Variable lymphocyte receptor

Jawless vertebrates, which today consist entirely of lampreys and hagfish (the Cyclostomi), have an adaptive immune system similar to that found in jawed vertebrates. The lymphocytes of the cyclostomian AIS have roles roughly equivalent to those of B-cells and T-cells, but instead of variable immunoglobulins and T-cell receptors they use variable lymphocyte receptors to generate the diversity required for an adaptive immune system.