Resilient recipient Mφs are located within perivascular and endosteal regions of the BM and proliferate autonomously after irradiation and transplantation. (A-C) Representative immunohistochemistry staining using anti-GFP (A), anti-F4/80 (B), and anti-ER-HR3 antibodies (C) in serial femoral BM sections from 5 week posttransplant recipient MacGreen mice. GFP⁺ recipient Mφs expressing F4/80 and ER-HR3 in HSC-enriched endosteal (arrowheads) and perivascular (arrows) regions (A-C, original magnification ×60). All sections were counterstained with hematoxylin (blue). (D) Representative flow cytometry analysis of BM myeloid populations gated as per Table 1 showing cell cycle gating using Ki67 and Hoechst 33342 (Ho) staining. Ki-67^negHo^low cells (blue gate) represent cells in G₀ phase, Ki-67⁺Ho^low cells (yellow gate) are in G₁ phase, and Ki-67⁺Ho⁺ cells (pink gate) are in S/G₂/M phase of the cell cycle. Representative dot plots show naive (no-Tx) MacGreen Mφs (i), 4 week posttransplant recipient (Rec Mφs; ii) and donor Mφs (iii), no-Tx MacGreen granulocytes (iv), 4 week posttransplant donor granulocytes (v), no-Tx MacGreen EIMs (vi), 4 week posttransplant Rec (vii) and donor (viii) EIMs, no-Tx MacGreen monocytes (ix), and 4 week posttransplant donor monocytes (x). (E) Percentage of no-Tx MacGreen, 4 week posttransplant recipient (Rec) and donor (donor) BM resident Mφs (i), EIMs (ii), monocytes (iii), and granulocytes (iv) in phase G₀ (blue bar), G₁ (yellow bars), or S/G₂/M (pink bars). Data represent mean ± SD of n = 3 mice. Flow cytometry plots and histograms are from a representative animal, and the percentage of positive cells is based on the proceeding parent population. Statistical analysis was performed using 1-way ANOVA and a Tukey’s multiple comparison test on S/G₁/M phase, where asterisks indicate significant differences from nontransplanted mice (*P < .05 and ***P < .001). Data were collected from a single experiment with 3 animals per group, and 300 000 events were collected by flow cytometry.