A20.2J and HOIP-deficient cells transduced with an empty retroviral vector (A20.2J + pMIP and HOIP-/- + pMIP, respectively), or HOIP-deficient cells transduced with a HOIP-encoding retrovirus (HOIP-/- + HOIP) were cultured overnight with agonistic anti-CD40 or an isotype control antibody (iso), with or without IL-4.