Analysis of the Expressed Porcine Antibody Repertoire in Porcine and Reproductive and Respiratory Syndrome Virus (PRRSV) Infected Pigs

Adaptive humoral immunity is mediated by one heavy chain and two light chain loci that encode multiple gene segments which recombine to generate a potentially vastly diverse antigen-binding repertoire.  We characterized the diversity of porcine heavy and light chain repertoires in pigs that were infected or uninfected with porcine reproductive and respiratory syndrome virus (PRRSV) using amplicon-based 454 high-throughput sequencing. Bioinformatic analysis of heavy and light chain reads revealed that a small number of variable gene segments dominate the expression of the immunoglobulin repertoire. Total richness was estimated at approximately 3.5x10⁵ for heavy chain, 1.5x10⁵ for kappa light chain, and 2.3x10⁵ for lambda light chain. The calculated richness is similar to humans, suggesting that the swine antigen-binding repertoire is similarly complex, despite lack of diversity in the porcine IGHV framework regions.  Further, differential heavy chain variable (IGHV) gene segment usage was identified between PRRSV-infected and uninfected pigs. Among both heavy and light chain transcripts, several exceptionally common immunoglobulin sequences were identified in PRRSV-infected pigs which were rare in uninfected pigs, indicating that we detected clonally expanded PRRSV-specific B-cells. Allelic heterogeneity was detected among pigs in the lambda light chain locus, including the identification of a novel IGLV3 gene segment. The combination of allelic variation, differential gene segment usage, and somatic hypermutation may result in variable humoral immune responses that could predict efficacy of protection against PRRSV infection and disease.