purpose. Retinal microglial cells of newborn Lewis rats were isolated and cultured, and the effect of macrophage colony-stimulating factor (M-CSF), granulocyte–macrophage colony-stimulating factor (GM-CSF), and interferon-γ (IFN-γ) on microglial expression of the accessory molecules required for antigen presentation were studied.

methods. Retinal microglia were isolated from newborn Lewis rats and cultured in media supplemented with either M-CSF or GM-CSF. Immunohistochemical tests using anti-macrophage complement receptor 3 (OX42) or anti-monocyte–macrophage (ED1) and DiI-ac-low-density lipoprotein (LDL) uptake were used to identify microglia. The effect on accessory molecule expression of microglial cells cultured under varying conditions (M-CSF, GM-CSF, and M-CSF plus IFN-γ) was analyzed by fluorescence-activated cell sorter, using one of the following antibodies: anti-OX3, anti-OX6, anti-rat intercellular adhesion molecule (ICAM)-1, anti-rat B7-1, or anti-rat B7-2.

results. The cultured retinal microglia were positive for macrophage-related antigens (ED1 and OX42) and also showed uptake of LDL. Furthermore, ICAM-1 and B7-2 were expressed constitutively on these cells, and MHC class II and B7-1 were also expressed after IFN-γ stimulation.

conclusions. In vitro, the retinal microglia express the molecules required for effective antigen presentation to CD4-positive T cells. These findings suggest that microglia may play a role in local antigen presentation, especially when they are exposed to IFN-γ.