Penn Researchers Investigate Evolutionary Link

PHILADELPHIA  -- 11/1/06 - Researchers from the University of  Pennsylvania School of Veterinary Medicine have discovered an evolutionary link between the immune systems of fish and mammals in the form of a primitive version of B cells - white blood cells of the immune system. Their studies link the evolution of the adaptive immune system in mammals,  where B cells produce antibodies to fight infection, to the more primitive  innate immunity in fish where they found that B cells take part in  phagocytosis (cell eating).

The finding, which appears in the online version of Nature Immunology, was featured on the cover of the October issue and offers a potential new strategy for developing much-needed fish vaccines.

"When examining fish B cells we see them actively attacking and eating  foreign bodies, which is a behavior that, according to the current dogma, just  shouldn't happen in B cells," says J. Oriol Sunyer, a professor in Penn Vet's  Department of Pathobiology.  "I believe it is evidence for a very real  connection between the most primitive forms of immunological defense, which  has survived in fish, and the more advanced, adaptive immune response seen in  humans and other mammals."

About 400 million years ago, the earliest ancestors of modern fish split  off of the evolutionary pathway that became the earliest ancestors of modern  mammals, the university reports. In modern mammals, the B cell is a highly adapted part of the  immune system chiefly responsible for, among other things, the creation of  antibodies that tag foreign particles and microbes for destruction. Mammals have phagocytic cells, but they are a specialized few cells identified apart from the complex interactions that drive other white blood  cells.

Sunyer and his colleagues discovered this previously unsuspected B-cell  activity while examining the immune cells of rainbow trout and catfish. The researchers determined that these attack B cells account for more  than 30 percent to 40 percent of all immune cells in fish, while phagocytic cells only make up a  small portion of the total number of immune cells in mammals. Further  research also showed that a significant portion of amphibian B cells retained  their digestive traits.     

According  to Sunyer, Penn's findings are not only important for understanding the  evolution and function of immune cells in fish but also may point out to novel  roles of B cells in mammals.

Funding for this research was provided by the National Science Foundation  and United States Department of Agriculture.