Viejos anticuerpos contra la influenza estacional apuntan contra el virus de la influenza porcina

Los resultados de laboratorio explican por qué los pacientes jóvenes son golpeados más fuertemente por la presente cepa H1N1
Los anticuerpos contra algunas cepas de la influenza estacional de años anteriores, pueden resultar activos contra la influenza porcina H1N1 que circula actualmente en el mundo, según reporta un reciente estudio. Los hallazgos sugieren una explicación del porqué la influenza porcina parece infectar a los jóvenes con más frecuencia que a los adultos mayores quienes son, usualmente, más susceptibles al los virus de la influenza estacional.
Solamente el 1% de los casos de fiebre porcina en los Estados Unidos aparecen en personas de más de 65 años. CDC
El estudio, que fue publicado en el Morbidity and Mortality Weekly Report, analizó muestras de sangre tomadas de 359 participantes de los estudios vacunales para la influenza conducidos desde 2005 hasta 2009. El 33% de las muestras de los individuos de más de 60 años tenían anticuerpos que reaccionaban contra el virus de la fiebre porcina, comparados con el 6% al 9% de las muestras de personas entre 18 y 64 años y con ninguna de las muestras tomadas a niños 1.
Fuente: Ledford, H., 2009. Old seasonal flu antibodies target swine flu virus : Nature News. Nature. Disponible en: http://www.nature.com/news/2009/090521/full/news.2009.503.html [Accedido Mayo 25, 2009]

The results match the apparent current epidemiology of swine flu infection, says Anne Schuchat, interim deputy director for the Science and Public Health Program at the Centers for Disease Control and Prevention (CDC) in Atlanta. Most cases of swine flu have occurred in people who are under 60 years old, and only 1% of confirmed swine flu infections in the United States were in patients over the age of 65.
Nevertheless, the results should be interpreted with caution, Schuchat urged in a press briefing today. Researchers have shown that the antibodies react with the virus in test-tube assays, but they have not yet shown that the antibodies can fend off the virus in animals or people. “Whether this particular assay will pan out over time as predictive of clinical protection, we can’t say,” Schuchat said.
Cross-protection
For the study, CDC researchers used two tests to determine whether antibodies in the blood were active against the swine flu. One test studied the impact of the antibodies on growth of the virus in cell culture, and the other assayed the ability of the antibodies to inhibit an important viral protein called hemagglutinin.
The results indicated that vaccination against recent H1N1 seasonal flu viruses did not generate antibodies that react with the swine flu virus. But exposure to older seasonal flu viruses or vaccines — perhaps dating back to the 1950s or earlier — may have yielded cross-reactive antibodies in some older study participants.
Although the results have not yet been confirmed clinically, the researchers used standard techniques that are often used in preclinical studies of flu vaccines, says Ralph Tripp, a viral immunologist at the University of Georgia in Athens. “The reality is, there does appear to be a substantial level of cross-reactivity in those adults aged 60 years and older,” he says.
Genetic analysis of the new swine flu virus has shown that it differs dramatically from previous seasonal viruses. But Tripp notes that H1N1 viruses were circulating in swine during the 1940s and 1950s and could have mixed with seasonal flu viruses during that time. Exposure to these viruses could have launched an antibody response that continues to protect individuals against today’s swine flu.
Meanwhile, Schuchat notes that it is possible for immune responses to the current swine flu and past seasonal viruses to overlap, despite the genetic dissimilarity. “We don’t have a particular virus that we’re thinking about,” she says, “but we’re wondering if there might have been some viruses around in the ’30s, ’40s and ’50s that might be immunologically similar to the one we’re seeing now.”