Bovine Natural Antibody Relationships to Specific Antibodies and Fasciola hepatica Burdens after Experimental Infection and Vaccination with Glutathione S-Transferase

Antigen specificity affects analysis of natural antibodies

Natural antibodies are used to compare immune systems across taxa, to study wildlife disease ecology, and as selection markers in livestock breeding. These immunoglobulins are present prior to immune stimulation. They are described as having low antigen specificity or polyreactive binding and are measured by binding to self-antigens or novel exogenous proteins. Most studies use only one or two antigens to measure natural antibodies and ignore potential effects of antigen specificity in analyses. It remains unclear how different antigen-specific natural antibodies are related or how diversity among natural antibodies may affect analyses of these immunoglobulins. Using genetically distinct lines of chickens as a model system, we tested the hypotheses that (1) antigen-specific natural antibodies are independent of each other and (2) antigen specificity affects the comparison of natural antibodies among animals. We used blood cell agglutination and enzyme-linked immunosorbent assays to measure levels of natural antibodies binding to four antigens: (i) rabbit erythrocytes, (ii) keyhole limpet hemocyanin, (iii) phytohemagglutinin, or (iv) ovalbumin. We observed that levels of antigen specific natural antibodies were not correlated. There were significant differences in levels of natural antibodies among lines of chickens, indicating genetic variation for natural antibody production. However, line distinctions were not consistent among antigen specific natural antibodies. These data show that natural antibodies are a pool of relatively distinct immunoglobulins, and that antigen specificity may affect interpretation of natural antibody function and comparative immunology.

The Detection of Circulating Antigen Glutathione S-Transferase in Sheep Infected with Fasciola hepatica with Double-Antibody Sandwich Signal Amplification Enzyme-Linked Immunosorbent Assay

Fasciolosis is a global zoonotic parasitic disease caused by F. hepatica infection that is particularly harmful to cattle and sheep. A biotin-streptavidin signal amplification ELISA (streptavidin-ELISA/SA-ELISA) based on circulating antigens can allow for the early detection of F. hepatica-infected animals and is suitable for batch detection. It is considered to be a better means of detecting F. hepatica infection than traditional detection methods. In this study, using the serum of sheep artificially infected with F. hepatica, the cDNA expression library of F. hepatica was screened, 17 immunodominant antigen genes of F. hepatica were obtained, and glutathione s-transferase (GST) was selected as the candidate detection antigen. Firstly, the GST cDNA sequence was amplified from F. hepatica, followed by the preparation of recombinant protein GST (rFhGST). Then, monoclonal and polyclonal antibodies against rFhGST were prepared using the GST protein. Afterward, the immunolocalization of the target protein in the worm was observed via confocal microscopy, and it was found that the GST protein was localized in the uterus, intestinal tract, and body surface of F. hepatica. Finally, a double-antibody sandwich SA-ELISA based on the detection of circulating antigens was established. There was no cross-reaction with positive sera infected with Dicrocoelium lanceatum (D. lanceatum), Haemonchus contortus (H. contortus), Neospora caninum (N. caninum), or Schistosoma japonicum (S. japonicum). Forty serum and fecal samples from the same batch of sheep in Nong'an County, Changchun City, Jilin Province, China were analyzed using the established detection method and fecal detection method. The positive rate of the SA-ELISA was 17.5%, and the positive rate of the fecal detection method was 15%. The detection results of this method were 100% consistent with commercial ELISA kits. A total of 152 sheep serum samples were tested in Nong'an County, Changchun City, Jilin Province, and the positive rate was 5.92%. This study laid the foundation for the development of serological detection preparations for F. hepatica infection based on the detection of circulating antigens.

Levels of Circulating IgM and IgY Natural Antibodies in Broiler Chicks: Association with Genotype and Farming Systems

Naturally occurring antibodies (NAbs), which are major components of innate immunity, exist in circulation under healthy conditions without prior antigenic stimulation and are able to recognize both self- and non-self-constituents. The present study aimed at identifying potential immunological differences between commercial fast- and slow-growth broilers (n = 555) raised in conventional and free-range systems, respectively, through the use of the specificity, isotypes and levels of circulating NAbs. The possible beneficial effect of oregano-based dietary supplementation was also evaluated. To this end, serum IgM and IgY NAbs against self- (actin and DNA) and non-self- antigens (trinitrophenol and lipopolysaccharide) were measured by ELISA and further correlated with genotype, season and performance. Significantly higher levels of IgM NAbs against all antigens were found in slow-growth compared to fast-growth broilers. IgM NAb levels were also significantly increased in dietarily supplemented slow-growth broilers versus those consuming standard feed. Moreover, significantly elevated levels of anti-DNA IgY NAbs were found in fast-growth compared to slow-growth broilers, whereas the opposite was observed for anti-LPS IgY NAbs. Multivariate linear regression analysis confirmed multiple interactions between NAb levels, genotype, season and performance. Overall, serum NAbs have proven to be valuable innovative immunotools in the poultry industry, efficiently differentiating fast-growing versus slow-growing broilers, and dietary supplementation of plant extracts can enhance natural immunity.

Omics tools enabling vaccine discovery against fasciolosis

In the past decade significant advances in our understanding of liver fluke biology have been made through in-depth interrogation and analysis of evolving Fasciola hepatica and Fasciola gigantica omics datasets. This information is crucial for developing novel control strategies, particularly vaccines necessitated by the global spread of anthelmintic resistance. Distilling them down to a manageable number of testable vaccines requires combined rational, empirical, and collaborative approaches. Despite a lack of clear outstanding vaccine candidate(s), we must continue to identify salient parasite-host interacting molecules, likely in the secretory products, tegument, or extracellular vesicles, and perform robust trials especially in livestock, using present and emerging vaccinology technologies to discover that elusive liver fluke vaccine. Omics tools are bringing this prospect ever closer.