Coculture of A20 cells with fibroblasts expressing CD40L upregulates antigen expression. A total of 10⁶ lymphoblastoid A20 cells were cocultured with 2 × 10⁵ fibroblasts expressing either the neo gene as a control (solid line) or CD40L (broken line). After 3 days of culture, A20 cells were examined for surface antigen expression using FACS analysis. (A) Shows upregulation of B7.1 and of MHC Class I and II, while (B) shows upregulation of FAS (left panel) with a consequent increase in A20 cell death on addition of the FAS-binding antibody Jo-2 (right panel).