Recent studies indicate that exposure to new flu strains stimulates antibody production towards older strains of the virus. This information suggests that researchers can make a longer-lasting influenza vaccine that has broader anti-flu properties. Researchers had some idea prior that the immune system could make use of its previous experience to make antibodies against future viruses. Prior to this study, there was no evidence to support this according to Patrick Wilson, an immunologist at the University of Chicago.
Peter Palese (Icahn School of Medicine at Mount Sinai, New York City) and colleagues studied 40 individuals in the Framingham Heart Study. They measured antibodies in blood samples from individuals born between 1917 and 1952 who had lived through flu pandemics that occurred in 1957, 1968 and 1977. Blood samples were taken at five-year intervals between 1987 and 2008. The group of researchers collected data on three pandemic flu strains and how antibodies against these strains over time. They were also able to collect information on the amount of antibodies against viruses that had mutated (altered versions of the same virus) that existed in 1981 and 1991.
They report that antibody levels against pandemic strains increased as these individuals came in contact with different strains of these flu viruses. They also found that the level of antibodies against an unchanged virus (cytomegalovirus) didn’t change. This suggested to the researchers that a new virus (mutated virus) was necessary for increasing production of old antibodies.
Dr. Ning Jenny Jiang, a bioengineer at the University of Texas at Austin, notes that the immune system tends to maintain old antibodies. Older individuals don’t have room in their “immunological attics” to support new antibodies.
This new study brings to light which parts of the flu virus activate the immune system into making antibodies with high affinity. Antibodies that are capable of binding to a wide range of viruses are those that can bind to the protein stalk part of the hemagglutinin protein in the surface of the viral coat. This is important because this protein stalk is what binds to host cells and the presence of an antibody prevents this and also marks the virus for destruction. It is known that the protein stalk changes little from year to year or flu virus to flu virus. This makes the stalk a vaccine candidate. However, the stalk doesn’t generally induce much in the way of antibody production. Palese believes the stalk can be combined with a wide range of viral heads such that a flu vaccine can be made to protect against a greater range of viruses. He also believes this kind of vaccine can last longer than the seasonal vaccines we currently have.
The study entitled “Neutralizing antibodies against previously encountered influenza virus strains increase over time: a longitudinal analysis” was published in Science Translation Medicine Vol. 5, August 14, 2013, p. 198ra107. doi: 10.1126/scitranslmed.3006637.
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