Proliferation and differentiation of B henselae–infected HPCs. (A) Proliferation of HPCs upon infection with B henselae. Cells were seeded in 24-well plates and total numbers of cells were counted at days 1, 3, 6, and 9. *Significant difference compared with day 1 (P < .05). (B,C) Flow cytometric analysis of erythroid HPC differentiation. CD34 and GPA expression of uninfected and B henselae–infected HPCs (MOI 100) were determined by FACS analysis on day 1 and day 9 after infection. At each time point, 10 000 cells were analyzed. The number of CD34⁺ (HPCs) and GPA⁺ (erythroid) cells is expressed as a percentage of the total number of cells. All stainings were referred to isotype-matched control antibodies (see “Materials and methods”). Cells expressing CD34 or GPA, respectively, are given right of the dotted line (upper fluorescence limit of isotype control). (D,E) CD34 and GPA expression of uninfected and B henselae–infected HPCs on day 1 and day 9 after infection. The graphs show the means and standard deviations of the percentage of CD34⁺ (D) and GPA⁺ (E) cells obtained from 3 independent experiments.