CX3CR1⁺ MNCs colocalize with hematopoietic progenitors at the perivascular region. (A) Two-photon intravital microscopy of the colocalization of adoptively transferred LSK cells (blue) and host CX3CR1⁺ MNCs (green) in the cranial BM cavities of Cx3cr1^GFP/+ mice. Scale bar, 50 µm. Data are representative of 2 independent experiment with similar results. (B-D) Immunofluorescence images of the femoral section of Cx3cr1^GFP/+ mice. (B) CX3CR1⁺ MNCs (green) and blood vessel (red). Dashed line indicates the bone line. (C-D) CX3CR1⁺ MNCs (green), FLT3 (blue), c-KIT (red), and LIN⁺CD41⁺ cells (gray). Yellow arrow indicates a MPP cell. (D) White boxed areas show that MPP cells make contact with CX3CR1⁺ MNCs. Yellow arrowheads indicate MPP cells. The small images in the right (C) and far right (D) columns show the same sections labeled with each indicated molecule. Scale bars, 10 µm (C), 20 µm (B,D). Data are representative of 6 sections from 3 (B) or 4 (C) mice with similar results. (E) Average distance between the nearest CX3CR1⁺ cells and MPPs or LIN⁺CD41⁺ cells in the BM of Cx3cr1^GFP/+ mice within 20 μm. Circles represent individual cells analyzed from 6 sections from 4 mice (n = 203 LIN⁺CD41⁺ cells; n = 44 MPPs). Data are mean ± standard error of the mean. The P value was determined using an unpaired Student t test.