Induction of HLA-DR expression in human lamina cribrosa astrocytes by cytokines and simulated ischemia.

PURPOSE: Recent evidence strongly suggests that activated immunity occurs during the neurodegenerative process of glaucomatous optic neuropathy. Although activation of lamina cribrosa astrocytes has been identified in glaucomatous optic nerve head, their role on the activated immune responses seen in glaucoma patients is unknown. Here, the authors aimed to study the potential role of lamina cribrosa astrocytes as a component of activated immune responses seen in glaucoma patients.
METHODS: Expression of HLA-DR in optic nerve head astrocytes was studied using immunohistochemistry in postmortem eyes of patients with glaucoma and normal donors. Serum cytokine levels of patients with glaucoma and control subjects were measured using enzyme-linked, immunosorbent assay. In addition, in vitro experiments were performed using astrocyte cultures derived from human optic nerve head or fetal human brain. The cultured astrocytes were incubated under selected stress conditions such as exposure to cytokines, IFN-gamma and IL-10, or simulated ischemia for up to 48 hours. The expression of HLA-DR was studied in these cells using flow cytometry and immunocytochemistry.
RESULTS: Immunohistochemistry demonstrated an upregulation of the HLA-DR expression in the optic nerve head astrocytes in glaucoma. In addition, serum levels of IL-10 was higher in the patients with normal pressure glaucoma compared to age-matched control subjects (P: = 0.001). Regarding in vitro experiments, unlike brain astrocytes, the percentage of cells expressing HLA-DR was approximately 3 times higher in the cultures of optic nerve head astrocytes exposed to simulated ischemia compared to cultures incubated under normal conditions (P: = 0.09). Incubation with IFN-gamma induced HLA-DR expression in brain and lamina cribrosa astrocytes, up to 25-fold, (P < 0.001) either in the absence or presence of simulated ischemia. Induction of HLA-DR expression by IL-10 was approximately 6 times higher in lamina cribrosa astrocytes incubated under simulated ischemia compared to that incubated under normal condition (P: = 0.004) and was not prominent in brain astrocytes.
CONCLUSIONS: These findings suggest that optic nerve head astrocytes function as antigen-presenting cells and that their immunogenic capacity is more sensitive to ischemia than brain astrocytes. Taken together, these findings provide novel evidence that regulation of immunogenic capacity of optic nerve head astrocytes by cytokines or ischemic stress may have a role during the neurodegeneration process in patients with glaucoma.