Response of ICF B cells to BCR stimulation and CD40 cross-linking. Flow cytometry analysis of PBMCs from a healthy child (HD) and patient P1 stained with anti-CD19, anti-CD69, anti-CD86, and anti-CD27, gated on CD19⁺ cells at time zero or after 20 hours' stimulation. Numbers in brackets indicate the percentage of strained cells within the CD19⁺ cells. Cells were stimulated by coculture with irradiated hCD40L-transfected fibroblasts in the presence of F(ab) antihuman μ, rIL-2, and rIL-10. P1 data are representative of P1, P3, and P4; HD data are representative of 3 healthy children.