You've got more in common with a primitive blood-sucker than you thought. According to immunologists, lampreys have immune system cells that are surprisingly similar to the infection-fighting white blood cells in our own immune systems. This discovery could help explain how immune systems evolved.
Jawless vertebrates such as the lamprey represent a dividing line in immune system evolution. All other vertebrates have adaptive immune systems, which selectively attack foreign agents and retain a "memory" of their molecular flags, or antigens. If attacked again by an invader bearing the same antigen, the immune system uses that molecular memory to launch a more effective defense. Such an advanced defense system couldn't have evolved overnight, however, so researchers look to lampreys for clues that might explain its evolution. Think of it as immunology's version of the "search for the missing link."
The link just got tighter. By studying juvenile lamprey intestinal cells, immunologists Max Cooper of the University of Alabama, Birmingham, and Jan Klein of the Max Planck Institute in Tübingen, Germany, discovered cells that look just like mammalian lymphocytes, the white blood cells that battle invaders. Surprisingly, lamprey lymphocytes express many of the same genes that mammalian lymphocytes use to call the immune system into action. But as the team reports online 4 October in the Proceedings of the National Academy of Sciences, the lamprey cells lack the genes for critical docking stations on the lymphocyte cell surface that enable the immune system to distinguish and remember different foreign cells. The authors suggest that lampreys are poised at the brink of evolving an adaptive immune system.
The big question now is why would so much of the molecular machinery for an adaptive immune system be present in lampreys if it wasn't functioning for that purpose, says evolutionary biologist Rustom Antia of Emory University in Atlanta, Georgia. "This research sets the stage to ask some exciting new questions about immune system function," he says.