Detailed characterization of the aberrant CD71^hiTER119^-cell population that accumulates in Trim28 mutant bone marrow. TMC [Trim28^flox/flox:Tg^Mx1Cre (flox/flox:Mx1Cre)] mutant or control [Trim28^flox/flox (flox/flox) and Trim28^flox/+:Tg^Mx1Cre (flox/+:Mx1Cre)] mice at ages 5 to 6 weeks were injected with poly(I:C). Mice were analyzed 2 weeks after the final poly(I:C) administration. (A) Color of cells separated on the basis of CD71 and TER119 expression. Between 4 and 10 × 10⁵ cells were flow sorted and suspended in PBS supplemented with 2% FBS in a 1.5-mL tube and centrifuged to form a pellet. Images were acquired using a Zeiss Stemi SV11 Apo stereomicroscope, AxioCam digital camera, and AxioVision LE software. (B) Flow cytometric analysis of forward scatter (FSC), CD45, cKit, Mac1, and B220 in the CD71^hiTER119^- bone marrow cells of control mice and Trim28 mutant mice. Numbers in the boxed areas indicate the mean percentages of cells in the boxed area calculated by dividing the number of cells in that subpopulation by the number of cells in its immediate ancestor population. (C) The absolute number of different subpopulations in the CD71^hiTER119^- cells was calculated from panels (B) and normalized for total bone marrow cell number. Average with SEM. *indicates statistically significant, P < .05. NS: not significant, P > .05. (D) Neutral benzidine staining of individual cells recovered from flow-sorted populations of different genotype mice treated with poly(I:C). (E) Wright-giemsa staining. Images (D and E) were acquired using an Olympus BX-51 upright light microscope with the 100× oil immersion objective lens, DP-70 high-resolution digital camera, and DP Controller software. (F) Flow cytometric analysis of FSC and CD44 in CD71^hiTER119^- and CD71^hiTER119⁺ cells. Numbers in or near the boxed areas indicate the mean percentage of cells in the boxed area calculated by dividing the number of cells in that subpopulation by the number of cells in its immediate ancestor population. The data represent a summary (C) or representative individuals (A, B, D-F) of more than 3 mice of each genotype examined in 2 to 3 independent experiments.