Characterization of the lambda light chain repertoire and non-coding regions of equine immunoglobulins using the EquCab3 genome

Abstract

Horse immunoglobulins have been utilized for over a century in serotherapy to treat venomous animal bites and various other conditions. However, molecular-level information about these immunoglobulins remains limited, particularly regarding immunoglobulin lambda light chains (Igλ), which constitute over 90 % of circulating antibodies. Despite the sequencing of the equine genome, the International ImMunoGeneTics information system (IMGT) has not yet annotated Igλ in its database, restricting the analysis of the horse antibody repertoire. In this study, we analyzed the equine Igλ repertoire and inferred the characteristics of the promoter regions and nearby co-stimulatory elements based on conserved human sequences. We find that some motifs from the promoter region of horse immunoglobulins showed a high rate of conservation between human and equine sequences, as an example of the octamer region. By mapping the V and J gene segment positions from EquCab2 to their corresponding positions in EquCab3, we constructed a library with new potential alleles. This impacted the annotation, since we identified the J gene segment J4S1^*01, which shares the same sequence as the J5 and J6S1 gene segments, account for over 50 % of the annotated J genes. Our analysis, which included a 2-fold increase in the number of clones compared to previous studies, revealed a restricted use of V gene segments, with approximately 70 % of the repertoire derived from just four gene segments within subgroup 8. This preference can be attributed to the presence of several co-stimulatory elements near the promoter region. Additionally, our analysis indicated that the CDR-L3 region predominantly displays lengths of 10–11 amino acids, with serine (Ser) being the most common amino acid. Beyond enhancing the annotation and characterization of the equine Igλ repertoire, this study also identified non-coding regions, particularly promoter regions containing a conserved octamer and a TATA-Box, and their co-stimulatory elements, such as pyrimidine-rich region, and E-box. The findings of this research contribute to a better understanding of equine Igλ composition, gene usage, and promoter characteristics, ultimately advancing future studies involving the use of equine antibodies.