Antigen presentation by CD40⁺MHC-II⁺ astrocytes promotes CNS autoimmunity

Astrocytes contribute to the pathology of multiple neurological disorders, including the T cell-driven autoimmune disease of the central nervous system (CNS) multiple sclerosis and its mouse model, experimental autoimmune encephalomyelitis¹. However, little is known about functional interactions between astrocytes and CD4⁺ T cells. Here using rabies barcode interaction detection followed by sequencing², in combination with single-cell RNA sequencing, in vitro co-culture systems and cell-specific in vivo CRISPR-Cas9-based genetic perturbation studies, we established that astrocytes expressing CD40 and MHC-II promote CNS T cell autoimmunity. We harnessed universal labelling immune partnerships by SorTagging intercellular contacts³ to analyse astrocyte-interacting CD4⁺ T cells, finding that direct astrocyte-CD4⁺ T cell interactions enhance pathogenic T helper 17 cell responses in experimental autoimmune encephalomyelitis. In addition, we studied the effect of these interactions on astrocytes. Using in vivo subproteomic approaches⁴ and AlphaFold-Multimer predictions⁵, we established that CD40 activation in astrocytes by CD40L expressed by CD4⁺ T cells induces the accumulation of PLIN4-positive lipid droplets, which provide acetyl-CoA to promote p65 acetylation-dependent NF-κB activation and antigen presentation. Finally, we detected CD40⁺MHC-II⁺LD⁺ astrocytes in multiple sclerosis samples by single-nucleus RNA sequencing and immunohistochemistry. In summary, these studies define a previously unrecognized mechanism by which astrocytes promote CNS autoimmunity.