Immune modulation of buffalo peripheral blood mononuclear cells by two asparaginyl endopeptidases from Fasciola gigantica

Abstract

Background Fascioliasis is a zoonotic parasitic disease caused by Fasciola hepatica and Fasciola gigantica, which poses a serious threat to global public health and livestock farming. Fasciola gigantica secretes and excretes various components to manipulate the immune response, thereby enhancing its invasion, migration, and survival in vivo. However, the roles of specific components in immune modulation, such as asparagine endopeptidase, remain unknown. Methods The transcriptional abundance of members of the asparagine endopeptidase family (also known as the legumain family) from F. gigantica was analyzed. Two highly transcribed asparagine endopeptidases in metacercariae, juveniles and adults were cloned, and their recombinant proteins—recombinant F. gigantica legumain (rFgLGMN-1) and (rFgLGMN-2)—were expressed in prokaryotic expression system. Their regulatory effects on buffalo peripheral blood mononuclear cells (PBMCs), including proliferation, migration, total nitric oxide (NO) production, cytokine secretion, and phagocytosis were explored in vitro. Results Ten members of the legumain family were detected in F. gigantica, among of which FgLGMN-1 and FgLGMN-2 exhibited high transcription levels in juveniles and adults. The isolation of sequences indicated that FgLGMN-1 encodes 409 amino acids, while FgLGMN-2 encodes 403 amino acids. Both recombinant FgLGMN-1 (rFgLGMN-1) and rFgLGMN-2 were recognized by serum from buffaloes infected with F. gigantica. Both rFgLGMN-1 and rFgLGMN-2 inhibited the proliferation of PBMCs, and rFgLGMN-1 also inhibited the migration of PBMCs. While rFgLGMN-1 increased the production of total NO, rFgLGMN-2 decreased NO production. Both rFgLGMN-1 and rFgLGMN-2 increased the transcription of the cytokines interleukin-10 and transforming growth factor β. The effect of rFgLGMN-1 and rFgLGMN-2 on the phagocytosis of PBMCs varied depending on their concentrations. Conclusions rFgLGMN-1 and rFgLGMN-2 modulate several cellular and immunological functions of PBMCs, and exhibited distinct regulatory effects on these in vitro, which indicated that they may play roles in immune modulation and facilitate fluke development. However, due to uncertainties associated with in vitro experiments, further studies are necessary to elucidate the precise functions of these legumains. Graphical Abstract