Fig. 1. Immunostaining of mouse triangularis sterni muscles with 2166 antibody reveals capping cells at NMJs. (A) Low-power confocal projection showing numerous 2166-positive interstitial cells and a prominent subpopulation in the vicinity of NMJs. (B) High-power confocal projection images of NMJ-capping cells (green), juxtaposed with motor endplates counterstained with TRITC--BTX (red). (C) Triple-stained NMJ with axon stained with neurofilament antibodies (red), NMJ-capping cell (green) and motor endplate AChR stained with Alexa Fluor 647--BTX (blue). (D,E) Other interstitial and endothelial cells with positive 2166 immunostaining were scattered at low density throughout the muscles. (F) Quantification of density of NMJ-capping cells at motor endplates. All endplates showed at least one and most were associated with only one NMJ-capping cell; no NMJ was associated with more than three of these cells. Scale bars: 100 µm (A); 20 µm (E, applies also to B-D).