2004/07/09 by John P. Cannon, Robert N. Haire, Jonathan P. Rast +1 · 145 citations
Immunology and Microbiology · Neuroscience · #Acquired immune system #Antibody #Aquaculture disease management and microbiota #B cell #Biology #Evolutionary biology #Gene #Gene family #Genetics #Genome #Immune system #Invertebrate Immune Response Mechanisms #Major histocompatibility complex #Neurobiology and Insect Physiology Research #Phylogenetic tree #Phylogenetics #Recombination #Recombination-activating gene #Somatic hypermutation #T cell #T-cell receptor #Vertebrate
paper · doi:10.1111/j.0105-2896.2004.00166.x
published in Immunological Reviews 200(1), 12-22 (Wiley)
openalex publication_date 2004/07/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/22
The adaptive immune system arose in ancestors of the jawed vertebrates approximately 500 million years ago. Homologs of immunoglobulins (Igs), T-cell antigen receptors (TCRs), major histocompatibility complex I (MHC I) and MHC II, and the recombination-activating genes (RAGs) have been identified in all extant classes of jawed vertebrates; however, no definitive homolog of any of these genes has been identified in jawless vertebrates or invertebrates. RAG-mediated recombination and associated junctional diversification of both Ig and TCR genes occurs in all jawed vertebrates. In the case of Igs, somatic variation is expanded further through class switching, gene conversion, and somatic hypermutation. Although the identity of the 'primordial' receptor that was interrupted by the recombination mechanism in jawed vertebrates may never be established, many different families of genes that exhibit predicted characteristics of such a receptor have been described both within and outside the jawed vertebrates. Recent data from various model systems point toward a continuum of immune receptor diversity, encompassing many different families of recognition molecules whose functions are integrated in an organism's response to pathogenic invasion. Various approaches, including both genomic and protein-functional analyses, currently are being applied in jawless vertebrates, protochordates, and other invertebrate deuterostome systems and may yield definitive evidence regarding the presence or absence of adaptive immune homologs in species lacking adaptive immune systems. Such studies have the potential for uncovering previously unknown mechanisms of generating receptor diversity.