The core pathogenic process in the common marmoset model of multiple sclerosis (MS) is the activation of memory-like T cells specific for peptide 34 to 56 derived from the extracellular domain of myelin/oligodendrocyte glycoprotein (MOG(34-56)). Immunization with MOG(34-56) in incomplete Freund's adjuvant is a sufficient stimulus for in vivo activation of these T cells, together with the induction of MS-like disease and CNS pathology. Ex vivo functional characteristics of MOG(34-56) specific T cells are specific cytolysis of peptide pulsed target cells and high IL-17A production. To indentify possible functions in this new model of T helper 1 cells, which play a central pathogenic role in MS models induced with complete Freund's adjuvant, we tested the effect of human interferon-gamma (IFN gamma) administration during disease initiation of the disease (day 0-25) and around the time of disease expression (psd 56-81). The results show a clear modulatory effect of early IFN gamma treatment on humoral and cellular autoimmune parameters, but no generalized mitigating effect on the disease course. These results argue against a prominent pathogenic role of T helper 1 cells in this new marmoset EAE model.