FIG. 1.

CD40L stimulation level on the magnitude of human B-cell IgM AFC response. (A) Human CD19⁺ total B cells (1.5 × 10⁵ cell/culture) or (B) CD19⁺CD27⁻ naive B cells (1.5 × 10⁵ cell/culture) were cocultured with irradiated CD40L-L cells at indicated numbers per culture in the presence of recombinant human IL-2, IL-6, and IL-10 for 4 days and further cultured for an additional 3 days without CD40L-L cells. In both (A) and (B), cells were harvested on day 7 to enumerate IgM-secreting cells by ELISPOT. The cell number was determined by a particle counter, and the cell viability was assessed using a pronase activity assay. These data are representative of two separate experiments with at least four replicates per group. Data in panels (A) and (B) were obtained using total or naive B cells from two different donors in two separate experiments. The error bars indicate SE calculated for replicates of each treatment group.