B cells secrete IL-10 in response to <i>B. microti</i> stimulation <i>in vitro</i>.

<p>Splenic B cells were purified from naïve or <i>B. microti</i>-infected mice by MACS as described in the <i>Materials and methods</i> (A) Representative histograms showing the purities of splenic CD19⁺ B cells isolated from either naïve (left) or <i>B. microti</i>-infected (right) mice. The purity of isolated B cells was >95% as assessed by flow cytometric analysis. (B) B cells sorted from naïve mice were stimulated with media alone, <i>B microti</i>, or LPS (1 µg/ml) for 24 h before the level of IL-10 in culture supernatants was determined by ELISA. (C) B cells isolated from either naïve mice or <i>B. microti</i>-infected mice were cultured with LPS for 5 h before the level of IL-10 in culture supernatants was measured by ELISA. (D) B cells were purified from naïve or <i>B. microti</i>-infected mice cultured with LPS for 5 h. The cells were then stained with anti-CD19 mAb, permeabilized, and stained intracellularly using anti-IL-10 mAb. Cytoplasmic IL-10 production was determined by flow cytometric analysis. Percentages indicate IL-10-producing cells among total CD19⁺ B cells. These <i>in vitro</i> experiments were repeated at least three times.