Interferon-alpha acts at the preoptic hypothalamus to reduce natural killer cytotoxicity in rats

We previously demonstrated that an intracerebroventricular injection of recombinant human interferon-alpha (rhIFN-alpha) reduced the cytotoxicity of splenic natural killer (NK) cells in rats and mice. In the present study, we investigated the brain sites at which rhIFN-alpha acts to suppress splenic NK activity in unanesthetized rats implanted unilaterally with a chronic hypothalamic cannula. A microinjection of 200 U of rhIFN-alpha into the medial part of the preoptic hypothalamus reduced NK activity to approximately 60% of control 30 min after the injection. Administration of 50 U of rhIFN-alpha also decreased NK activity to approximately 80%. The injection of 200 U of rhIFN-alpha into other hypothalamic areas (lateral preoptic hypothalamus, ventromedial hypothalamus, lateral hypothalamus, and paraventricular nucleus) had no effect. The medial preoptic hypothalamus-rhIFN-alpha-induced immunosuppression was completely blocked by splenic denervation, but not by adrenalectomy. These results suggest that IFN-alpha suppresses splenic NK activity predominantly through the medial preoptic hypothalamus-sympathetic pathway.