Physicians may someday get an extra tool to deal with a global outbreak of bird flu in humans. In laboratory experiments, antibodies from patients who successfully battled avian influenza protected mice from the virus, researchers say in a paper published in this month's issue of Public Library of Science (PloS) Medicine. Although less practical than antiviral drugs, antibodies could provide crucial help, says Albert Osterhaus, a virologist at Erasmus Medical Center in Rotterdam, the Netherlands. Industrially produced antibodies are already used against a variety of diseases, including rabies and hepatitis A and B. But they may be useful in influenza as well. During the 1918 influenza pandemic, some doctors experimentally treated patients by transfusing them with blood products from recovered patients; a review study published last year suggested that such treatments may have cut mortality in half. For the new study, researchers at the Hospital for Tropical Diseases in Ho Chi Minh City, Vietnam, took blood samples from four patients as they recovered from infection with H5N1--the virus that causes avian influenza--in 2004 and 2005. Scientists at the Institute for Research in Biomedicine (IRB) in Bellinzona, Switzerland, then isolated the so-called memory B cells, which produce antibodies; using a special trick that employs the Epstein-Barr virus, they "immortalized" these cells to make them crank out antibodies indefinitely. Finally, researchers at the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, tested four of these antibodies in a mouse strain highly susceptible to H5N1 infection.