Abstract
Unlike the successful immunization of native H. contortus antigens that contributed to the realization of the first commercial vaccine Barbervax, not many studies revealed the encouraging protective efficacies of recombinant H. contortus antigens in laboratory trials or under field conditions. In our preliminary study, H. contortus α/β-hydrolase domain protein (HcABHD) was demonstrated to be an immunomodulatory excretory–secretory (ES) protein that interacts with goat T cells. We herein evaluated the protective capacities of two HcABHD preparations, recombinant HcABHD (rHcABHD) antigen and anti-rHcABHD IgG, against H. contortus challenge via active and passive immunization trials, respectively. Parasitological parameter, antibody responses, hematological pathology and cytokine profiling in unchallenged and challenged goats were monitored and determined throughout both trials. Subcutaneous administration of rHcABHD with Freund adjuvants elicited protective immune responses in challenged goats, diminishing cumulative fecal egg counts (FEC) and total worm burden by 54.0% and 74.2%, respectively, whereas passive immunization with anti-rHcABHD IgG conferred substantial protection to challenged goats by generating a 51.5% reduction of cumulative FEC and a 73.8% reduction of total worm burden. Additionally, comparable changes of mucosal IgA levels, circulating IgG levels, hemoglobin levels, and serum interleukin (IL)-4 and IL-17A levels were observed in rHcABHD protein/anti-rHcABHD IgG immunized goats in both trials. Taken together, the recombinant version of HcABHD might have further application under field conditions in protecting goats against H. contortus infection, and the integrated immunological pipeline of ES antigen identification, screening and characterization may provide new clues for further development of recombinant subunit vaccines to control H. contortus.
Highlights
Haemonchus contortus is a highly pathogenic gastrointestinal nematode with a developmental life cycle including three free-living larval stages and two parasitic stages
A single band ~ 36 kDa was observed through the specific recognition of the recombinant HcABHD (rHcABHD) protein by goat anti-rHcABHD sera (Additional file 1B, Lane 3), whereas no positive band was identified by goat pre-immunization sera (Additional file 1B, Lane 4)
Vaccinations of these native antigens appear to bring in much higher protective efficacy to H. contortus challenge rather than their synthetic or recombinant forms that had compromised or partial protective capacity attributed to lack of post-translational modifications or inaccurate suboptimal folding [30,31,32]
Summary
Haemonchus contortus is a highly pathogenic gastrointestinal nematode with a developmental life cycle including three free-living larval stages and two parasitic stages. This parasitic nematode resides in the abomasum of ruminants, in sheep and goats, Lu et al Vet Res (2021) 52:3 with the occurrence of global anthelmintic-resistance, alternative nonchemical strategies are imperative to be developed and employed for the increasing demands of drug-free animal production [3]. In 2014, the first commercially available vaccine Barbervax encompassing enriched native gutderived antigens H-gal-GP and H11 was authorized in Australia and produced at an industrial scale via H. contortus harvested from donor sheep based on processing and production technology [4]. As Barbervax is made up of native hidden antigens that rely on frequent boosting to generate high levels of circulating antibodies, the development of alternative vaccines like recombinant subunit vaccines still needs to be further investigated
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