Modulation of the Functions of Goat Peripheral Blood Mononuclear Cells by Fasciola gigantica Thioredoxin Peroxidase In Vitro

The liver fluke Fasciola gigantica has a remarkable ability to establish a long-term infection within the hepatobiliary system of the mammalian definitive host. F. gigantica achieves this by producing excretory–secretory molecules, which have immunomodulatory activities. In an effort to elucidate the immunomodulatory functions of F. gigantica thioredoxin peroxidase protein (FgTPx), we expressed recombinant FgTPx (rFgTPx) in Escherichia coli bacteria and examined its effects on several functions of goat peripheral blood mononuclear cells (PBMCs) in vitro. Sequence analysis revealed that FgTPx is related to a thioredoxin-like superfamily. Western blot analysis showed that rFgTPx was recognized by the sera of goats experimentally infected by F. gigantica. The specific binding of rFgTPx protein to the surface of goat PBMCs was demonstrated by immunofluorescence staining. We investigated the influence of serial concentrations of rFgTPx on various functions of goat PBMCs. All concentrations of rFgTPx increased the secretion of interleukin-2 (IL-2), IL-4, IL-10, IL-17, transforming growth factor-beta (TGF-β), and interferon gamma (IFN-γ), but inhibited PBMC proliferation, migration, and monocyte phagocytosis. Goat PBMCs exposed to 20–40 μg/mL of rFgTPx secreted increased levels of nitric oxide (NO), and 10–40 μg/mL of rFgTPx promoted cell apoptosis. These findings indicate that rFgTPx influences various functions of goat PBMCs by interacting with a large number of cellular targets, ultimately to promote the parasite’s survival. The roles of rFgTPx and their interacting proteins warrant further investigation.

Thioredoxin peroxidase secreted by Echinococcus granulosus (sensu stricto) promotes the alternative activation of macrophages via PI3K/AKT/mTOR pathway

Background Larvae of Echinococcus granulosus (sensu lato) dwell in host organs for a long time but elicit only a mild inflammatory response, which indicates that the resolution of host inflammation is necessary for parasite survival. The recruitment of alternatively activated macrophages (AAMs) has been observed in a variety of helminth infections, and emerging evidence indicates that AAMs are critical for the resolution of inflammation. However, whether AAMs can be induced by E. granulosus (s.l.) infection or thioredoxin peroxidase (TPx), one of the important molecules secreted by the parasite, remains unclear. Methods The activation status of peritoneal macrophages (PMs) derived from mice infected with E. granulosus (sensu stricto) was analyzed by evaluating the expression of phenotypic markers. PMs were then treated in vivo and in vitro with recombinant EgTPx (rEgTPx) and its variant (rvEgTPx) in combination with parasite excretory-secretory (ES) products, and the resulting activation of the PMs was evaluated by flow cytometry and real-time PCR. The phosphorylation levels of various molecules in the PI3K/AKT/mTOR pathway after parasite infection and antigen stimulation were also detected. Results The expression of AAM-related genes in PMs was preferentially induced after E. granulosus (s.s.) infection, and phenotypic differences in cell morphology were detected between PMs isolated from E. granulosus (s.s.)-infected mice and control mice. The administration of parasite ES products or rEgTPx induced the recruitment of AAMs to the peritoneum and a notable skewing of the ratio of PM subsets, and these effects are consistent with those obtained after E. granulosus (s.s.) infection. ES products or rEgTPx also induced PMs toward an AAM phenotype in vitro. Interestingly, this immunomodulatory property of rEgTPx was dependent on its antioxidant activity. In addition, the PI3K/AKT/mTOR pathway was activated after parasite infection and antigen stimulation, and the activation of this pathway was suppressed by pre-treatment with an AKT/mTOR inhibitor. Conclusions This study demonstrates that E. granulosus (s.s.) infection and ES products, including EgTPx, can induce PM recruitment and alternative activation, at least in part, via the PI3K/AKT/mTOR pathway. These results suggest that EgTPx-induced AAMs might play a key role in the resolution of inflammation and thereby favour the establishment of hydatid cysts in the host.

An ambiguous N-terminus drives the dual targeting of an antioxidant protein Thioredoxin peroxidase (TgTPx1/2) to endosymbiotic organelles in Toxoplasma gondii

Toxoplasma gondii harbors two endosymbiotic organelles: a relict plastid, the apicoplast, and a mitochondrion. The parasite expresses an antioxidant protein, thioredoxin peroxidase 1/2 (TgTPx1/2), that is dually targeted to these organelles. Nuclear-encoded proteins such as TgTPx1/2 are trafficked to the apicoplast via a secretory route through the endoplasmic reticulum (ER) and to the mitochondrion via a non-secretory pathway comprising of translocon uptake. Given the two distinct trafficking pathways for localization to the two organelles, the signals in TgTPx1/2 for this dual targeting are open areas of investigation. Here we show that the signals for apicoplast and mitochondrial trafficking lie in the N-terminal 50 amino acids of the protein and are overlapping. Interestingly, mutational analysis of the overlapping stretch shows that despite this overlap, the signals for individual organellar uptake can be easily separated. Further, deletions in the N-terminus also reveal a 10 amino acid stretch that is responsible for targeting the protein from punctate structures surrounding the apicoplast into the organelle itself. Collectively, results presented in this report suggest that an ambiguous signal sequence for organellar uptake combined with a hierarchy of recognition by the protein trafficking machinery drives the dual targeting of TgTPx1/2.