The NF-kappa B/REL-family of transcription factors plays a central role in coordinating the expression of a wide variety of genes controlling immune responses including autoimmunity of the central nervous system (CNS). The inactive form of NF-kappa B consists of a heterodimer which is complexed with its inhibitor, I kappa B. Conditional knockout-mice for I kappa B alpha in myeloid cells (IysMCreI kappa B alpha(fl/fl)) have been generated and are characterized by a constitutive activation of NF-kappa B proteins allowing the study of this transcription factor in myelin-oligodendrocyte-glycoprotein induced experimental autoimmune encephalomyelitis (MOG-EAE), a well established experimental model for autoimmune demyelination of the CNS. In comparison to controls, IysMCreI kappa B alpha(fl/fl) mice developed a more severe clinical course of EAE. Upon histological analysis on day 15 p.i., there was an over two fold increased infiltration of T-cells and macrophages/microglia. In addition, IysMCreI kappa B alpha(fl/fl) mice displayed an increased expression of the NF-kappa B dependent factor inducible nitric oxide synthase in inflamed lesions. These changes in the CNS are associated with increased numbers of CD11b positive splenocytes and a higher expression of Ly6c on monocytes in the periphery. Well in accordance with these changes in the myeloid cell compartment, there was an increased production of the monocyte cytokines interleukin(IL)-12 p70, IL-6 and IL-1beta in splenocytes. In contrast, production of the T-cell associated cytokines interferon gamma (IFN-gamma) and IL-17 was not influenced. In summary, myeloid cell derived NF-kappa B plays a crucial role in autoimmune inflammation of the CNS and drives a pathogenic role of monocytes and macrophages independently from T-cells.