Native single-stranded B19 genome inhibits erythroid growth and down-regulates EPOR expression. (A) Purification of the B19 genome. B19 genome DNA was extracted from the virions. An equal molar ratio of plus and minus strands were then annealed and analyzed by agarose gel electrophoresis (arrow) and compared with molecular size markers (M). (B) Effects of B19 genome on erythroid growth. Purified CD34⁺ cells were cultured in erythroid medium with or without native single-stranded B19 genome DNA, dsDNA, and ssDNA derived from UT7/Epo-S1 cells. After 7 days in culture, the generated cells were collected, washed, and counted. Data are mean ± SD of 3 triplicates. (C-D) B19 down-regulated EPOR expression. Purified CD34⁺ cells were cultured for 4 days in erythroid medium, the cells harvested, and then incubated with serum containing B19. The cells were then cultured in erythroid medium. At the indicated days, the cells were harvested and EPOR expression on GPA⁺ cells analyzed using fluorocytometry. Data are representative of 3 independent experiments (C) and are mean ± SD (D). *P < .05. ***P < .001. NS indicates no significance.