The researchers produced antibodies with cells isolated from these survivors and demonstrated the immunity against the highly lethal 1918 flu virus in mice.

The finding suggests that the antibodies can be used as an effective treatment for another virus similar to the 1918 flu breaks out in the future.

The 1918 flu pandemic worldwide killed an estimated 50 million people.   Health officials worldwide worry that a similar flu pandemic may strike some time in the future, potentially killing millions of people.

The study titled "Neutralizing antibodies derived from the B cells of 1918 influenza pandemic survivors," was published in the advanced online edition of the journal Nature.

"Ninety years after survivors encountered the 1918 pandemic influenza virus, we collected antibody-producing B cells from them, and successfully isolated B cells that produce antibodies that block the viral infection," said contributing author Dr. Christopher Basler, PhD, Associate Professor of Microbiology at Mount Sinai School of Medicine.

"The antibodies produced by these cells demonstrated remarkable power to block 1918 flu virus infection in mice, proving that, even nine decades after infection with this virus, survivors retain protection from it."

"The fact that you can isolate these anti-1918 memory B cells so long after infection will hopefully provide the impetus to further study the mechanisms behind long lived immunity," said Dr. Osvaldo Martinez, post-doctoral fellow at Mount Sinai School of Medicine.

For this study, Dr. Eric Altschuler at the University of Medicine and Dentistry of New Jersey recruited 32 individuals age 91-101 years and lived through the influenza pandemic to donate blood. Dr. Basler's lab tested the blood and found that antibodies recognize the 1918 virus.

Dr. James Crowe and colleagues at Vanderbilt University produced antibodies from these individuals' blood cells and Dr. Basler's lab demonstrated the potent neutralizing activity of the antibodies against 1918 virus.

The virus was resurrected in 2005 by researchers from Mount Sinai and the Armed Forces Institute of Pathology from the bodies of people killed in the outbreak and preserved in the permanently frozen soil of Alaska.

Antibodies were also provided to Dr. Terrence Tumpey at the Centers for Disease Control and Prevention to test in mice the potency of the antibodies derived from the 1918 survivors.

Crowe's lab isolated extremely rare B cells from eight samples to produce antibodies in culture and found seven were able to produce antibodies to a 1918 virus protein.

Then Crowe's team fused cells with the highest levels of activity against the virus with immortal cells to create cells that secrete monoclonal antibodies to the 1918 flu virus.

The antibodies thus made reacted strongly to the 1918 virus and cross-reacted with proteins from the related 1930 swine flu virus, but not more modern flu strains.

Crowe in collaboration with the CDC tested the immunity of these antibodies in mice and found those who received the low doses died while those who received high doses all survived after exposure to the 1918 flu virus.

Although aging typically causes immunity to weaken, "these are some of the most potent antibodies ever isolated against a virus," Crowe said. "They're the best antibodies I've ever seen."

"Our findings show that survivors of the pandemic have highly effective, virus neutralizing antibodies to this powerful virus, and humans can sustain circulating B memory cells to viruses for up to 9 decades after exposure," said Dr. Tshidi Tsibane, post-doctoral fellow at Mount Sinai School of Medicine. "These findings could serve as potential therapy for another 1918-like virus."