Adaptive immunity in jawless fish

Jawless vertebrates, which today consist entirely of lampreys and hagfish, have an adaptive immune system similar to that found in jawed vertebrates. The cells of the agnathan AIS have roles roughly equivalent to those of B-cells and T-cells, with three lymphocyte lineages identified so far:

• VLRA (most similar to α/β T cells, in its role and pathway of differentiation)
• VLRB (most similar to B cells)
• VLRC (most similar to γ/δ T cells)

VLRA and VLRB were identified in 2009, while VLRC was discovered in 2013. Instead of immunoglobulins, they use variable lymphocyte receptors.