Sickness behavior and chronic immune diseases are frequently associated with depressive symptomatology. In addition, immune activation by single cytokine therapies, such as treatment of malignancies and hepatitis C with interferon-alpha (IFN-α) often induces significant changes in emotional reactivity and affect. However, underlying pathogenic mechanisms of cytokine-induced brain dysfunction largely remain unknown.We presently demonstrate the induction of anxiety- and depressive-like behavior in male BALB/c mice after prolonged treatment with murine IFN-α for up to four weeks. Subsequently, neural and cellular communication routes between the immune system and the brain were examined.IFN-α induced anxious and depressive-like behavior in a light dark, open field, tail suspension, and novel object paradigm with a maximum effect after two weeks of treatment. Effect sizes of IFN-α varied between variables from 23 to 41%. Behavioral deficits were not prevented by complete vagotomy, or by blocking leukocyte function-associated-1 (LFA-1)/intercellular adhesion molecule-1 (ICAM-1) and activated leukocyte cellular adhesion molecule (ALCAM)-mediated cellular adhesion events, which are both involved in immune cell entry to the brain.We demonstrate emergence of anxiety- and depressive-like behavior in a mouse model of sustained IFN-α application allowing investigation of its pathogenic mechanisms, which is of clinical importance. We failed to demonstrate a critical effect for the vagus nerve or adhesion molecules, but current experiments do not allow excluding the vagus nerve as an afferent communication route. Future studies are needed to unveil if both pathways can be completely excluded in the etiology of behavioral deficits induced by IFN-α.