ABSTRACT
Introduction Protective immunity in all vertebrates is mediated by both innate and adaptive immune systems (AIS). Innate immune systems are also found in invertebrates, whereas a lymphocyte-based AIS only exists in the vertebrates (Figure 8.1). As the rst line of host defense, the innate immune system is mediated by phagocytic cells, such as dendritic cells and macrophages, that typically employ a limited number of germline-encoded pattern-recognition receptors, including Toll-like receptors, retinoic acidinducible gene I-like receptors, and nucleotide-binding oligomerization domain-like receptors, to sense conserved pathogen-associated molecular patterns expressed by microbial pathogens (Kawai and Akira, 2009). Innate
Introduction .................................................................................................... 207 Early studies of the hagsh adaptive immune response ......................... 209
Humoral response ..................................................................................... 209 Cellular response ....................................................................................... 210 Lymphoid tissues ...................................................................................... 210
Discovery of VLRs ..........................................................................................211 Hagsh VLR genes: Structure and comparison with lamprey VLR genes ........................................................................................................ 213 Hagsh VLR assembly mechanism and sequence diversity ................... 213 Structure of the VLR antigen-binding domain .......................................... 217 Hagsh VLR expression in B-and T-like lymphocyte lineages .............. 219 Functional potential of the agnathan AIS ................................................... 220 Conclusion ...................................................................................................... 221 Acknowledgments ......................................................................................... 222 References ....................................................................................................... 222
immunity is an ancient defense strategy that both invertebrate and vertebrate species use to protect against infection by potential pathogens in a relatively nonspecic manner. In contrast, both jawed and jawless vertebrates have an AIS that serves as a second line of defense by employing a vast repertoire of anticipatory receptors on lymphocytes to recognize specic antigens. A distinguishing feature of the AIS is the capacity for memory of previous antigen encounters, which allows for a more rapid response to a previously encountered pathogen (Dunn-Walters and Ademokun, 2010).
