Differential effect of inflammation and Epo injections on spleen and bone marrow erythroblast maturation. The proportion of Ter119⁺ cells (A,C) and the number of erythroblasts at different stages of maturation (B,D) were analyzed in bone marrow (A-B) and spleen (C-D) cells. The proportion of erythroblasts at each stage of maturation was determined by FACS (supplemental data), and the corresponding number of erythroblasts was calculated based on the observation that a femur contains 20 × 10⁶ cells and a spleen contains 10⁶ cells/mg wet weight. The 3 stages cor-respond to early (Ery A), intermediate (Ery B), and late erythroblasts (Ery C). Results are shown for control mice (C), ZIGI mice killed 5 days (Z5), 9 days (Z9), 12 days (Z12), and 17 days (Z17) after zymosan injection, Epo-treated control mice (Epo1 and Epo4), and ZIGI mice treated with Epo (Z9Epo1; Z12Epo4; Z17Epo9). Data are mean ± SEM for 4 to 8 mice per group per time point. *P < .005 between Z9 and Z9Epo1 for Ery A and Ery B.