Expansion of HSPCs with higher repopulating capacity occurs before lupus onset. Eight- to 10-week-old B6 and healthy TC mice were used for this study. (A) Percentages of LSK cells in the BM of B6 and TC mice are displayed as mean ± SD in contour plots. Right panel shows the total number of BM LSK cells with each dot symbolizing the value from 1 mouse. (B) B6 and TC mice were labeled with BrdU for 16 hours. The histogram shows a representative profile of BrdU staining of LSK cells. The percentage of BrdU⁺ cells in the BM LSK population in B6 and TC mice is shown by individual open and closed dots. (C) Competitive transplantation was done by transferring 10⁶ BM cells from TC mice (CD45.2⁺) together with 10⁶ BM cells from B6.SJL mice (CD45.1⁺) into irradiated B6.SJL F1 mice (CD45.1⁺). Hematopoietic repopulation by cotransferred TC and B6.SJL BM cells was analyzed 18 weeks after transplantation by determining the percentages of CD45 isotype expressing PBL. Each dot corresponds to the percentage of donor-derived BM LSK cells in each mouse. (D) The frequencies of donor-derived PBL in recipients at each round of serial transplantation are shown by gray bars representing the mean ± SD (n = 6). (E) An equal number of LSK cells purified from TC or B6 mice were cultured in medium containing 50 ng/mL stem cell factor, 10 ng/mL IL-6 and 10 ng/ml IL-3. Seven days later, cells were harvested and counted. A total of 10⁶ cells derived from TC or B6 LSK cells were transferred into irradiated B6.SJL mice. Reconstitution was examined 10 months later. Left: Bars depict the number of total nucleated cells harvested from the 7-day culture. Right: Bars show the percentage of donor-derived PBL. Data are presented as mean ± SD (n = 4).