg antigens or other antigens remained elevated long after the treatment. The IgG1 raised against RP26, sm31, and serpin decreased after the treatment with praziquantel, whereas the IgE raised against serpin declined strikingly after the treatment. This study clarifies the dynamics of the serological responses to recombinant S. mansoni proteins during infection and after the treatment with praziquantel and identifies several candidate antigens with potential utility in the monitoring and surveillance of schistosomiasis toward the elimination of schistosomiasis.

Transcriptome of the parasitic flatworm Schistosoma mansoni during intra-mammalian development

Schistosomes are parasitic blood flukes that survive for many years within the mammalian host vasculature. How the parasites establish a chronic infection in the hostile bloodstream environment, whilst evading the host immune response is poorly understood. The parasite develops morphologically and grows as it migrates to its preferred vascular niche, avoiding or repairing damage from the host immune system. In this study, we investigated temporal changes in gene expression during the intra-mammalian development of Schistosoma mansoni. RNA-seq data were analysed from parasites developing in the lung through to egg-laying mature adult worms, providing a comprehensive picture of in vivo intra-mammalian development. Remarkably, genes involved in signalling pathways, developmental control, and adaptation to oxidative stress were up-regulated in the lung stage. The data also suggested a potential role in immune evasion for a previously uncharacterised gene. This study not only provides a large and comprehensive data resource for the research community, but also reveals new directions for further characterising host-parasite interactions that could ultimately lead to new control strategies for this neglected tropical disease pathogen.

A perspective for improving the sensitivity of detection: The application of multi-epitope recombinant antigen in serological analysis of buffalo schistosomiasis

The sensitivity and specificity are two crucial aspects of addressing the efficacy of diagnostic antigens. Achilles' heel of low sensitivity rate exists in current diagnostic recombinant antigens for schistosomiasis detection. This study focused on the diagnosis of water buffalo schistosomiasis japonica and a perspective of improving recombinant antigens' sensitivity was assessed using archived 220 water buffalo sera (114 positive sera, 92 negative sera and 14 Paramphistomum-infected sera) and the method of enzyme-linked immunosorbent assay (ELISA). The subjects included two trivalent recombinant proteins, one bivalent antigen and two single-molecular antigens. The crude antigen SEA (soluble egg antigen) was employed as reference antigen. The highest sensitivity rate in the five recombinant antigens assigned to the trivalent multi-epitope antigen PA4 (95.61%, 109/114), no significant difference with SEA (100%, 114/114, p = .836), and showing remarkable differences with the two single-molecular antigens (p < 0.01). In term of specificity, two trivalent multi-epitope antigens PA4 (97.83%, 90/92), PA5 (100%, 92/92) and the bivalent antigen PA3 (98.91%, 91/92) had few differences with one monovalent antigens PA1 (97.83%, 90/92, p = .304/0.103/0.640), significant differences with another monovalent antigens PA2 (92.39%, 85/92, p < 0.01) and SEA (82.61%, 76/92, p < 0.01). Additional, all the recombinant antigens had low cross-reactivity (7.14%, 1/14, 0% for PA5) with serum samples of paramphistomiasis, contrast with that of SEA (50%, 7/14, p < 0.01). The results indicated that multi-epitope antigens have the possibility to improve diagnostic sensitivity and the trivalent multi-epitope antigen PA4 possesses greater likelihood to be a diagnostic antigen for water buffalo schistosomiasis.

Modulation of immune responses by Plasmodium falciparum infection in asymptomatic children living in the endemic region of Mbita, western Kenya

Individuals living in malaria endemic areas become clinically immune after multiple re-infections over time and remain infected without apparent symptoms. However, it is unclear why a long period is required to gain clinical immunity to malaria, and how such immunity is maintained. Although malaria infection is reported to induce inhibition of immune responses, studies on asymptomatic individuals living in endemic regions of malaria are relatively scarce. We conducted a cross-sectional study of immune responses in asymptomatic school children aged 4-16years living in an area where Plasmodium falciparum and Schistosoma mansoni infections are co-endemic in Kenya. Peripheral blood mononuclear cells were subjected to flow cytometric analysis and cultured to determine proliferative responses and cytokine production. The proportions of cellular subsets in children positive for P. falciparum infection at the level of microscopy were comparable to the negative children, except for a reduction in central memory-phenotype CD8⁺ T cells and natural killer cells. In functional studies, the production of cytokines by peripheral blood mononuclear cells in response to P. falciparum crude antigens exhibited strong heterogeneity among children. In addition, production of IL-2 in response to anti-CD3 and anti-CD28 monoclonal antibodies was significantly reduced in P. falciparum-positive children as compared to -negative children, suggesting a state of unresponsiveness. These data suggest that the quality of T cell immune responses is heterogeneous among asymptomatic children living in the endemic region of P. falciparum, and that the responses are generally suppressed by active infection with Plasmodium parasites.

Selecting targets for the diagnosis of Schistosoma mansoni infection: An integrative approach using multi-omic and immunoinformatics data

In order to effectively control and monitor schistosomiasis, new diagnostic methods are essential. Taking advantage of computational approaches provided by immunoinformatics and considering the availability of Schistosoma mansoni predicted proteome information, candidate antigens of schistosomiasis were selected and used in immunodiagnosis tests based on Enzime-linked Immunosorbent Assay (ELISA). The computational selection strategy was based on signal peptide prediction; low similarity to human proteins; B- and T-cell epitope prediction; location and expression in different parasite life stages within definitive host. Results of the above-mentioned analysis were parsed to extract meaningful biological information and loaded into a relational database developed to integrate them. In the end, seven proteins were selected and one B-cell linear epitope from each one of them was selected using B-cell epitope score and the presence of intrinsically disordered regions (IDRs). These predicted epitopes generated synthetic peptides that were used in ELISA assays to validate the rational strategy of in silico selection. ELISA was performed using sera from residents of areas of low endemicity for S. mansoni infection and also from healthy donors (HD), not living in an endemic area for schistosomiasis. Discrimination of negative (NEG) and positive (INF) individuals from endemic areas was performed using parasitological and molecular methods. All infected individuals were treated with praziquantel, and serum samples were obtained from them 30 and 180 days post-treatment (30DPT and 180DPT). Results revealed higher IgG levels in INF group than in HD and NEG groups when peptides 1, 3, 4, 5 and 7 were used. Moreover, using peptide 5, ELISA achieved the best performance, since it could discriminate between individuals living in an endemic area that were actively infected from those that were not (NEG, 30DPT, 180DPT groups). Our experimental results also indicate that the computational prediction approach developed is feasible for identifying promising candidates for the diagnosis of schistosomiasis and other diseases.

Serological approaches for the diagnosis of schistosomiasis - A review

Schistosomiasis is a common disease in endemic areas of Sub-Saharan Africa, South America and Asia. It is rare in Europe, mainly imported from endemic countries due to travelling or human migration. Available methods for the diagnosis of schistosomiasis comprise microscopic, molecular and serological approaches, with the latter detecting antigens or antibodies associated with Schistosoma spp. infection. The serological approach is a valuable screening tool in low-endemicity settings and for travel medicine, though the interpretation of any diagnostic results requires knowledge of test characteristics and a patient's history. Specific antibody detection by most currently used assays is only possible in a relatively late stage of infection and does not allow for the differentiation of acute from previous infections for therapeutic control or the discrimination between persisting infection and re-infection. Throughout the last decades, new target antigens have been identified, and assays with improved performance and suitability for use in the field have been developed. For numerous assays, large-scale studies are still required to reliably characterise assay characteristics alone and in association with other available methods for the diagnosis of schistosomiasis. Apart from S. mansoni, S. haematobium and S. japonicum, for which most available tests were developed, other species of Schistosoma that occur less frequently need to be taken into account. This narrative review describes and critically discusses the results of published studies on the evaluation of serological assays that detect antibodies against different Schistosoma species of humans. It provides insights into the diagnostic performance and an overview of available assays and their suitability for large-scale use or individual diagnosis, and thus sets the scene for serological diagnosis of schistosomiasis and the interpretation of results.