Some viruses are able to escape the immune responses generated against them and to establish a latent state that is not visible to the immune system. Such viruses hide in CD4+ T cells, all T cells, B lymphocytes, germinal epithelial cells, neurons and others. They can reactivate at times when the immunity is compromised. It is not known what are the effects, if any, of dormant viruses on the immune system. Some of these viruses contribute to malignant transformation of cells. Recent studies have implicated that presence of latent viruses such as CMV might be driving the T cells to terminal differentiation and exhaustion. Retroviruses incorporate into the human genome and now represent as much as 8% of it constituting of about 30 000 different retroviruses. In addition, various other transposable elements like these make up to 45% of the human genome. Other latent viruses such as Bornavirus are believed to be involved in the pathogenesis of human psychiatric diseases such as bipolar disorder and depression. Attempts to design vaccines that will prevent the virus from going into latency have been scarce.
Keywords: Immune evasion, latent infection, persistent infection, dormant, reactivation, CD4+T cell, HIV, HHV-6, HHV-7, CMV, HTLV-1, HTLV-2, HSV, VZV, EBV, JC, VK, measles, immunosenesence, terminally differentiated, endogenous retroviruses, retrotransposons, prokaryotic retrons, “retrotranscripts”, CMV, Bornavirus