Increased in vivo myeloid potential of arthritic LT-HSCs is revealed by old recipient transplantation. (A) Experimental scheme for competitive in vivo transplantation. Donors and recipients have distinct Ly5 alleles. Recipients were generated to be histocompatible with both donors and also express a different Ly5 allele. (B) FACS plot depicting analysis of Ly5 chimerism of bone marrow Mac1⁺ cells in recipient mice 6 days after transplantation. At an early time point (< 10 days after transplantation), peripheral blood was virtually devoid of leukocytes and hence only bone marrow analysis could be performed. (C) Quantification of arthritic and control KSL contribution to Mac1⁺ and B220⁺ cells in bone marrow (BM) and peripheral blood (PB) of young recipients based on Ly5 chimerism. (D) PB chimerism 8 weeks (wks), 16 weeks, and 26 weeks (6 months) after transplantation into old recipients gated on Mac1⁺Gr1^hi myeloid cells or B220⁺ cells. Numbers in red indicate absolute percentage increase in contribution to Mac1⁺Gr1^hi or B220⁺ lineages by arthritic KSL cells compared to contribution by control KSL cells. (E) Statistical analysis to compare the fold contribution to different lineages of arthritic KSL cells relative to control KSL. (F) BM KSL chimerism 26 weeks after transplantation into old recipients; *P < .05, **P < .01, ***P < .001 relative to control KSL-derived cells (see also supplemental Figure 3).