TSCT is a significant public health issue, and developing countries and regions still face enormous challenges in the prevention and control of TSCT [2, 37]. When the pig cysticercus parasitizes the host, it can secrete and excrete certain products known as ESAs, which play a crucial role in the host-parasite interaction and immune regulation. Previous studies have shown that these antigens possess immunomodulatory properties and can influence the host immune response by inducing the production of immune-suppressive Treg cells, thereby aiding the pig cysticercus in evading the host's immune attacks [38]. The composition of pig cysticercus ESAs is complex, and with the advancement of proteomics research and application in the field of cestodes [39, 40], our research group has conducted proteomic analysis of pig cysticercus ESAs. As a result, a immune-active protein called TPx, which belongs to the peroxiredoxin superfamily, was successfully identified. TPx not only serves as a specific diagnostic antigen and a candidate vaccine antigen, but also induces macrophage polarization and Th immune responses [18]. Further analysis through GO functional annotation revealed that TPx protein is detected in immune system processes and is localized in the cytoplasm. Literature review indicates that TPx protein can bind to cell membrane surface receptors and exert its function intracellularly. TPx protein in pig cysticercus ESAs can stimulate an increase in the number of CD4 + T cells, CD8 + T cells, and CD4 + CD25 + Foxp3 + Treg cells in normal piglet PBMC, inducing T cell immune dysfunction and the generation of negative immune responses [21]. However, current research has only focused on this phenomenon, and the molecular mechanisms by which TPx protein regulates the imbalance of host Treg/Th17 cell equilibrium in pig cysticercus ESAs have not been fully elucidated. Therefore, we used transcriptomics to investigate the molecular mechanisms by which TPx protein in pig cysticercus ESAs regulates piglet Treg/Th17 cell differentiation through the TGF-β signaling pathway.
In the field of parasitology, transcriptomics has become an important tool [32–34]. Differential transcriptomics, as a crucial branch of transcriptomics, provides a new perspective and method for us to gain a deeper understanding of the biological characteristics, parasitic mechanisms, and interactions with the host in parasites. In this study, differential transcriptome analysis was employed to explore the signaling pathways by which TPx protein in pig cysticercus ESAs affects the imbalance of Treg/Th17 cells. The differentially expressed genes were analyzed through GO enrichment and KEGG pathway analysis. It was found that recombinant TPx protein in pig cysticercus can induce changes in T cell immune processes, cell differentiation, and signaling molecules in Jurkat cells. However, through KEGG pathway enrichment, it was discovered that these differentially expressed genes are primarily involved in T cell biological responses, catalytic activity, and metabolic processes, such as positive regulation of cytoplasmic calcium ion concentration, inflammatory responses, DNA-binding transcription factor activity, cell division, regulation of cyclin-dependent protein serine/threonine kinase activity, cellular protein metabolic process, and signaling receptor binding. Therefore, we further conducted GSEA analysis on these differentially expressed genes based on the KEGG database. GSEA enrichment analysis has several advantages in studying signaling pathways. It not only comprehensively considers gene expression patterns but also possesses good biological interpretability and integration, which helps to reveal the functions and interactions of gene sets in specific biological processes.
Treg cells and Th17 cells play opposing roles in the immune response to parasitic infections, and the imbalance between them has been observed in various parasitic infection diseases and models. Maintaining the balance of Treg/Th17 cells is crucial for maintaining the stable immune state of the host following parasitic infection [14]. It has been found that the TGF-β signaling pathway regulates the balance of Treg/Th17 cells through its downstream signaling molecule, the Smad protein. For example, in a mouse model of cysticercosis caused by Echinococcus granulosus (Eg), the percentage of splenic CD4 + Treg cells, Foxp3 mRNA transcription levels, and serum TGF-β1 levels increase. Subsequently, treatment of the model mice with the inhibitor SB-525334 leads to significant reductions in the percentage of splenic CD4 + Treg cells and phosphorylation levels of Smad2/3 proteins compared to the E. granulosus-infected group. This indicates that in the mouse model of cysticercosis, the inhibitor SB-255334 inhibits Smad2/3 phosphorylation, blocks the TGF-β/Smad signaling pathway, reduces IL-10 secretion, and inhibits Treg cell differentiation (Yin et al. 2017). In a mouse model of alveolar echinococcosis caused by Echinococcus multilocularis (Em), it was found that during the early phase of infection (day 2 to day 30), the mRNA expression levels of Smad7 in mouse liver tissue significantly increase, while there is no significant difference in the number and ratio of Treg and Th17 cells in peripheral blood compared to the control group. During the middle phase of infection (day 30 to day 90), the mRNA expression levels of TβRI, TβRII, p-Smad2/3, and IL-17 all significantly increase, and both the number of Treg cells and Th17 cells increase. During the late phase of infection (day 90 to day 270), the number of Treg cells significantly increases, serum TGF-β and IL-10 levels rise, the number of Th17 cells decreases significantly, and the Treg/Th17 cell ratio completely reverses. This suggests that during the early phase of alveolar echinococcosis infection, Smad7 expression is upregulated to block the translocation of Smad2/3 complexes into the nucleus and TGF-β signaling. During the middle phase of infection, the TGF-β/Smad signaling pathway is activated, leading to the upregulation of TβRI, TβRII, p-Smad2/3, and the induction of a large amount of IL-17A by the host, resulting in a predominantly Th17 immune response. In the late phase of infection, the TGF-β/Smad signaling pathway promotes the differentiation of naive T cells into Treg cells, alleviating the Th17 cell-mediated immune response in the later stages. This imbalance in Treg/Th17 cell immune regulation favors the parasite's evasion of the host's immune response in the later stages of infection [42].
In this study, transcription factor and target gene prediction analysis was performed on the differentially expressed transcriptome data to identify and predict the transcription factors and their potential target genes involved in the differential expression. Through comparing the differential data between the 24-hour experimental group and the control group, the 48-hour experimental group and the 24-hour experimental group, and the 72-hour experimental group and the 48-hour experimental group, TGF-β was identified as a common differentially expressed target gene in all three groups, suggesting its potential role in regulating Treg and Th17 cell differentiation. The differential transcription factors, FOXA2, FOXH1, and FOXM1, belong to the Forkhead-box (FOX) gene family. They act as both transcriptional activators and repressors, as well as pioneer factors, interacting with other transcription factors and epigenetic effectors [43, 44]. Forkhead box proteins are important components of the TGF-β/Smad signaling pathway [45]. FOXA2 is important for maintaining the balance of effector cell differentiation in T cells. FOXA2 in thymic epithelial cells (TECs) can promote positive selection of conventional CD4 T cells and regulate the generation and activity of Treg cells [46]. Conditional deletion of FOXA2 in T cells aggravates Th2 inflammation, increases differentiation towards Th2, and inhibits CD4 T cell differentiation towards Th1 in vitro [47]. FOXH1 (also known as FAST, forkhead activin signal transducer) is a transcriptional activation factor that plays an important role as a signaling intermediate of TGF-β family members (such as Activin and Nodal). It is involved in the recruitment of SMAD3, SMAD2, and SMAD4 to form trimeric complexes [48]. The aryl hydrocarbon receptor (AHR), a member of the bHLH-PAS family, is a basic helix-loop-helix transcription factor activated through cognate ligand binding [49]. AHR plays a key regulatory role in the differentiation of Treg and Th17 cells. Studies have found that the expression of AhR in CD4 + T cells leads to a significant increase in the percentage of Treg and related gene transcripts (including Foxp3, IL-10, and CD39), and a significant decrease in the transcription of Th17 cells and related genes (including RORγt, IL-17A, and IL-17F), inducing an imbalance between Th17 and Treg cells [49, 50].
In this study, we also identified through GSEA that the TPx protein in Cysticercus cellulosae ESAs can inhibit the differentiation of Jurkat cells into Th17 cells at 24, 48, and 72 hours time points. In the differentially expressed genes enriched during Th17 cell differentiation, it was found that the TGF-β/Smad signaling pathway can promote the expression of the Foxp3 transcription factor, which in turn inhibits the expression of the ROR-γt transcription factor, thereby suppressing Th17 cell differentiation [29]. This indicates that the TPx protein in Cysticercus cellulosae ESAs is involved in regulating the balance of host Treg/Th17 cells and subsequently modulating the host immune response. These findings provide insights into the pathogenesis of cysticercosis.
The above research is confined to the level of differential transcriptomics. In future studies, we will further investigate the impact of the TPx protein in Cysticercus cellulosae ESAs on the balance of host Treg/Th17 cells using flow cytometry. We will also employ techniques such as inhibitors (ALK5 inhibit or/Smad7) to systematically validate the potential mechanisms through which the TPx protein affects the TGF-β signaling pathway and Th17 cell differentiation. These efforts aim to provide a foundation for understanding the host immune response to Cysticercus cellulosae infection and the immune evasion mechanisms of Cysticercus cellulosae.