B. Bajoghli et al., “A thymus candidate in lampreys,” Nature, 470:90-94, 2011. Free F1000 evaluation
Jawless vertebrates such as lampreys and hagfish have an adaptive immune system, with two lymphocyte cell types that resemble T and B cells, despite lacking other hallmarks of adaptive immunity, such as immunoglobulins and MHC. Now, Thomas Boehm at the Max Planck Institute in Freiburg and colleagues, think they have identified a new component of the adaptive immune system: the lamprey thymus.
The lack of a thymus in lampreys was puzzling, as the organ is essential for the final step of T-cell maturation in humans. Do human and lamprey immune systems share a common ancestor, or was the evolution convergent—hitting on a similar solution by chance? Unlike B cells, “T cells are always linked to a thymus,” says Bruno Kyewski of the German Cancer...
After Max Cooper at Emory University in Atlanta showed lampreys had T-like cells, Boehm’s group discovered the expression of a lamprey equivalent of FOXN1—a transcription factor required for the proper development of a thymus. Boehm and Cooper worked together to show that the lamprey T-like cells, but not the B-like cells, were processed in the same place where FOXN1 is expressed—the lamprey’s gill basket—as would be expected if it were a genuine thymus.
The MHC question
MHC molecules, which interact with T-cell receptors to initiate an immune response, are “the hallmark of the cellular immune system,” says Boehm. Searching for the lamprey MHC molecules is next on Boehm’s plate.