Characterization of the Lambda Light Chain Repertoire and Non-Coding Regions of Equine Immunoglobulins Using the EquCab3 Genome

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 lambda light chain immunoglobulins (IgLambda), which constitute over 90% of circulating antibodies. Despite the sequencing of the equine genome, the International ImMunoGeneTics information system (IMGT) has yet to annotate IgLambda in its database, restricting the analysis of the horse antibody repertoire.In this study, we analyzed the equine IgLambda repertoire and inferred details about the promoter regions based on conserved human sequences. By utilizing a library composed of EquCab2 and EquCab3 assemblies, we annotated approximately 20% more IgLambda sequences than when using only EquCab2. With the identification of new functional alleles, we annotated nearly 12% more reads for the V gene segments. Notably, the annotation of the J segment IGLJ4S1*01 covers almost 50% of the repertoire, in contrast to the previously annotated J segment IGLJ4S1P*02, which represented only 0.05%. Our analysis also revealed a threefold increase in the quantity of clones compared to previous studies, with a preferential gene usage of 85% for V gene segments within subgroup 8 and 50% for IGLJ4S1*01. This preference may be attributed to a unique feature of their promoter, which contains an E-box adjacent to a consensus octamer.Additionally, our analysis indicated that the CDR-L3 region predominantly displays lengths of 10 to 11 amino acids, with serine (Ser) being the most common amino acid. This amino acid may play a role in antigen binding.Beyond enhancing the annotation and characterization of the equine IgLambda repertoire, this study also identified non-coding regions, particularly promoter regions and their elements, such as a conserved TATA-Box, octamer, a pyrimidine-rich region, and an E-box. The findings of this research contribute to a better understanding of equine IgLambda composition, gene usage, and promoter characteristics, ultimately advancing future studies involving the use of equine antibodies.