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Abstract: "The adaptive immune system (AIS) in mammals, which is centred on lymphocytes bearing antigen receptors that are generated by somatic recombination, arose approximately 500 million years ago in jawed fish. This intricate defence system consists of many molecules, mechanisms and tissues that are not present in jawless vertebrates." P.53 right column top paragraph: "With some exceptions, and despite the involvement of the well conserved and rapidly evolving molecular features described above, the AIS of jawed vertebrates has been remarkably uniform over 500 million years. Functional assays of jawless vertebrates (lampreys and hagfish) have shown signs of adaptive immunity, but neither adaptive immune molecular characteristics nor tissues, such as a thymus or spleen, were detected in these animals." |