How does an influenza virus cause symptoms of the flu to spread in the human body

An Influenza virus cause symptoms via different mechanisms such as:

•the inhibition of adrenocorticotropic hormone (ACTH)

•production of the huge amounts of proinflammatory cytokines and chemokines  produced from influenza-infected cells

Influenza virus invades the cells when the cleavage of the viral hemagglutinin protein occurs by some of the human proteases. It is cleaved by proteases found in the throat and lungs (that is why these tissues are inflammatory).

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