Expression of macrophage migration inhibitory factor in rat retina and its immunohistochemical localization

Macrophage migration inhibitory factor (MIF) plays an important regulatory role for the T-cell activation induced by mitogenic or antigenic stimuli. We examined expression of MIF in rat retina. Reverse transcription-polymerase chain reaction analysis of a retinal tissue homogenate revealed that MIF mRNA was constitutively expressed. A single band specific for MIF protein was also observed by Western blot analysis. Immunohistochemistry using frozen sections of retinal tissues reacted with an anti-rat MIF antibody showed that MIF was localized in astrocytes, Muller cells and pigment epithelial (RPE) cells. This topological finding was confirmed by colocalization of MIF protein with glial fibrillary acidic protein and vimentin, which are putative immunohistochemical 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 inflammatory and immunological responses in the retina. Considering these facts, constitutive expression of MIF in these cells suggested the possibility that the protein contributes to regulation of retinal tissue inflammation as well as its local immunity.