EXPRESSION OF MACROPHAGE-MIGRATION INHIBITORY FACTOR IN RAT RETINA AND ITS IMMUNOHISTOCHEMICAL LOCALIZATION

Macrophage migration inhibitory factor (MIF) plays an important regula tory role for the T-cell activation induced by mitogenic or antigenic stimuli. We examined expression of MIF in rat retina. Reverse transcri ption-polymerase chain reaction analysis of a retinal tissue homogenat e revealed that MIF mRNA was constitutively expressed. A single band s pecific for MIF protein was also observed by Western blot analysis. Im munohistochemistry using frozen sections of retinal tissues reacted wi th an anti-rat MIF antibody showed that MIF was localized in astrocyte s, Muller cells and pigment epithelial (RPE) cells. This topological f inding was confirmed by colocalization of MIF protein with glial fibri llary acidic protein and vimentin, which are putative immunohistochemi cal markers for astrocytes and Muller sells. It is well known that the retinal glial cells, as well as RPE cells, play an active role in inf lammatory and immunological responses in the retina. Considering these facts, constitutive expression of MIF in these cells suggested the po ssibility that the protein contributes to regulation of retinal tissue inflammation as well as its local immunity.