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Researchers Trace Origin of Key Cell of Immune System

News Release

Jennifer Martin, CSREES Staff, (202) 720-8188

WASHINGTON, Oct. 2, 2006 – Funding from the U.S. Department of Agriculture and the National Science Foundation has enabled University of Pennsylvania researchers to link key cells in fish and frogs to new immune system functions that could lead to more effective vaccines for commercial fish farming.

“These novel research findings have implications for the commercial fish farming industry,” said Dr. Gale Buchanan, USDA under secretary for Research, Education and Economics. “More effective vaccines will make the profession more profitable and environmentally sound.”

The study found that B lymphocytes (B cells) of fish and frogs are very effective at ingesting and eliminating foreign particles and microbes, a process called phagocytosis. B cells, while essential to immune responses by generating antibodies, have not been known perform phagocytosis. Rather, it was thought that this capability belonged to specialized cells called macrophages.

Many of the current vaccines given to farmed fish don’t take into account the capacity of B cells to pick up large particles. This discovery is likely to foster research on new fish vaccines that target and/or stimulate B cells to respond to the delivered immunogen, thereby making the vaccines more effective.

J. Oriol Sunyer and his colleagues at the University of Pennsylvania’s School of Veterinary Medicine found the previously unsuspected B cell activity while examining the immune cells of rainbow trout. They determined that B cells accounted for more than 60 percent of phagocytes in the blood of these fish.

Sunyer’s findings support the idea that B cells evolved from an ancestral phagocytic cell type and provide the basis for understanding the close developmental link between B lymphocytes and macrophages in mammals. The findings are not only important for understanding the evolution and function of immune cells in fish, but also may point to novel roles of B cells in mammals.

Sunyer believes there was a transitional period of B cell evolution during which phagocytosis remained in fish, but disappeared in mammals. This discovery opens up the possibility that small populations of phagocytic B cells still remain in mammals playing a critical role in their immune defense systems.

The October issue of Nature Immunology, a leading journal in the field of immunology, features the study as its cover story.

Sunyer received funding from the USDA’s Cooperative State Research, Education and Extension Service through the National Research Initiative. Additional funding was provided by the National Science Foundation.

CSREES advances knowledge for agriculture, the environment, human health and well-being, and communities by supporting research, education, and extension programs in the Land-Grant University System and other partner organizations. For more information, visit http://www.csrees.usda.gov.