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University of California, Davis, researchers studying the 2009 H1N1 influenza virus, formerly referred to as “swine flu,” have identified a group of immunologically important sites on the virus that are also present in seasonal flu viruses that have been circulating for years.
These molecular sites appear to result in some level of immunity to the new virus in people who were exposed to the earlier influenza viruses. More than a dozen structural sites, or epitopes, in the virus may explain why many people over the age of 60, who were likely exposed to similar viruses earlier in life, carry antibodies or other type of immunity against the new virus, immune responses that could be attributed to earlier flu exposure and vaccinations. [..] “These findings indicate that human populations may have some level of existing immunity to the pandemic H1N1 influenza and may explain why the 2009 H1N1-related symptoms have been generally mild,” Cardona said. “Our hypothesis, based on the application of data collected by other researchers, suggests that cell-mediated immunity, as opposed to antibody-mediated immunity, may play a key role in lowering the disease-causing ability, or pathogenicity, of the 2009 H1N1 influenza,” Xing added. He noted that immune responses based on production of specific cells, known as cytotoxic T-cells, have been largely neglected in evaluating the efficacy of flu vaccinations. In this type of immune response, the T-cells and the antiviral chemicals that they secrete attack the invading viruses. [..] Further study, however, revealed that the virus actually included genes from viruses found in birds and humans, as well as pigs. At first, this H1N1 influenza virus apparently caused a high number of deaths among patients in Mexico and among people with certain pre-existing medical conditions. But as it has progressed to become a pandemic or geographically widespread virus, H1N1 has caused relatively mild symptoms and few deaths. [..] The UC Davis research To probe this phenomenon, the UC Davis researchers surveyed data from earlier studies of epitopes known to exist on different strains of seasonal influenza A. They found that these epitopes, present in other seasonal H1N1 influenza strains around the world and capable of triggering an immune response, were also present in the strains of H1N1 2009 that were found in California, Texas and New York. Interestingly, although previous H1N1 viruses seem to have produced a protective antibody response in exposed people, these antibodies largely did not provide cross-protection for individuals infected with the H1N1 2009 strain of influenza. The researchers theorize that, rather than stimulating protective antibodies, the epitopes of the new H1N1 2009 virus produced an immune response by triggering production of cytotoxic T-cells, which boost a person’s immune defenses by killing infected cells and attacking the invading viruses. [..]