Peripheral blood mononuclear cell secretome from patients with autoimmune encephalitis promotes seizures in vitro

Autoimmune encephalitis (AE) is characterized by inflammatory processes in the central nervous system and frequently presents with seizures. Even though an ictogenic potential has been shown for some antibodies against neuronal surface antigens (NSAbs), AE pathophysiology is complex, and NSAbs-independent mechanisms are likely to contribute to seizures. We investigated whether the secretome released by peripheral blood mononuclear cells (PBMCs) from AE patients contributes to seizure generation independently of NSAbs.

PBMCs were isolated from 19 patients with AE (including both those with and those without detectable NSAbs) and 13 healthy volunteers. After 6 h in culture, the PBMC supernatant (secretome) was infused into a heterologous in vitro whole guinea pig brain preparation. Neurophysiological activity was monitored in the isolated in vitro guinea pig brain preparation during coperfusion of PBMC-derived supernatant (secretome) with the endotoxin lipopolysaccharide and human recombinant serum albumin, to induce and mimic, respectively, a mild functional blood-brain barrier impairment. Morphological analysis of ionized calcium-binding adapter molecule 1-positive glial cells was performed in these brains after the electrophysiological experiment. Secretome obtained after 6 h in culture was analyzed with the Multiplex ELLA array system for inflammatory mediator detection.

Electrophysiological recordings and immunofluorescence analyses revealed that the secretome from PBMCs derived from AE patients induced seizurelike events and microglial activation in our in vitro brain preparation. Multiplex ELLA immunoassay analysis showed significantly lower concentration of interleukin (IL)-10, IL-1Ra, tumor necrosis factor-α, IL-2, and IL-6 in the secretome of PBMCs derived from AE patients compared to healthy subjects. IL-1β levels were comparable in the secretome of PBMCs derived from AE and healthy subjects.

Our findings suggest, for the first time, that peripheral inflammatory mediators could represent a trigger factor for seizure activity in AEs, beyond a possible antibody-mediated mechanism.