This is what I got back and it kind of makes sense to me.

Harry
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There is difference between cellular immune response and humoral immune response. Cellular immune response, also referred to as a Th1 response, is a cell mediated response indicative of inflammation and cell destruction. Which is what Tysabri increased. The humoral response, which the article states remained unchanged, is a Th2 response in which the immune cells produce antibodies to viruses to destroy and prevent further and future infection in the body by the viruses. The article states that the humoral response was unchanged yet the cellular immune response was increased. This indicates that the virus is proliferating and causing cell destruction and the immune system isn't fighting back by producing antibodies. Thus, this is a silent destruction going on and the reason that they say there is no evidence of reactivation is because the body isn't launching an attack. This attack would normally produce the outward symptoms and reactivation is often measured by the number of antibodies being produced by the body.

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