Figure 4. Tumor growth results in expansion of splenic erythroid cell populations in mice.

(A-E) Peripheral blood and tissues were prepared from mice bearing subcutaneous B16 and MC38 tumors of 1,000-2,500 mm³ in size and control (Con) mice without tumor growth. Serum EPO concentrations (n = 5, 3, and 7 for Con, B16 and MC38 mice, respectively) were determined by ELISA (A). Kidney sections were analyzed by immunofluorescence and DNA counterstaining (B). EPO immunofluorescence signals in individual EPO⁺ objects were quantified and shown as mean signal intensities (C). Splenocytes were analyzed by antibody staining and flow cytometry (D). Splenic CD71⁺TER119⁺ cell percentages in individual mice (circle) and their medians (line) are shown (E). Data are representative of three experiments.(F and G) B16 cells were injected into C57BL/6 mice (n = 6-8) to form subcutaneous tumors. An anti-EPO antibody and isotype-matched control (Con) immunoglobulin were administered to mice (every other day, three times in total, and the first dose given when tumor size reached 100 mm³). Splenocytes prepared from these mice were analyzed by antibody staining and flow cytometry (F). Tumor size was measured at the indicated time points (G). d, day. **, P < 0.01. Data are representative of two experiments.