Biological basis for the clinical use of interferon.

Interferons are proteins produced by certain cells in response to stimuli such as foreign cells (including tumour cells), bacteria, and viral antigens. They interact both with the interferon producing cells and other cells through production of effector proteins. There are three main types of interferons, known as alpha, beta, and gamma, which have direct antiviral and immunomodulatory effects. Antiviral effects may include inhibition of viral replication, protein synthesis, maturation, or release from infected cells. Immunomodulating effects may include enhancement of macrophage, cytotoxic T cell, and natural killer cell activity. In chronic viral hepatitis, the precise mechanisms of action of alpha interferon are not yet certain. Patients with chronic hepatitis B, however, have been shown to lack endogenous interferon production; those who respond to alpha interferon treatment show a characteristic peak in serum amino-transferase activity before resolution of the infection, indicating an immune reaction. In chronic hepatitis C, the antiviral effect may be more important; patients who respond to alpha interferon tend to have higher values of 2'5' oligo adenylate synthetase, an enzyme induced by interferons that breaks down viral RNA. The clinical relevance of anti-interferon neutralising antibodies produced by some patients during interferon treatment has yet to be firmly established.