Background: The calcineurin-inhibitor, tacrolimus (TAC), inhibits the protein-phosphatase-activity of calcineurin, leading to suppression of the nuclear translocation of NFAT and subsequent T-cell activation. Apart from NFAT also the transcription factor NF-ΚB plays a key functional role in T-cell activation. Therefore, blockade of the NF-ΚB activation cascade by immunosuppressive drugs prevents immune activation. Here we studied whether TAC blocks NF-ΚB activation in primary human T-cells.

Methods: After anti-CD3/CD28-activation of CD3+ T-cells from healthy volunteers (n=6), NF-ΚB phosphorylation (p65, S529) was measured by flow cytometry in CD3+, CD4+ and CD8+ T-cells in the absence and presence of TAC 10 ng/mL, sotrastaurin 500nM (positive control); and mycophenolic acid 10 Μg/mL (negative control). Intracellular TNFa protein, the downstream target of NF-ΚB, was measured by flow cytometry in the T-cell subsets to assess the functional consequences of NF-ΚB blockade.

Results: Anti-CD3/28-activation induced NF-ΚB phosphorylation in 34% (95% CI: 31-37%), 38% (95% CI: 33-42%) and 30% (95% CI:26-35%) of CD3+, CD4+ and CD8+ T-cells respectively. Sotrastaurin inhibited NF-ΚB activation in CD3+ T-cells by 93% (p<0.01 vs. no drug), in CD4+ T-cells by 95% (p<0.01) and in CD8+ T-cells by 86% (p<0.01), while mycophenolic acid did not affect this activation pathway. Surprisingly, TAC 10 ng/mL also inhibited NF-ΚB phosphorylation, by 52% (p<0.01) in CD3+ T-cells, by 54% (p<0.01) in CD4+ T-cells; and by 45 % in CD8+ T-cells (p<0.01). Moreover, TAC also suppressed TNFa protein expression, by 71% (p<0.01 vs. no drug), 64% (p<0.01) and 90% (p<0.01) in CD3+, CD4+ and CD8+ T-cells, respectively, confirming impaired NF-ΚB signaling.

Conclusions: This study shows the novel suppressive effect of TAC on the NF-ΚB activation pathway and its responsive effector molecules in T cells. Hence, TAC is more than a calcineurin inhibitor.

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