Neuronal pSTAT1 hallmarks synaptic pathology in autoimmune encephalitis against intracellular antigens.

Autoimmune encephalitis (AE) is an inflammatory syndrome of the central nervous system (CNS) triggered by aberrant immune responses against neuronal intracellular (IC-AE) or surface (NS-AE) autoantigens. The resulting neuronal alterations and clinical trajectories differ, with IC-AE often leading to fatal outcomes. Unfortunately, the scarce availability of tissue from AE cases has hampered systematic analyses that would allow an understanding of the pathogenesis underlying neuronal alterations in T cell-mediated AE syndromes. Here, we assembled a cohort comprising both NS-AE (n = 8) and IC-AE (n = 12) from multiple institutions to delineate key histopathological features that distinguish neuronal pathology between IC-AE and NS-AE. In contrast to NS-AE, IC-AE lesions present a prominent neuronal pSTAT1 signature, accompanied by a high proportion of brain-resident memory CD8 + T cells and neurodegenerative GPNMB + phagocytes which show synaptic engulfment with little C3-complement deposition. Our findings highlight distinct histopathological features of IC-AE compared to NS-AE, providing actionable biomarkers for diagnostics and treatment strategies.