Dongqi Wu

Fasciola gigantica can modulate host immune mechanisms through excretory–secretory products (ESP). As one of the components of ESP, it is unknown whether Abelson tyrosine protein kinase (Abl) is involved in parasite–host immune interaction. To investigate the immunoregulatory function of Abl in Fasciola gigantica, we cloned and expressed the Fasciola gigantica Abl protein and assessed its effect on specific immune functions of buffalo peripheral blood mononuclear cells (PBMCs). Recombinant F. gigantica Abelson tyrosine protein kinase (rFgAbl) was expressed in Escherichia coli. Western blot analysis was performed to assess the reactivity of anti-rFgAbl antibodies with rFgAbl, serum from F. gigantica-infected buffalo, and excretion and secretion products of F. gigantica. Immunohistochemical analysis was conducted to determine the localization of FgAbl in tissues from larval stages and adult worms of F. gigantica. Furthermore, immunofluorescence analysis was utilized to evaluate the binding ability of the rFgAbl protein to buffalo peripheral blood mononuclear cells (PBMCs), as well as to investigate the effects of varying concentrations of rFgAbl protein (5, 10, 20, 40, and 80 μg/mL) on the functional responses of PBMCs. Anti-rFgAbl antibodies specifically recognize rFgAbl, serum from buffalo infected with F. gigantica, and FgESP. rFgAbl is localized in the cecum and capsule of juvenile worms, as well as in the testis and viellaria of adult worms. Additionally, rFgAbl enhances cell proliferation, migration, nitric oxide (NO) production, and phagocytosis, while also increasing the transcription levels of cytokines (IFN-γ, IL-12, TNF-α, IL-4, IL-10, and TGF-β). The results indicate that rFgAbl can influence the immune function of PBMCs. Further investigation into the immunomodulatory properties of the rFgAbl protein will enhance our understanding of the immune interaction mechanisms between trematodes and their hosts.

In the present study, we reconstructed the transforming growth factor beta (TGF-β) signaling pathway for Fasciola gigantica, which is a neglected tropical pathogen. We defined the components involved in the TGF-β signaling pathway and investigated the transcription profiles of these genes for all developmental stages of F. gigantica. In addition, the presence of these components in excretory and secretory products (FgESP) was predicted via signal peptide annotation. The core components of the TGF-β signaling pathway have been detected in F. gigantica; classical and nonclassical single transduction pathways were constructed. Four ligands have been detected, which may mediate the TGF-β signaling pathway and BMP signaling pathway. Two ligand-binding type II receptors were detected, and inhibitory Smad7 was not detected. TLP, BMP-3, BMP-1, and ActRIb showed higher transcription in 42-day juvenile and 70-day juvenile, while ActRIIa, Smad1, ActRIIb, Smad8, KAT2B, and PP2A showed higher transcription in egg. TLM, Ski, Smad6, BMPRI, p70S6K, Smad2, Smad3, TgfβRI, Smad4, and p300 showed higher transcription in metacercariae. Four ligands, 2 receptors and 3 Smads are predicted to be present in the FgESP, suggesting their potential extrinsic function. This study should help to understand signal transduction in the TGF-β signaling pathway in F. gigantica. In addition, this study helps to illustrate the complex mechanisms involved in developmental processes and F. gigantica — host interaction and paves the way for further characterization of the signaling pathway in trematodes.