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

Purpose: VISTA, an immune checkpoint enriched in microglia, regulates inflammatory signaling. Given microglial activation drives autoimmune uveitis, we investigated whether VISTA protects against experimental autoimmune uveitis (EAU) by modulating retinal microglia. Methods: VISTA expression was analyzed by flow cytometry in active VKH patients and healthy controls. Functional studies in LPS/IFN-γ-stimulated BV2 microglia used genetic knockdown/overexpression and modulating antibodies (13F3, MH5A). Activation status, cytokine secretion, migration, and TLR4/MyD88/NF-κB signaling were assessed. An EAU mouse model received intravitreal adeno-associated virus-mediated VISTA overexpression, with severity evaluated clinically and histopathologically. Results: VISTA was downregulated in circulating immune cells of VKH patients and in retinal microglia during EAU. In vitro, inflammatory stimuli reduced microglial VISTA. Its knockdown or blockade exacerbated microglial activation, pro-inflammatory mediator secretion (TNF-α, iNOS, COX2), and migration, while overexpression or agonism suppressed activation. Critically, intravitreal VISTA overexpression alleviated EAU severity. Mechanistically, VISTA deficiency potentiated activation by enhancing TLR4/MyD88/NF-κB signaling. Conclusions: VISTA is a crucial gatekeeper of ocular immune homeostasis. Its downregulation promotes uveitis via microglial TLR4/MyD88/NF-κB pathway activation, making VISTA signaling restoration a promising therapeutic strategy.