Pathogenic mechanisms in neuronal surface autoantibody-mediated encephalitis

In recent years, autoimmune encephalitis associated with antibodies against neuronal cell surface proteins has become a well-recognized phenomenon. Here, we describe clinical features and diagnosis of these conditions before turning to the mechanisms by which autoantibodies are generated and cause disease. The clinical syndrome typically evolves in a subacute fashion and is quite variable, although short-term memory loss, behavioral changes, and seizures are common. Laboratory and imaging parameters of inflammation are typically less overtly deranged than in infectious encephalitis. While the most common antibodies found are to the NMDA receptor or LGI1 protein, a growing number of autoantibodies have been described. Established triggers include tumors and infections, although in many cases neither is identified. It is becoming increasingly clear that host immunogenetics can play a part in disease susceptibility, with a prominent role of HLA haplotype in certain syndromes. Antibodies cause disease by several mechanisms, including direct blocking of ligand binding sites, receptor internalization, and activation of complement, governed in part by the subtype of IgG antibody present. Although in vitro and in vivo models have contributed to our understanding of the mechanisms of disease, numerous gaps in our knowledge of the immunopathogenesis remain, and newer disease models are needed. Insights gained from such approaches will inform our basic understanding of disease and will likely also translate into diagnostic and therapeutic advances.