Interferons, serotonin and neurotoxicity

BACKGROUND: Interferons are a class of cytokines profoundly affecting immune function. Several interferons are now synthesized and used clinically, notably for viral diseases and cancer. In addition to their desired immune effects, interferons cause a number of toxicities, including prominent effects on the nervous system. METHODS: This literature review focused on the incidence of depression associated with interferon treatment. Possible neurochemical mechanisms and remedial strategies were also considered. RESULTS: Interferon treatment, particularly with the alpha subtype, is unquestionably linked with depression, but the strength of association is uncertain because of erratic ascertainment and pretreatment co-morbidity. A likely pathogenic mechanism has been described, involving interferon suppression of serotonin synthesis. Controlled treatment trials of interferon-induced depression are not yet available. CONCLUSIONS: Neurotoxicity substantially limits the use of interferons. At least some of the risk of depression appears to derive from their anti-serotonergic effects, consistent with the large body of evidence pointing to a general link between serotonin and affective illness. Vigilant detection and aggressive treatment of depression is necessary to optimize interferon treatment of many patients.