Despite the fact that the negative regulatory element (NRE) within the upstream regulatory region of human IL-2 receptor alpha (IL-2Ralpha) gene has been identified two decades ago, mechanisms of the NRE function on the gene are hitherto unknown. In this paper, we report for the first time that the immunoglobulin transcription factor 2B (ITF2B) encoded by transcription factor 4 (TCF4) gene is a NRE binding protein. The full-length TCF4 cDNA clone was obtained from a HTLV-1 transformed human peripheral T cell MACHERMAKER cDNA library with NRE as the bait in yeast one-hybrid system. The NRE binding ability of ITF2B was further confirmed in chromatin-immunoprecipitation assay. Competitive RT-PCR-based promoter activity assay showed that over-expression of ITF2B protein inhibited the expression of IL-2Ralpha gene in Jurkat cells in an NRE-dependent manner. The function of ITF2B on the inhibition of both the IL-2Ralpha and the 5'LTR activity of HIV-1 shed light on the essence of NRE binding protein as a potential target for immune therapy and treatment in AIDS patients.