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Unformatted text preview: used for identification, and they also enhance the pathogenicity of some viruses. For example, the virus that causes influenza has spikes that bind to red blood cells and cause them to clump together (hemagglutination). Nonenveloped viruses do not have the envelope. In these the capsid provides the protection for the nucleic acid and attaches to host cells. Whether the outer covering of a virus is an envelope or the capsid, it is this outer covering to which the immune system of the host responds by producing antibodies, which should be capable of binding to and inactivating the virus. Some viruses slip past this defense by frequently changing the characteristics of their outer covering to that the antibodies not longer recognize it. Influenzavirus is outstanding at this trick, and this is why flu shots have to change every year....
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- Fall '09