ABSTRACT
Abstract ..................................................................................................... 2 1.1 Introduction ...................................................................................... 2 1.2 Recombining Antigen Receptors in Jawless Vertebrates ................. 3 1.2.1 Immune-Related Genes in Lamprey Lymphocyte-Like
Cells ..................................................................................... 3 1.2.2 Identification of Recombining Variable Lymphocyte
Receptor (VLR) Genes ........................................................ 4 1.2.3 Recombining VLR Genes: Generation of Repertoire
Diversity ............................................................................... 6 1.3 Structural Characteristics of VLR Antibodies ................................. 8 1.4 Lymphoid Cell Lineages in the Sea Lamprey ................................ 10 1.4.1 VLR Surface Expression Characterizes Distinct
Lineages of Lamprey Lymphocytes ................................... 10 1.4.2 Developmental Origins of Lamprey Lymphocytes ............ 12 1.5 Conclusions .................................................................................... 13 Keywords ................................................................................................ 14 References ............................................................................................... 14
ABSTRACT
The ability of organisms to respond to pathogenic challenge with a highly specific immune response was considered, until recently, to have emerged after the divergence of jawed from jawless vertebrates. It has now become clear that jawless vertebrates developed an adaptive immune system with an antigen receptor repertoire that rivals that of jawed vertebrates in magnitude. Investigations of the jawless vertebrate adaptive immune system have revealed an unexpected example of convergent evolution in which antigen receptors with fundamental structural differences when compared to the immunoglobulin-based recombining antigen receptors of jawed vertebrates fulfill similar functions. Despite the use of distinct receptor architecture, the basic operating principles of adaptive immunity, including somatic receptor diversification and differentiation into humoral and cellular lineages, are remarkably conserved between jawed and jawless vertebrates over a large evolutionary distance.
