Figure 9

Physical interaction of microglia-Müller cell processes following microglial activation in vivo. In vivo activation of retinal microglia was induced by intravitreal injection of lipopolysaccharide (LPS, 2 μg in 1 μl of 1 × PBS). Control eyes were injected with 1 μl of 1 × PBS alone. Retinal cryosections were prepared 3 days after injection and immunolabeled with glutamine synthetase (GS) (red) to mark Müller cell processes, Iba-1 (green) to mark microglia, and DAPI (blue) to mark retinal cell nuclei. (A) In PBS-injected control eyes, ramified processes of microglia in the inner retina are oriented predominantly in the horizontal plane of the retina and show minimal interaction or fasciculation with the vertically oriented, GS-positive, Müller cell processes. (B, C) In LPS-injected eyes, microglia in the inner retina demonstrate a more vertical orientation of their processes compared to controls. Microglial processes were observed to be juxtaposed in close physical association with parallel Müller cell processes. Close fasciculation between the vertical processes of both cell types can be observed (arrowheads), suggesting cellular adhesion and physical interaction between Müller cell-microglia processes. In examples in which vertically oriented microglia appear to be migrating in the radial direction, Müller cell processes appear to be acting as a adhesive scaffold that guide microglia orientation and translocation. Scale bar = 10 μM.