VISTA Deficiency Exacerbates Autoimmune Uveitis by Promoting Microglial TLR4/MyD88/NF-κB Activation

Autoimmune uveitis, a leading cause of blindness, is characterized by chronic inflammation within the eye. Current treatments often involve broad immunosuppression, which carries significant side effects and may not fully address the underlying pathology. Microglial activation, a key driver of neuroinflammation, plays a critical role in uveitis progression. VISTA (V-domain Ig suppressor of T cell activation), an immune checkpoint protein, is highly expressed in microglia and is known to regulate inflammatory responses. Understanding how VISTA modulates microglial activity in the ocular environment could reveal novel, targeted therapeutic strategies for this debilitating condition.

Researchers investigated VISTA's role using both in vitro and in vivo models. VISTA expression was initially assessed via flow cytometry in circulating immune cells from VKH patients and healthy controls. For in vitro studies, LPS/IFN-γ-stimulated BV2 microglia were subjected to genetic knockdown, overexpression, or treatment with modulating antibodies (13F3, MH5A). Microglial activation, cytokine secretion (TNF-α, iNOS, COX2), migration, and TLR4/MyD88/NF-κB signaling were then analyzed. An experimental autoimmune uveitis (EAU) mouse model received intravitreal adeno-associated virus-mediated VISTA overexpression, with disease severity evaluated clinically and histopathologically.

VISTA expression was significantly downregulated in circulating immune cells of VKH patients and in retinal microglia during EAU. In vitro, inflammatory stimuli consistently reduced microglial VISTA levels. Genetic knockdown or antibody blockade of VISTA in BV2 microglia exacerbated microglial activation, leading to increased secretion of pro-inflammatory mediators like TNF-α, iNOS, and COX2, and enhanced cellular migration. Conversely, VISTA overexpression or agonism effectively suppressed microglial activation. Critically, in the EAU mouse model, intravitreal VISTA overexpression significantly alleviated disease severity, as confirmed by both clinical and histopathological assessments. Mechanistically, VISTA deficiency was found to potentiate microglial activation by enhancing the TLR4/MyD88/NF-κB signaling pathway, demonstrating a direct link between VISTA and inflammatory cascades.

VISTA deficiency potentiated microglial activation by enhancing TLR4/MyD88/NF-κB signaling, and intravitreal VISTA overexpression alleviated EAU severity.