The activated T cell-attracting CC chemokine CCL22 is expressed by stimulated B cells and mature dendritic cells (DC). We have cloned and sequenced the complete mouse gene, including 4 kb of the 5'-flanking promoter region, and detected two distinct sites for initiation of transcription by 5'-RACE. Reporter gene assays indicate that the promoter reflects the specificity of the endogenous gene. Within the proximal promoter region, we identified potential binding sites for NF-kappaB, Ikaros, and a putative GC box. All three regions bind proteins. The NF-kappaB site was shown to specifically bind NF-kappaB subunits p50 and p65 from nuclear extracts of LPS-stimulated B cells, B cell line A20/2J, TNF-alpha-stimulated bone marrow-derived DC, and DC line XS106. Furthermore, promoter activity was affected by targeted mutagenesis of the NF-kappaB site and transactivation with p50 and p65. The region harboring the putative Ikaros site contributes to promoter activity, but the binding protein does not belong to the Ikaros family. The GC box was shown to specifically bind Sp1 using extracts from LPS-stimulated B cells and A20/2J but not from DC and DC line XS106. Additionally, Sp1 transactivated the promoter in A20/2J but not in XS106 cells, and mutation of the Sp1 site diminished transactivation. Furthermore, binding of the protein complex at the GC box is required for NF-kappaB activity, and the spatial alignment of the binding sites is of critical importance for promoter activity. Thus, identical and distinct proteins contribute to expression of CCL22 in DC and B cells.