Glia Modulates Immune Responses in the Retina Through Distinct MHC Pathways

Glia antigen-presenting cells (APCs) are pivotal regulators of immune surveillance within the retina, maintaining tissue homeostasis and promptly responding to insults. However, the intricate mechanisms underlying their local coordination and activation remain unclear. Our study integrates an animal model of retinal injury, retrospective analysis of human retinas, and in vitro experiments to gain insights into the crucial role of antigen presentation in neuroimmunology during retinal degeneration (RD), uncovering the involvement of various glial cells, notably Müller glia and microglia. Glial cells act as sentinels, detecting antigens released during degeneration and interacting with T-cells via MHC molecules, which are essential for immune responses. Microglia function as APCs via the MHC Class II pathway, upregulating key molecules such as Csf1r and cytokines. In contrast, Müller cells act through the MHC Class I pathway, exhibiting upregulated antigen processing genes and promoting a CD8⁺ T-cell response. Distinct cytokine signaling pathways, including TNF-α and IFN Type I, contribute to the immune balance. Human retinal specimens corroborate these findings, demonstrating glial activation and MHC expression correlating with degenerative changes. In vitro assays also confirmed differential T-cell migration responses to activated microglia and Müller cells, highlighting their role in shaping the immune milieu within the retina. In summary, our study emphasizes the involvement of retinal glial cells in modulating the immune response after insults to the retinal parenchyma. Unraveling the intricacies of glia-mediated antigen presentation in RD is essential for developing precise therapeutic interventions for retinal pathologies.