Figure 10.

Transfer of exosomes derived from primed B cells exposed to a β₂AR agonist directly enhance IgE production by recipient B cells. Donor supernatants: resting B cells were cultured as described in Figure 1 in the presence (black) or absence (grey) of terbutaline. Supernatants containing B cell-derived exosomes were removed after two days and the supernatant was fractionated by ultracentrifugation into exosome-intact and exosome-depleted components. Recipient B cells: resting B cells were cultured as described in Figure 1 in the absence of terbutaline. Whole, exosome-intact, or exosome-depleted supernatants were transferred in the presence of IL-4 (1 ng/ml) to recipient cells that were primed for 2 days in the absence of terbutaline and which had supernatants removed prior to donor supernatant transfers. (A) Supernatant fractions were transferred from donor cultures containing either WT (left panel) or β₂AR-deficient (right panel) B cells. IgE produced by recipient cells was measured by ELISA. Data are presented as mean IgE values (ng/ml) +/- SEM from one representative independent experiment of three from at least three replicate measurements. (B) Comparison of the number of recipient IgE-secreting cells (left panel) and the amount of IgE secreted by these cells (right panel) using the ELISPOT assay. Data are presented as the number of IgE-positive spots/well or as the fold change compared to whole supernatant transfer in IgE secreted on a per spot basis +/- SEM from one representative independent experiment of three from at least three replicate measurements. Significance is based on an unpaired t-test. *, p = .05, as compared to B cells exposed to fractions obtained from primed B cells alone.