Expression of major histocompatibility complex molecules in rodent retina. Immunohistochemical study.

PURPOSE In Lewis rats, S-antigen-induced intraocular inflammation, which occurs initially in the retina, is mediated by T cells requiring major histocompatibility complex (MHC)-restricted antigen presentation. In such organ-specific inflammation, antigen presentation may take place at the site of the initial inflammatory response. In the present study an attempt was made to determine the presence of the putative antigen-presenting cells in the retina of rats. METHODS Six bone marrow chimeras were constructed by transferring 50 x 10(6) donor [Lewis x Brown Norway, (LBN) F1] bone marrow cells into lethally irradiated Brown Norway rats. Three chimeras, 3 Lewis, and 2 Brown Norway rats each received intravenous injections of gamma interferon (IFN-gamma) at a dose of 2 x 10(5) U/rat, 48 and 24 hours before enucleation of the globes. Enucleated globes from the 3 remaining untreated chimeras, 21 additional Lewis rats, and 6 Brown Norway rats served as controls. Retinas from all globes were prepared for either wholemount or cryosectioning and were stained using various primary antibodies, including anti-Lewis MHC class II (OX3), anti-rat MHC class II (OX6), anti-Lewis MHC class I (II-69), anti-rat MHC class I (OX18), anti-macrophage complement receptor 3 (OX42), anti-monocytes/macrophages (ED1, ED2, and ED3), and anti-glial fibrillary acidic protein (GFAP). Fluorescein-conjugated goat anti-mouse and rhodamine-conjugated anti-rabbit immunoglobulins were used to detect the monoclonal or polyclonal antibodies, respectively. All the specimens were examined under Zeiss confocal laser scanning microscopy. The positively stained cells were counted for quantitative analysis. RESULTS Major histocompatibility complex class II (OX6)-positive cells were demonstrated in the wholemount retinas of IFN-gamma-untreated chimeras, Lewis, and Brown Norway rats. These cells showed a dendritic morphology and increased significantly in number in IFN-gamma-treated Lewis and Brown Norway rats. Expression of Lewis-specific class I (II-69) and class II (OX3) molecules was detected in a few perivascular cells in the retina of chimeric rats treated with IFN-gamma. Most dendritic cells in the retina expressed the macrophage markers, ED1 and OX42, without IFN-gamma treatment. However, vascular endothelia, retinal pigment epithelia, Müller cells, and astrocytes stained neither by Class II molecules nor by macrophage markers. The vascular endothelium and retinal pigment epithelium was found to express constitutively class I molecules (OX18). CONCLUSIONS A subpopulation of retinal microglia can express MHC class II molecules. Only a few of these are derived from bone marrow. Retinal microglial cells, particularly those derived from bone marrow, may participate in antigen presentation and the subsequent development of retinitis, as seen in S-antigen-induced experimental autoimmune uveoretinitis.