Enzymes involved in trehalose-chitin synthesis in Haemonchus contortus could be vaccine candidates for goats.

Background: Trehalose-6-phosphate synthase (HcTPS) and trehalose-6-phosphate phosphatase (HcGOB) are key enzymes for trehalose synthesis in Haemonchus contortus. In addition, previous studies have also demonstrated that HcTPS and HcGOB can regulate the function of host immune cells in vitro, and are important immunosuppressive molecules. Therefore, this study evaluated the potential of HcTPS and HcGOB as vaccine candidates through in vitro and in vivo experiments.

Methods: To evaluate the inhibitory effects of polyclonal antibodies on egg hatching and larval development, anti-rHcTPS and anti-rHcGOB antibodies were incubated separately with eggs and first-stage larvae (L1s) under controlled in vitro conditions. For immunization studies, recombinant proteins (rHcTPS and rHcGOB) were formulated with Quil-A adjuvant, and administered to goats through subcutaneous injection. Vaccine efficacy against Haemonchus contortus infection was determined through comprehensive analysis of multiple parasitological parameters, including: (1) egg abnormality rate, (2) hatching success rate, (3) reduction egg output rates, and (4) reduction in adult worm burden.

Results: The results of in vitro experiments showed that polyclonal antibodies against HcTPS and HcGOB had no effect on the hatching rate of eggs, but significantly affected the development from L1s to infectious third stage larvae (L3s). After immunization with recombinant HcTPS protein (rHcTPS) and recombinant HcGOB protein (rHcGOB), high levels of antigen-specific immunoglobulin G (IgG) were produced in goats, and remained till the end of the experiment. Compared with the Quil-A adjuvant control group, the number of deformed eggs in the rHcTPS protein- immunized group and the rHcGOB protein- immunized group were significantly increased. In the rHcTPS protein-immunized group and the rHcGOB protein-immunized group, the deformity rate of eggs was 9.59% and 17.30%, respectively, and the hatching rate of eggs was reduced by 11.27% and 13.71%, respectively. Moreover, compared with the Quil-A adjuvant control group, the number of eggs and adults in the HcTPS protein- immunized group decreased by 64.47% and 60.93%, respectively, and the number of eggs and adults in the rHcGOB protein- immunized group decreased by 63.97% and 69.54%, respectively. Furthermore, compared with the control group (Quil-A adjuvant), the trehalose content in the rHcTPS protein- immunized group and the rHcGOB protein- immunized group was also significantly reduced.

Conclusions: These findings indicate that rHcTPS and rHcGOB exhibit superior immune protective effects, rendering them promising candidates for vaccine development.