Tacrolimus Inhibits NF-κB Activation in Peripheral Human T Cells

The calcineurin inhibitor, tacrolimus (TAC), inhibits the protein phosphatase activity of calcineurin, leading to suppression of the nuclear translocation of NFAT and inhibition of T cell activation. Apart from NFAT also the transcription factor NF-kappa B plays a key functional role in T cell activation. Therefore, blockade of the NF-kappa B activation cascade by immunosuppressive drugs prevents immune activation. Here we studied whether TAC blocks NF-kappa B activation in peripheral human T cells. After anti-CD3/CD28-activation of T cells from healthy volunteers, NF-kappa B (p65) phosphorylation was measured by flow cytometry in CD3+ T cells, CD4+ helper T cells and CD8+ cytotoxic T cells in the absence and presence of TAC 10 mu g/mL, sotrastaurin 500 nM (positive control) and mycophenolic acid 10 mg/mL (negative control; n = 6). NF-kappa B transcriptional activity was measured by ELISA and intracellular TNF alpha protein, a downstream target, was measured by flow cytometry to assess the functional consequences of NF-kappa B blockade. Anti-CD3/28-activation induced NF-kappa B phosphorylation in CD3+ T cells, CD4+ T cells and CD8+ T cells by 34% (mean), 38% and 30% resp. (p <0.01). Sotrastaurin inhibited NF-kappa B activation in the respective T cell subsets by 93%, 95% and 86% (p <0.01 vs. no drug), while mycophenolic acid did not affect this activation pathway. Surprisingly, TAC also inhibited NF-kappa B phosphorylation, by 55% (p < 0.01) in CD3+ T cells, by 56% (p < 0.01) in CD4+ T cells and by 51% in CD8+ T cells (p <0.01). In addition, TAC suppressed NF-kappa B DNA binding capacity by 55% (p < 0.05) in CD3+ T cells and TNF alpha protein expression was inhibited in CD3+ T cells, CD4+ T cells and CD8+ T cells by 76%, 71% and 93% resp. (p <0.01 vs. no drug), confirming impaired NF-kappa B signaling. This study shows the suppressive effect of TAC on NF-kappa B signaling in peripheral human T cell subsets, measured at three specific positions in the NF-kappa B activation cascade.