How Viruses Escape the Immune Responses; Inhibitory Proteins; Antigenic drift and antigenic shift

Viral Immuno-Evasion ways;
1. By Inhibitory Proteins e.g.
Hepatitis C virus overcomes the antiviral effect of the interferons by blocking protein Kinase R.
HSV-1 and HSV-2 express protein that inhibit antigen processing and inhibits presentation of viral antigen to CD8+ T cells.
Adenoviruses and cytomegalovirus (CMV) reduce the surface expression of class I MHC molecules and inhibit antigen presentation to CD8+ T cells.
CMV, measles virus, and HIV reduce levels of class II MHC molecules on the cell surface.

2. By Inhibition of Complements Components e.g.
Vaccinia virus secretes a protein that binds to the C4b complement component, inhibiting the classical complement pathway.
Herpes simplex viruses have a glycoprotein component that binds to the C3b complement component, inhibiting both the classical and alternative pathways.

3. By Immunosuppression e.g.
A large number of viruses evade the immune response by causing generalized immunosuppression. e.g. paramyxoviruses, Epstein-Barr virus (EBV), cytomegalovirus, and HIV. Some viruses suppress immune responses by infecting lymphocytes or macrophages. EBV produces a protein similar to IL-10; like IL-10 that suppresses cytokine production by the TH1 subset, resulting in decreased levels of IL-2, TNF, and IFN.

4. Antigenic drift and antigenic shift
Antigenic variation results in emergence of new infectious strains e.g. influenza virus antigenic shift results in emergence of a new subtype of influenza.