Inflammation Key to Severity of Avian Flu

The deadly H5N1 strain of avian flu triggers levels of inflammatory proteins that are more than 10 times higher than the common flu virus H1N1. These are likely to result in an uncontrolled inflammatory response that can escalate into life-threatening pneumonia and acute respiratory distress.

To investigate why this strain is so deadly to humans, researchers from the University of Hong Kong and collaborators in Vietnam studied the levels of a subset of the pro-inflammatory proteins, or cytokines and chemokines, induced by the H5N1 virus in human lung cells. They compared these protein levels with levels induced by the human flu virus H1N1.

The results showed that H5N1 is a much more potent inducer of pro-inflammatory proteins than H1N1. One day after infection with H5N1, the levels of the chemokine IP-10 in bronchial epithelial cells reached 2,200 pg/ml, compared to cells infected with H1N1, which reached only 200 pg/ml. The findings were reported in the November 11, 2005, online edition of Respiratory Research (www.biomedcentral.com).

Michael Chan and colleagues from the University of Hong Kong conducted the research. They pointed out that chemokines and cytokines are "messengers of the immune system” and are critical in coordinating and regulating the immune response. Altering this balance is apt to lead to an uncontrolled inflammatory response in the lung, which probably explains in part the severe lung inflammation associated with avian flu virus H5N1.




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