Fig. 5

Double-label immunofluorescence of IBA1 and S100; and IBA1 and cytosolic ferritin in DRG of normal controls and FA. a-b normal controls; c-d FA. a and c double-label immunofluorescence of S100 (Alexa Fluor 488 green) and IBA1 (Cy3 red); DAPI (blue); b and d double-label immunofluorescence of IBA1 (Alexa Fluor 488 green) and cytosolic ferritin (Cy3 red). In the normal DRG, IBA1-reactive monocytes may gain access to the S100-reactive satellite cell sheath around neurons (N) but remain separated from the neuronal plasma membrane by a thin layer of satellite cell cytoplasm (a, arrow). IBA1 and S100 show no colocalization. In FA, the outline of the S100-positive satellite cell layer appears irregular and disrupted. An IBA1-reactive monocyte (arrow) abuts or penetrates the neuronal plasma membrane (c). The inset in (c) shows infiltration of a residual nodule by IBA1-positive monocytes. DAPI fluorescence in (c) confirms increased cellularity in FA when compared to the normal DRG (a). A normal DRG shows ferritin immunofluorescence in satellite cells and neurons (N) (b). The mixed yellow and green color suggests that ferritin biosynthesis also occurs in IBA1-positive monocytes. In FA, a multilayered rim of satellite cells around a shrunken neuron (N) is intensely fluorescent for cytosolic ferritin (Cy3 red) (d). Ameboid monocytes express both ferritin and IBA1. The inset in (d) shows matching single-color images in further support of the colocalization of IBA1 (Alexa Fluor 488 green) and ferritin (Cy3 red). Bars (all): 20 μm