SUMMARYBisphenol A (BPA) and p-nonylphenol (NP) are representative endocrine disruptors (EDs) that may have adverse effects on human health. The in¯uence of these compounds on allergic immune responses remains unclear. In this study, we have examined the effects of BPA and NP on production of interleukin-4 (IL-4), a pro-in¯ammatory cytokine closely associated with allergic immune responses. Both BPA and NP signi®cantly enhanced IL-4 production in keyhole limpet haemocyanin (KLH)-primed CD4T cells in a concentration-dependent manner. Treatment with BPA or NP in vivo resulted in signi®cant increase of IL-4 production in CD4T cells and of antigen-speci®c immunoglobulin E (IgE) levels in the sera of KLH-primed mice. Furthermore, BPA and NP enhanced the activation of IL-4 gene promoter in EL4 T cells transiently transfected with IL-4 promoter/reporter constructs, and the enhancing effect mapped to a region in the IL-4 promoter containing binding sites for nuclear factor (NF)-AT. Activation of T lymphocytes by phorbol 12-myristate 13-acetate/ionomycin resulted in markedly enhanced binding activities to the NF-AT site, which signi®cantly increased upon addition of BPA or NP, as demonstrated by the electrophoretic mobility shift assay, indicating that the transcription factor NF-AT was involved in the enhancing effect of BPA and NP on IL-4 production. The enhancement of IL-4 production by BPA or NP was signi®cantly reduced by nitrendipine, a blocker of Ca 2 in¯ux, and by FK506, a calcineurin inhibitor. FK506 inhibited the NF-AT±DNA binding activity and IL-4 gene promoter activity enhanced by BPA or NP. These results represent the ®rst report describing possible enhancement of allergic response by EDs through increasing IL-4 production in CD4T cells and antigen-speci®c IgE levels in the sera via the stimulation of Ca 2 /calcineurin-dependent NF-AT activation.