Translational imaging of TSPO reveals pronounced innate inflammation in human and murine CD8 T cell-mediated limbic encephalitis

Autoimmune-associated epilepsy - a challenging concept

The current International League Against Epilepsy (ILAE) definition and classification guidelines for the first time introduced the category of immune-mediated focal epilepsy in addition to structural, genetic, infectious, and metabolic aetiologies. Moreover, the ILAE Autoimmunity and Inflammation Taskforce recently provided a conceptual framework for the distinction between acute "provoked" seizures in the acute phase of autoimmune encephalitis from chronic "unprovoked" seizures due to autoimmune-associated epilepsy. The first category predominately applies to those autoimmune encephalitis patients with autoantibodies against cell surface neural antigens, in whom autoantibodies are assumed to exert a direct ictogenic effect without overt structural damage. These patients do not exhibit enduring predisposition to seizures after the "acute phase" encephalitis, and thus do not fulfil the definition of epilepsy. The second category applies to those autoimmune encephalitis patients with autoantibodies against intracellular neural antigens and Rasmussen's encephalitis, in whom T cells are assumed to cause epileptogenic effects through immune-inflammation and overt structural damage. These patients do exhibit enduring predisposition to seizures after the "acute phase" of encephalitis and thus fulfil the definition of epilepsy. AAE may result from both, ongoing brain autoimmunity and associated structural brain damage according to the current ILAE definition and classification guideline. We here discuss the difficulties of this concept and suggest an unbiased translationally validated and data-driven approach to predict in an individual encephalitis patient the propensity to develop (or not) AAE and the cognitive and behavioural outcome.

Increased cysteinyl-tRNA synthetase drives neuroinflammation in Alzheimer's disease

BACKGROUND

Microglia-mediated neuroinflammation in Alzheimer's disease (AD) is not only a response to pathophysiological events, but also plays a causative role in neurodegeneration. Cytoplasmic cysteinyl-tRNA synthetase (CARS) is considered to be a stimulant for immune responses to diseases; however, it remains unknown whether CARS is involved in the pathogenesis of AD.

METHODS

Postmortem human temporal cortical tissues at different Braak stages and AD patient-derived serum samples were used to investigate the changes of CARS levels in AD by immunocytochemical staining, real-time PCR, western blotting and ELISA. After that, C57BL/6J and APP/PS1 transgenic mice and BV-2 cell line were used to explore the role of CARS protein in memory and neuroinflammation, as well as the underlying mechanisms. Finally, the associations of morphological features among CARS protein, microglia and dense-core plaques were examined by immunocytochemical staining.

RESULTS

A positive correlation was found between aging and the intensity of CARS immunoreactivity in the temporal cortex. Both protein and mRNA levels of CARS were increased in the temporal cortex of AD patients. Immunocytochemical staining revealed increased CARS immunoreactivity in neurons of the temporal cortex in AD patients. Moreover, overexpression of CARS in hippocampal neurons induced and aggravated cognitive dysfunction in C57BL/6J and APP/PS1 mice, respectively, accompanied by activation of microglia and the TLR2/MyD88 signaling pathway as well as upregulation of proinflammatory cytokines. In vitro experiments showed that CARS treatment facilitated the production of proinflammatory cytokines and the activation of the TLR2/MyD88 signaling pathway of BV-2 cells. The accumulation of CARS protein occurred within dense-core Aβ plaques accompanied by recruitment of ameboid microglia. Significant upregulation of TLR2/MyD88 proteins was also observed in the temporal cortex of AD.

CONCLUSIONS

The findings suggest that the neuronal CARS drives neuroinflammation and induces memory deficits, which might be involved in the pathogenesis of AD.