Immunosuppressive mechanisms during viral infectious diseases.

For a virus to establish persistence in the host, it has to exploit the host immune system such that the active T-cell responses against the virus are curbed. On the other hand, the goal of the immune system is to clear the virus, following which the immune responses need to be downregulated, by a process known as immunoregulation. There are multiple known immunoregulatory mechanisms that appear to play a role in persistent viral infections. In the recent past, IL-10 and PD-1 have been identified to be playing a significant role in the regulation of antiviral immune responses. The evidence that viruses can escape immunologic attack by taking advantage of the host's immune system is found in LCMV infection of mice and in humans persistently infected with HIV and HCV. The recent observation that the functionally inactive T-cells during chronic viral infections can be made to regain their cytokine secretion and cytolytic abilities is very encouraging. Thus, it would be likely that neutralization negative immune regulation during persistent viral infection would result in the preservation of effector T-cell responses against the virus, thereby resulting in the elimination of the persistent infection.