Intravital microscopy of the parietal BM in NOD/SCID mice. (a) Low-power view (2× objective) of the murine parietal bone. The sagittal suture (SS), which joins both parietal bones, appears dark due to the blood circulating in the underlying sagittal sinus. The midparietal area (box) viewed at higher magnification (10× objective) in (b) represents the area of the parietal bone typically used for the IVM recordings. This area comprises several collecting venules (Cv) and sinusoids (S). (c and d) Engraftment of the NOD/SCID skull microvasculature with BM nucleated cells from EGFP-Tg mice. Sublethally irradiated NOD/SCID mice were transplanted with BM nucleated cells from EGFP-Tg mice. (c) Two weeks after injection, donor cells have engrafted the parasagittal regions and also the midparietal area (box) shown at higher magnification in (d). Note that the microvessels are masked by green fluorescent hematopoietic cells. (e–g) Human CD34⁺ cell rolling in a NOD/SCID collecting venule. CFSE-labeled CD34⁺ cells purified from mPB samples were injected via the carotid artery and visualized (10× objective) in the midparietal area of a NOD/SCID mouse. (e) A free-flowing CD34⁺ cell (t = 0 s) in the central Cv (f) tethers to the vessel wall (0.30 s), and (g) rolls during the following 0.53 seconds. The white arrow marks the initial site of interaction. Supplemental data of a video depicting the BM intravital microscopy model can be downloaded at http://www.jci.org/cgi/content/full/110/4/559/DC1. Bars in a and c, 500 μm; bars in b, d, and g, 100 μm.