Human interferon omega--a review.

A single functional gene in the human genome codes for interferon omega (IFN-omega), a monomeric glycoprotein distantly related in structure to IFN-alpha and IFN-beta, but unrelated to IFN-gamma. IFN-omega is secreted by virus-infected leukocytes as a major component of human leukocyte interferon. The human class I IFN receptor complex which mediates the biological activity of IFN-alpha and IFN-beta also binds IFN-omega. Its specific activity in a standard in vitro antiviral assay system is 4 x 10(8) U mg-1; potent antiviral activity against several DNA and RNA viruses has been demonstrated. IFN-omega inhibits proliferation of a variety of tumor cell lines in vitro. The protein stimulates natural killer cell activity, enhances expression of major histocompatibility complex class I (but not class II) antigens and inhibits proliferation of lymphocytes stimulated with mitogens or allogeneic cells. IFN-omega is unrelated to IFN-alpha, -beta and -gamma in its antigenic properties, as it does not cross-react with antisera or monoclonal antibodies in immunoassays or antiviral neutralization bioassays. Antibodies induced in patients by long-term IFN-alpha 2 therapy that block IFN-alpha 2 activity do not inactivate IFN-omega. As IFN-omega, like other human IFNs, has a species-restricted biological activity, evaluation of its therapeutic potential will have to await clinical trials.