Shared epitopes among HLA class II alleles: gene conversion, common ancestry and balancing selection

Area of Science:

• Evolutionary biology
• Immunogenetics
• Molecular anthropology

Background:

• The human leukocyte antigen (HLA) class II genes exhibit extensive sequence polymorphism.
• Understanding the evolutionary forces shaping this diversity is crucial for evolutionary and immunogenetic studies.

Purpose of the Study:

• To investigate the evolutionary history and diversification patterns of primate HLA class II sequences.
• To explore the genetic mechanisms contributing to HLA class II polymorphism, including common ancestry, gene conversion, and convergent evolution.

Main Methods:

• Phylogenetic analysis of primate Major Histocompatibility Complex (MHC) class II sequences.
• Comparative sequence analysis to identify shared sequence motifs and patterns of polymorphism.

Main Results:

• Phylogenetic analysis indicates that HLA class II allelic lineages are ancient, predating hominoid species separation.
• Significant allelic diversification within these lineages occurred after species divergence, particularly for beta-chain loci.
• The observed patchwork polymorphism, with common sequence motifs across different alleles, can be explained by common ancestry, gene conversion, or convergent evolution.

Conclusions:

• HLA class II evolution is characterized by ancient lineage divergence followed by post-speciation diversification.
• Multiple evolutionary mechanisms contribute to the complex patterns of sequence polymorphism in primate HLA class II genes.
• The findings provide insights into the generation and maintenance of immune system diversity.