The major role of junctional diversity in the horse antibody repertoire.

This research provides a detailed examination of the antibody diversity in horses, particularly emphasizing the importance of junctional diversity. Utilizing next generation sequencing, the study found that while horses can use all functional IGHV genes, the majority of their antibodies use a limited selection, and the diversity is significantly enriched by junctional diversity.

Study Design and Findings

The study began by conducting a profound investigation into the antigen B cell receptor diversity of non-infected adult horses. This was achieved by applying Next Generation Sequencing (NGS), a powerful technology providing deep and quantitative analysis that allows researchers to explore adaptive immunity in health and disease:

• The NGS study yielded a mean of 248,169 unique IgM clones and 66,141 unique IgG clones in the four horses that were studied.
• Coverage analysis indicated that the sequence coverage was between 52% and 82% for IgM and IgG isotypes, indicating that the sequencing effort was adequate to capture a large proportion of the repertoire.
• The study observed that while horses’ antibodies can use all functional IGHV genes, the majority of their antibodies – about 80% – use only three IGHV gene segments.
• A narrowing of diversity was also observed in the fact that around 55% of their antibodies use only one IGHJ gene segment.

Junctional Diversity and its Role

The limited diversity as observed in the above findings is significantly compensated by junctional diversity in horse antibodies:

• Junctional diversity was found in over 90% of horse antibodies, showcasing its ubiquity and importance in the equine antibody repertoire.
• The study also highlighted that the junctional region length in horse antibodies appears to be longer than in other species, suggesting a stronger role for junctional diversity in providing variability in horses.
• The range of N1 and N2 nucleotides addition was observed to vary between 0 to 111 nucleotides, thereby reinforcing this hypothesis.
• Significantly, around 45% of the antibody clones were found to have more than ten nucleotides in both the N1 and N2 junction regions.

Based on these findings, the study puts forward that junctional diversity may be one of the most crucial mechanisms providing variability to the equine antibody repertoire.

Conclusions and Future Recommendations

The study offers fresh insights on horse antibody composition, how its diversity is generated, and its unique characteristics compared to other species. This includes details about the frequency and length of N nucleotide addition. The research also signals the need for more studies to better characterize TdT in horses and other species for gaining further understanding of the antibody repertoire characteristics.