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NF‐κB is involved in the regulation of CD154 (CD40 ligand) expression in primary human T cells

Cognate interactions between CD154 (CD40 ligand, CD40L) on activated T cells and its receptor CD40 on various antigen‐presenting cells are involved in thymus‐dependent humoral immune responses and multiple other cell‐mediated immune responses. We have studied the regulation of CD154 expression in human T cells after activation with anti‐CD3 and anti‐CD28 antibodies or after pharmacological activation of protein kinase C with phorbol 12‐myristate 13‐acetate, and the calcium ionophore ionomycin. Under these conditions, transcription of the CD154 gene was rapidly induced without requiring de novo protein synthesis. Pharmacological inhibitors of NF‐κB activation down‐regulated CD154 mRNA and protein levels. Cyclosporin A, an inhibitor of NF‐AT activation, acted similarly, and the effects of both inhibitors were additive. A potential NF‐κB binding site is present within the CD154 promoter at positions −1190 to − 1181. In electrophoretic mobility shift assays, this sequence was specifically bound by NF‐κB present in nuclear extracts from activated T cells. Furthermore, in transient co‐transfection of Jurkat T cells, p65 activated the transcription of a reporter construct containing a multimer of this NF‐κB binding site. These observations demonstrate a role of NF‐κB transcription factors in the regulation of CD40L expression in activated primary human T cells.