Cytokine profile during the activation of T cells by B cells shows substantial amounts of Th1 cytokines but also high levels of B-cell–derived IL-10. Supernatants were taken from DC–T-cell and from B-cell–T-cell cocultures and analyzed for cytokines by ELISA. Cells were analyzed for intracellular cytokines by FACS at 48 hours of culture. (A) B cells induce substantial amounts of IL-2 in supernatants of B-cell–T-cell cocultures, but DCs are at least twice as powerful on a per-cell basis. Bars represent mean plus or minus SD. (B) While equivalent amounts of IFNγ can be observed in supernatants of DC–T-cell and B-cell–T-cell cocultures, a marked increase in the amount of IL-10 is found in cultures containing B cells. (C) Intracellular cytokine staining reveals that IL-10 is produced by the CD4 negative population. The level of induced IL-4 is low for all cells. (D) Costaining with the specific B-cell marker CD19 identifies B cells as the source of IL-10. The data shown are representative of 3 independent experiments.