Mechanisms of immune system activation in glaucoma: oxidative stress-stimulated antigen presentation by the retina and optic nerve head glia.

PURPOSE: Evidence supports the immune system activity accompanying glaucomatous neurodegeneration. This study aimed to determine the in vitro effects of reactive oxygen species (ROS) on the phenotype and antigen-presenting function of the retina and optic nerve head glia.
METHODS: Cultures of rat retina and optic nerve head glia were treated with a mixture of ROS-generating compounds for 24 and 48 hours. Pretreated glial cells were then coincubated with syngeneic CD4(+) T cells for 48 hours. ROS generation and cell viability were assessed with the use of dihydroethidium and calcein assays, respectively. Flow cytometry and immunocytochemistry were used to determine major histocompatibility complex (MHC) class II molecules. In addition, functional experiments were performed to determine the proliferation and cytokine secretion of T cells using [(3)H]-thymidine incorporation and TNF-alpha assays, respectively.
RESULTS: MHC class II molecules were upregulated on glial cells exposed to ROS. Compared with the control glia, glial cells in ROS-generating systems were found to be more potent inducers of T-cell activation in a cell density- and time-dependent manner, as assessed by increased T-cell proliferation (approximately threefold) and TNF-alpha secretion (approximately sixfold; P < 0.01). When an ROS scavenging treatment was applied, MHC class II upregulation on glial cells persisted, but antigen-mediated T-cell activation was significantly decreased (P < 0.01), indicating an additional costimulatory function of ROS during antigen presentation.
CONCLUSIONS: These in vitro findings support that ROS regulate the immune response by stimulating the antigen-presenting ability of glial cells and functioning as costimulatory molecules for antigen presentation.