Acute effects of low-dose interferon-alpha on serum cortisol and plasma interleukin-6

Major depression is associated with both hypothalamic-pituitary-adrenal (HPA) axis overactivity and immune system activation. Depression is a common occurrence following interferon (IFN)-a treatment. While IFN-alpha is known to stimulate the HPA axis, little is known about the effects of exogenous IFN-a in humans on the proinflammatory cytokine interleukin (IL)-6, a marker of immune system activation. This study examined the acute effects of IFN-alpha on cortisol and IL-6 release, and the time course of any changes in these variables. Serum cortisol and plasma IL-6 were assessed in healthy volunteers over an 8-h period following 3 million units subcutaneous IFN-alpha or placebo using a double-blind, placebo-controlled crossover design. IFN-alpha resulted in a significant increase in both cortisol and IL-6. Regular sampling over 8 h did not delineate any sequential effect of the rise in these variables over time. We conclude that IFN-alpha acutely stimulates both the HPA axis and proinflammatory cytokine release. The hypothesis that the effect of IFN-alpha on the HPA axis is indirect and mediated by IL-6 was not supported by this study. Our findings are nonetheless of relevance to the aetiology of depression following IFN-alpha.