Schistosoma mansoni venom allergen-like proteins: phylogenetic relationships, stage-specific transcription and tissue localization as predictors of immunological cross-reactivity

Human schistosomiasis in Nigeria: present status, diagnosis, chemotherapy, and herbal medicines

Schistosomiasis is a neglected tropical disease caused by a parasitic, trematode blood fluke of the genus Schistosoma. With 20 million people infected, mostly due to Schistosoma haematobium, Nigeria has the highest burden of schistosomiasis in the world. We review the status of human schistosomiasis in Nigeria regarding its distribution, prevalence, diagnosis, prevention, orthodox and traditional treatments, as well as snail control strategies. Of the country's 36 states, the highest disease prevalence is found in Lagos State, but at a geo-political zonal level, the northwest is the most endemic. The predominantly used diagnostic techniques are based on microscopy. Other methods such as antibody-based serological assays and DNA detection methods are rarely employed. Possible biomarkers of disease have been identified in fecal and blood samples from patients. With respect to preventive chemotherapy, mass drug administration with praziquantel as well as individual studies with artemisinin or albendazole have been reported in 11 out of the 36 states with cure rates between 51.1 and 100%. Also, Nigerian medicinal plants have been traditionally used as anti-schistosomal agents or molluscicides, of which Tetrapleura tetraptera (Oshosho, aridan, Aidan fruit), Carica papaya (Gwanda, Ìbẹ́pẹ, Pawpaw), Borreria verticillata (Karya garma, Irawo-ile, African borreria), and Calliandra portoricensis (Tude, Oga, corpse awakener) are most common in the scientific literature. We conclude that the high endemicity of the disease in Nigeria is associated with the limited application of various diagnostic tools and preventive chemotherapy efforts as well as poor knowledge, attitudes, and practices (KAP). Nonetheless, the country could serve as a scientific base in the discovery of biomarkers, as well as novel plant-derived schistosomicides and molluscicides.

Protective human IgE responses are promoted by comparable life-cycle dependent Tegument Allergen-Like expression in Schistosoma haematobium and Schistosoma mansoni infection

Schistosoma haematobium is the most prevalent of the human-infecting schistosome species, causing significant morbidity in endemically exposed populations. Despite this, it has been relatively understudied compared to its fellow species, S. mansoni. Here we provide the first comprehensive characterization of the S. haematobium Tegument Allergen-Like protein family, a key protein family directly linked to protective immunity in S. mansoni infection. Comparable with observations for S. mansoni, parasite phylogenetic analysis and relative gene expression combined with host serological analysis support a cross-reactive relationship between S. haematobium TAL proteins, exposed to the host immune system as adult worms die, and closely related proteins, exposed during penetration by the infecting cercarial and early schistosomulae stages. Specifically, our results strengthen the evidence for host immunity driven by cross-reactivity between family members TAL3 and TAL5, establishing it for the first time for S. haematobium infection. Furthermore, we build upon this relationship to include the involvement of an additional member of the TAL protein family, TAL11 for both schistosome species. Finally, we show a close association between experience of infection and intensity of transmission and the development of protective IgE responses to these antigens, thus improving our knowledge of the mechanisms by which protective host immune responses develop. This knowledge will be critical in understanding how control efforts such as mass drug administration campaigns influence the development of host immunity and subsequent patterns of infection and disease within endemic populations.

A cercarial invadolysin interferes with the host immune response and facilitates infection establishment of Schistosoma mansoni

Schistosoma mansoni employs immune evasion and immunosuppression to overcome immune responses mounted by its snail and human hosts. Myriad immunomodulating factors underlie this process, some of which are proteases. Here, we demonstrate that one protease, an invadolysin we have termed SmCI-1, is released from the acetabular glands of S. mansoni cercaria and is involved in creating an immunological milieu favorable for survival of the parasite. The presence of SmCI-1 in the cercarial stage of S. mansoni is released during transformation into the schistosomula. SmCI-1 functions as a metalloprotease with the capacity to cleave collagen type IV, gelatin and fibrinogen. Additionally, complement component C3b is cleaved by this protease, resulting in inhibition of the classical and alternative complement pathways. Using SmCI-1 knockdown cercariae, we demonstrate that SmCI-1 protects schistosomula from complement-mediated lysis in human plasma. We also assess the effect of SmCI-1 on cytokine release from human peripheral blood mononuclear cells, providing compelling evidence that SmCI-1 promotes an anti-inflammatory microenvironment by enhancing production of IL-10 and suppressing the production of inflammatory cytokines like IL-1B and IL-12p70 and those involved in eosinophil recruitment and activation, like Eotaxin-1 and IL-5. Finally, we utilize the SmCI-1 knockdown cercaria in a mouse model of infection, revealing a role for SmCI-1 in S. mansoni survival.

Differential proteomic analysis of laser-microdissected penetration glands of avian schistosome cercariae with a focus on proteins involved in host invasion

Schistosome invasive stages, cercariae, leave intermediate snail hosts, penetrate the skin of definitive hosts, and transform to schistosomula which migrate to the final location. During invasion, cercariae employ histolytic and other bioactive products of specialized holocrine secretory cells - postacetabular (PA) and circumacetabular (CA) penetration glands. Although several studies attempted to characterize protein composition of the in vitro-induced gland secretions in Schistosoma mansoni and Schistosoma japonicum, the results were somewhat inconsistent and dependent on the method of sample collection and processing. Products of both gland types mixed during their secretion did not allow localization of identified proteins to a particular gland. Here we compared proteomes of separately isolated cercarial gland cells of the avian schistosome Trichobilharzia szidati, employing laser-assisted microdissection and shotgun LC-MS/MS, thus obtaining the largest dataset so far of the representation and localization of cercarial penetration gland proteins. We optimized the methods of sample processing with cercarial bodies (heads) first. Alizarin-pre-stained, chemically non-fixed samples provided optimal results of MS analyses, and enabled us to distinguish PA and CA glands for microdissection. Using 7.5 x 10⁶ μm³ sample volume per gland replicate, we identified 3347 peptides assigned to 792 proteins, from which 461 occurred in at least two of three replicates in either gland type (PA = 455, 40 exclusive; CA = 421, six exclusive; 60 proteins differed significantly in their abundance between the glands). Peptidases of five catalytic types accounted for ca. 8% and 6% of reliably identified proteins in PA and CA glands, respectively. Invadolysin, nardilysin, cathepsins B2 and L3, and elastase 2b orthologs were the major gland endopeptidases. Two cystatins and a serpin were highly abundant peptidase inhibitors in the glands. While PA glands generally had rich enzymatic equipment, CA glands were conspicuously abundant in venom allergen-like proteins.

Schistosoma mansoni Larval Extracellular Vesicle protein 1 (SmLEV1) is an immunogenic antigen found in EVs released from pre-acetabular glands of invading cercariae

Extracellular Vesicles (EVs) are an integral component of cellular/organismal communication and have been found in the excreted/secreted (ES) products of both protozoan and metazoan parasites. Within the blood fluke schistosomes, EVs have been isolated from egg, schistosomula, and adult lifecycle stages. However, the role(s) that EVs have in shaping aspects of parasite biology and/or manipulating host interactions is poorly defined. Herein, we characterise the most abundant EV-enriched protein in Schistosoma mansoni tissue-migrating schistosomula (Schistosoma mansoni Larval Extracellular Vesicle protein 1 (SmLEV1)). Comparative sequence analysis demonstrates that lev1 orthologs are found in all published Schistosoma genomes, yet homologs are not found outside of the Schistosomatidae. Lifecycle expression analyses collectively reveal that smlev1 transcription peaks in cercariae, is male biased in adults, and is processed by alternative splicing in intra-mammalian lifecycle stages. Immunohistochemistry of cercariae using a polyclonal anti-recombinant SmLEV1 antiserum localises this protein to the pre-acetabular gland, with some disperse localisation to the surface of the parasite. S. mansoni-infected Ugandan fishermen exhibit a strong IgG1 response against SmLEV1 (dropping significantly after praziquantel treatment), with 11% of the cohort exhibiting an IgE response and minimal levels of detectable antigen-specific IgG4. Furthermore, mice vaccinated with rSmLEV1 show a slightly reduced parasite burden upon challenge infection and significantly reduced granuloma volumes, compared with control animals. Collectively, these results describe SmLEV1 as a Schistosomatidae-specific, EV-enriched immunogen. Further investigations are now necessary to uncover the full extent of SmLEV1's role in shaping schistosome EV function and definitive host relationships.

The Transcriptome of Schistosoma mansoni Developing Eggs Reveals Key Mediators in Pathogenesis and Life Cycle Propagation

Schistosomiasis, the most important helminthic disease of humanity, is caused by infection with parasitic flatworms of the genus Schistosoma. The disease is driven by parasite eggs becoming trapped in host tissues, followed by inflammation and granuloma formation. Despite abundant transcriptome data for most developmental stages of the three main human-infective schistosome species—Schistosoma mansoni, S. japonicum and S. haematobium—the transcriptomic profiles of developing eggs remain under unexplored. In this study, we performed RNAseq of S. mansoni eggs laid in vitro during early and late embryogenesis, days 1-3 and 3-6 post-oviposition, respectively. Analysis of the transcriptomes identified hundreds of up-regulated genes during the later stage, including venom allergen-like (VAL) proteins, well-established host immunomodulators, and genes involved in organogenesis of the miracidium larva. In addition, the transcriptomes of the in vitro laid eggs were compared with existing publicly available RNA-seq datasets from S. mansoni eggs collected from the livers of rodent hosts. Analysis of enriched GO terms and pathway annotations revealed cell division and protein synthesis processes associated with early embryogenesis, whereas cellular metabolic processes, microtubule-based movement, and microtubule cytoskeleton organization were enriched in the later developmental time point. This is the first transcriptomic analysis of S. mansoni embryonic development, and will facilitate our understanding of infection pathogenesis, miracidial development and life cycle progression of schistosomes.

Schistosoma mansoni venom allergen-like protein 6 (SmVAL6) maintains tegumental barrier function

•

Smval6 is expressed in oral/ventral suckers, oesophageal gland and mesenchymal cells of Schistosoma mansoni.

•

Smval6 knockdown increases surface membrane permeability.

•

SmVAL6 interacts with Sm14 and DLC proteins.

The Schistosoma mansoni venom allergen-like protein (SmVAL) superfamily is a collection of at least 29 molecules that have been classified into two distinctive groups (Group 1 and Group 2 SmVALs). The fundamental basis for SmVAL segregation relates to signal peptide and conserved cysteine retention (present in all Group 1 SmVALs, but absent in all Group 2 SmVALs). These structural differences have led to the hypothesis that most Group 1 SmVALs, found as components of schistosome excretory/secretory (E/S) products, predominantly interact with their environment (intermediate or definitive hosts) whereas the Group 2 SmVALs are retained within the schistosome to fulfil parasite-related functions. While experimental evidence to support Group 1 SmVAL/host interactions is growing, similar support for identification of parasite-related Group 2 SmVAL functions is currently lacking. By applying a combination of approaches to the study of SmVAL6, we provide the first known evidence for an essential function of a Group 2 SmVAL in schistosome biology. After whole mount in situ hybridisation (WISH) localised Smval6 to the anterior region of the oesophageal gland (AOG) and cells scattered through the mesenchyme in adult schistosomes, short interfering RNA (siRNA)-mediated silencing of Smval6 was employed to assess loss of function phenotypes. Here, siSmval6-mediated knockdown of transcript and protein levels led to an increase in tegumental permeability as assessed by the quantification of TAMRA-labelled dextran throughout sub-tegumental cells/tissues. Yeast two hybrid screening using SmVAL6 as a bait revealed Sm14 (a fatty acid binding protein) and a dynein light chain (DLC) as directly interacting partners. Interrogation of single-cell RNA-seq (scRNA-seq) data supported these protein interactions by demonstrating the spatial co-expression of Smval6/dlc/Sm14 in a small proportion of adult cell types (e.g. neurons, tegumental cells and neoblasts). In silico modelling of SmVAL6 with Sm14 and DLC provided evidence that opposing faces of SmVAL6 were likely responsible for these protein/protein interactions. Our results suggest that SmVAL6 participates in oesophageal biology, formation of higher order protein complexes and maintenance of tegumental barrier function. Further studies of other Group 2 SmVALs may reveal additional functions of this enigmatic superfamily.