Interferons (IFN) are glycoproteins that, among other products, are released from virus-infected cells. In neighboring cells, interferon stimulates the production of "antiviral proteins." These inhibit the synthesis of viral proteins by (preferential) destruction of viral DNA or by suppressing its translation. Interferons are not directed against a specific virus, but have a broad spectrum of antiviral action that is, however, species-specific. Thus, interferon for use in humans must be obtained from cells of human origin, such as leukocytes (IFN-a), fibroblasts (IFN-P), or lymphocytes (IFN-y). Interferons are also used to treat certain malignancies and autoimmune disorders (e.g., IFN-a for chronic hepatitis C and hairy cell leukemia; IFN-p for severe herpes virus infections and multiple sclerosis).
Virustatic antimetabolites are "false" DNA building blocks (B) or nucle-osides. A nucleoside (e.g., thymidine) consists of a nucleobase (e.g., thymine) and the sugar deoxyribose. In antime-tabolites, one of the components is defective. In the body, the abnormal nucle-osides undergo bioactivation by attachment of three phosphate residues (p. 287).
Idoxuridine and congeners are incorporated into DNA with deleterious results. This also applies to the synthesis of human DNA. Therefore, idoxuridine and analogues are suitable only for topical use (e.g., in herpes simplex keratitis).
Vidarabine inhibits virally induced DNA polymerase more strongly than it does the endogenous enzyme. Its use is now limited to topical treatment of severe herpes simplex infection. Before the introduction of the better tolerated acyclovir, vidarabine played a major part in the treatment of herpes simplex encephalitis.
Among virustatic antimetabolites, acyclovir (A) has both specificity of the highest degree and optimal tolerability,
Glycoprotein Interferon r
Proteins with antigenic properties
Specific immune defense e.g., cytotoxic T-lymphocytes
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