Radiation resistance of marginal zone (MZ)-follicular MARCO distribution pathway. BALB/c mice were irradiated and repopulated using rat fetal liver hematopoietic or rat bone marrow cells. The peripheral blood was analyzed by flow cytometry and compared with that of control mice. (A, top pair) Lymphoid (Ly) and myeloid (My) cells were defined according to their size (forward scatter/FSC) and granularity (side scatter/SSC). (A, bottom four) The degree of chimerism is shown on the basis of rat (r) CD45 or mouse (m) CD45 expression in peripheral blood leukocytes (middle/lymphoid gate and lower/myeloid gate density plots, respectively), where the quadrant numbers correspond to the percentage values of gated cells (n=6). (B, C) Splenic sections from 6-weeks post-transplant (B) chimeric and (C) control BALB/c mice stained for MARCO (red) and CR1/2 (green) show the follicular retention of MARCO (arrows) (n=6). Bar size, 50µm.