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""We looked at the molecular markers for seasonal influenza viruses dating back 20 years and compared them with the molecular markers of the H1N1 influenza virus," said Bjoern Peters, Ph.D., lead author on the study published today in the Proceedings of the National Academy of Sciences. "We found that the immune system's T cells can recognize a significant percent of the markers in swine flu." T cells are infection-fighting white blood cells in the body's immune system. "Nobody knows what level of immunity is sufficient for protection. We do know that a T cell response is not enough to prevent being infected by the virus. But, if infected, our data suggests that T cells in those who have previously been exposed to influenza may make the infection less severe," Dr. Peters said.
The findings are based on knowledge that the body's T cells recognize and will launch an attack against viruses -- in this case certain molecular pieces of the swine flu -- that they have seen before.
The research team also looked at the immune system's antibody-producing B cell response to the H1N1 virus. In this area, they saw only 17 percent recognition of the markers on the H1N1 as compared to seasonal flu. B cells, and their ability to produce antibodies that remember a virus, are the basis for vaccines to protect against subsequent infections by similar viruses. "Since the antibody recognition of the H1N1 virus was relatively low as compared to previous flu viruses, it means that the vaccine is important to prevent being infected by the H1N1 virus," said Dr. Peters.
In a study available online and appearing in a future issue of Proceedings of the National Academy of Sciences, a UT Southwestern Medical Center researcher and his collaborators in California show that the molecular makeup of the current H1N1 flu strain is strikingly different from previous H1N1 strains as well as the normal seasonal flu, especially in structural parts of the virus normally recognized by the immune system.
Prior research has shown that an individual's immune system is triggered to fight off pathogens such as influenza when specific components of the immune system - namely antibodies, B-cells and T cells - recognize parts of a virus known as epitopes. An individual's ability to recognize those epitopes - spurred by past infections or vaccinations - helps prevent future infections. The challenge is that these epitopes vary among flu strains.
"We hypothesize that older people are somewhat protected because the epitopes present in flu strains before 1957 may be similar to those found in the current H1N1 strain, or at least similar enough that the immune system of the previously infected person recognizes the pathogen and knows to attack," said Dr. Richard Scheuermann, professor of pathology and clinical sciences at UT Southwestern and a co-author of the paper. "Those born more recently have virtually no pre-existing immunity to this pandemic H1N1 strain because they have never been exposed to anything like it."
The above WHO comments from the latest update on sequences from isolates from Ukraine (see map) raised additional concerns. Earlier comments indicated that there were no "large changes", which simply meant that there was no significant reassortment with other influenza viruses, such as seasonal flu, and the constellation of genes was unchanged (5 swine, 1 human, and 2 avian).
However, the comments did not rule out small changes, such as receptor binding domain changes seen in other swine H1N1 isolates such as D225E, D225N, and D225G. The latter two changes were of concern because they had recently been isolated from Sao Paulo fatal cases, and three of the four isolates with D225N or D225G were found in lung samples, which were of conern because of reports of total destruction of lungs in Ukraine..
The recent comments from WHO stating that sequences are "similar" to other sequences does not rule out receptor binding domain changes, and such changes were not denied, as was done previously with H5N1 sequences from patients in Pakistan, which again raises concerns that the sequences from Ukraine do have receptor binding domain changes.
Such changes could affect transmission or tropism and could also affect the vaccine reactivity. The involvement of the CDC in Atlanta, as well as Mill Hill in London suggests the isolates were tested against the current vaccine, which would again suggest that there were sequence differences, but that the differences did not significantly reduce titers against reference anti-sera.
A 2003 report in the Journal of Experimental Medicine published by researchers at Imperial College London demonstrates the possibility of preventing a cytokine storm by inhibiting or disabling T-cell response. A few days after T cells are activated, they produce a biologic molecule called OX40, a "survival signal" that keeps activated T-cells working at the site of inflammation during infection with influenza or other pathogens. OX40 binds to receptors on T-cells, preventing them from dying and subsequently increasing cytokine production. A combined protein, OX40-immunoglobulin (OX40-Ig), a human-made fusion protein, prevents OX40 from reaching the T-cell receptors, thus reducing the T-cell response. Experiments in mice have demonstrated that OX40-Ig can reduce the symptoms associated with an immune overreaction while allowing the immune system to fight off the virus successfully. By blocking the OX40 receptor on T-cells, researchers were able to prevent the development of the most serious flu symptoms in these experimental mice and reported the results in New Scientist. The drug, to be made by a company called Xenova Research (Xenova Research was purchased by Celtic Pharma, a private equity firm, in September 2005), was supposed to be in phase I clinical trial in 2004, but its status is currently unknown.
In addition, preliminary data has shown that simvastatin induced down-regulation of OX40 and OX40L mRNA and protein in a concentration-dependent manner, and antagonized the interferon-gamma-induced increase in OX40 and OX40L mRNA and protein levels. Further, serum levels of soluble OX40L and matrix metalloproteinase 9 levels were significantly reduced in patients with atherosclerotic cerebral infarction who were treated for 6 months with routine therapy plus simvastatin (n = 46) compared with patients receiving routine therapy alone (n = 30).
There are fears that H1N1 has now mutated and resembles the Spanish flu virus that killed more than 50 million people at the beginning of the 20th century. Ukrainian doctors say the victims lungs are as black as charcoal. This prompts fresh concern that the swine flu virus has taken a deadly new form