Reduction of Gr1^low monocytes in absence of CX₃CR1 is due to impaired cell survival. (A) Comparison of wt and cx₃cr1^gfp/gfp monocytes in mixed BM chimera blood. BM cells were isolated from either wt or cx₃cr1^gfp/gfp donors, mixed to 1:1 ratio from each genotype and transferred into irradiated wt recipients. Eight weeks after transfer recipient mice were bled, and their blood content was analyzed. Dot plot shows discrimination between GFP-positive cx₃cr1^gfp/gfp monocytes (R5 gated cells) and GFP-negative wt monocytes (R6 gated cells). Bar diagram shows percentage of Gr1^low monocytes (as gated in R4, Figure 1A) of either total wt (R6 gated cells, ■) or cx₃cr1^gfp/gfp (R5 gated cells, ) monocytes; n = 8. (B) Comparison of monocyte levels in presence and absence of CX₃CL1. Wt and cx₃cl1^−/− irradiated mice received 1:1 mix of BM cells from wt and cx₃cr1^gfp/gfp mice, and were bled 8 weeks later. Bar histogram shows percentage of Gr1^low monocytes (R4 gated cells, Figure 1A) of total monocytes (R2 gated cells, Figure 1A) of wt (■) and cx₃cl1^−/− (□) recipients of either wt or cx₃cr1^gfp/gfp BM cells; n = 5. (C) Comparison of blood and BM monocytes of cx₃cr1^gfp/+ () and cx₃cr1^gfp/gfp () littermates. Bar diagram shows the percentage of Gr1^low cells (gated in R4, Figure 1A) out of total blood or BM monocytes (cells gated in R2, Figure 1A); n = 4. (D) Comparison of monocytes of hMRP8bcl2-transgenic cx₃cr1^gfp/gfp and cx₃cr1^gfp/+ mice. Bar histogram shows percentage of Gr1^low monocytes (cells gated in R4, Figure 1A) of total monocytes (cells gated in R2, Figure 1A) of cx₃cr1^gfp/+ () and cx₃cr1^gfp/gfp () mice, either hMRP8bcl2-transgenic (right bars) or nontransgenic (left bars); n = 3. *P < .0013 **P < .001, ***P < < .005 (Student t test).