We also evaluated the expression of genes representative of the
adaptive immune response, immunoglobulins (Ig) M and T, and the
Th cell markers CD4 and CD8. In mammals, Igs can be divided into
five categories and for a long time, it was believed that only one of
them, IgM, existed in fish. However several other functional Igs have
recently been discovered in teleost fish and Ig genes were identified
in rainbowtrout, named IgT, similar to zebra fish IgZ [50].