Abstract
Purpose: :
Microglia comprise the vast majority of innate immune cells in the quiescent retina, but another population can be detected; the GFP+ dendritic cells in CD11c-DTR mice whose GFP expression is controlled by the CD11c promoter. The activities of these cells are largely unknown, but they are the principal rapid responders to retinal injury. Here we examine their properties and demonstrate a similar population in brain.
Methods: :
Retina and brain from CD11c-DTR mice are collected from normal and treated mice, and examined by immunofluorescence and flow cytometry. The treatments include optic nerve crush, needle stick, and light exposure. Spleen cells and antibody isotypes were used as positive and negative controls for staining.
Results: :
In quiescent retina, more than 5 times as many GFP+ cells are present, relative to MG, than in brain. The GFP+ cells in retina and brain are similar in phenotype; CD45(med), class II(lo), Gr-1(lo), CD11c(lo), and CD11b(hi). After an injury (ONC), the GFP+ cells in retina substantially increase in the CD45(med) population, and upregulate class II. They are CD11b(hi), CD11c(lo), and GR-1(lo). The frequency of cells in the CD45(hi) population increases, and Gr-1(hi) cells appear. The GFP+ cells remain in the Gr-1(lo) population. Light damage leads to a large increase in GFP+ cells in the OPL, and a smaller increase in inner retina. IRBP-KO mice exhibit a progressive retinal degeneration. Even though there is no evidence of inflammation on H&E staining, there is an increase in CD45+ cells. The MG in the CD45(med) are minimally affected; cells in the CD45(hi) population show the most differences; increase in number and class II+. An acute local injury to the brain via a needlestick to the superior colliculus showed an intense localization of GFP+ cells at the site of injury. The most significant increase was in the CD45(hi), CD11c(hi), GFP+ cells, suggesting they were recruited from the circulation.
Conclusions: :
The most reactive population to a wide variety of challenges to the retina or brain was the GFP+ population in CD11c-DTR mice, whether from resident or recently-recruited cells. Overall, the frequency of the GFP+ cells was lower in brain than retina, but injury led to an increased number of GFP+ cells in both tissues. More severe injury led to GFP+ cells in the CD45(hi) population.
Keywords: microglia • retina • immunohistochemistry