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. Author manuscript; available in PMC: 2016 Jul 1.
Published in final edited form as: Cell Immunol. 2015 May 1;296(1):87–94. doi: 10.1016/j.cellimm.2015.04.007

Figure 1.

Figure 1

Evolution of alternative adaptive immune systems in jawless and jawed vertebrates (modified from [89]). The LRR-based VLR genes are found only in the jawless vertebrates, whereas Ig-based BCR, TCR and MHCI/II genes are limited to the extant jawed vertebrates. Neither of these types of antigen recognition receptors has been found in amphioxus and tunicates, suggesting that the LRR-based VLRs and the Ig-based BCRs and TCRs emerged through convergent evolution. The presence of one and the other of these lymphocyte-based adaptive immune systems attests to their survival advantage.