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.
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.