Microglia promote autoimmune inflammation via the noncanonical NF-κB pathway.

Microglia have been implicated in neuroinflammatory diseases, including multiple sclerosis and its animal model experimental autoimmune encephalomyelitis (EAE). We demonstrate that microglia mediate EAE disease progression via a mechanism relying on the noncanonical nuclear factor kB (NF-κB) pathway. Microglia-specific deletion of the noncanonical NF-κB-inducing kinase (NIK) impairs EAE disease progression. Although microglial NIK is dispensable for the initial phase of T cell infiltration into the central nervous system (CNS) and EAE disease onset, it is critical for the subsequent CNS recruitment of inflammatory T cells and monocytes. Our data suggest that following their initial CNS infiltration, T cells activate the microglial noncanonical NF-κB pathway, which synergizes with the T cell-derived cytokine granulocyte-macrophage colony-stimulating factor to induce expression of chemokines involved in the second-wave of T cell recruitment and disease progression. These findings highlight a mechanism of microglial function that is dependent on NIK signaling and required for EAE disease progression.