The aim of this study was to measure the activity of 2',5'-oligoadenylate synthetase (2',5'AS) which is mainly induced by interferon (IFN)-α and -β in patients with major depression and evaluate its relationship to the disease. 2',5'AS activity of 23 patients (male = 11, female = 12) with major depression and of 29 normal control subjects (male = 15, female = 14) was measured in peripheral blood mononuclear cells (PBMCs) by radioassay. The mean 2',5'AS activity in the PBMCs of the patients and that of the control subjects were 1.10 ± 0.69% and 0.72 ± 0.51%, respectively. The activity in the patients was statistically higher than that of the control subjects (P = 0.03). These results imply some abnormality in the IFN-2',5'AS system of patients with major depression
