Some of the virions that enter the respiratory pathway become stuck to the mucous lining of the pathway. They are then pushed to the larynx by the cilia that line the pathway. They end up being swallowed and destroyed by stomach acid.
The particles that survive the mucousal defense stimulate an antibody response. Antibodies respond to the HA and NA glycoproteins. That is why changes to the H and N regions are so dangerous to human populations. Some of the antibodies are in the mucous, but the vast majority are in the blood. In addition to antibodies, a cellular immune response of macrophages, natural killer cells, interferon y , interleukin-2, CD4 and CD8 cells is stimulated. However, the CD4 cells cause inflammation that makes the possible pneumonia much more morbid and even fatal.
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