Introduction

Monocytes and macrophages play key roles in cellular and humoral rejection after solid organ transplantation, but little is known about the effects of the immunosuppressive drugs tacrolimus and mycophenolic acid (MPA) on monocyte activation and function.

Patients, materials and methods

Blood samples from healthy volunteers (n=5) were spiked with 0, 10 50 or 200 ng/ml tacrolimus and 0 or 10 [mu]g/ml MPA, to determine the individual effects of these drugs on CD14+ monocytes, stimulated with PMA/ionomycin. Phosphorylation of the intracellular signaling proteins p38MAPK, ERK and Akt was measured with phospho-specific flowcytometry in peripheral blood monocytes. In addition, biological functions downstream of these signaling pathways were studied, including IL-1β production, phagocytosis and polarization into different types of activated macrophages (stimulated with IFN-γ, IL-4 and IL-10).

Results

Tacrolimus, only at 50 and 200 ng/ml, inhibited phosphorylation of p38MAPK (p < 0.05 and p < 0.01, respectively) more than p-Akt (p = 0.11 and p < 0.05, respectively) with a maximum of 35%. MPA, at a therapeutic concentration, showed the strongest inhibition of p-Akt (30%; p < 0.01). p-ERK was inhibited with a maximum of 15% after spiking with either 200 ng/ml tacrolimus or 10 [mu]g/ml MPA (p < 0.05 and p < 0.01, respectively).

The production of IL-1β by monocytes was not affected by tacrolimus, while MPA inhibited IL-1β production by 48% (p < 0.05). Phagocytosis by monocytes was not influenced by either drug. Monocyte/macrophage polarization was shifted to an M2-like phenotype in the presence of tacrolimus, seen as the increase in the M2 markers CD200R and CD16 (both p < 0.05).

Conclusions

Tacrolimus and MPA suppress monocyte signaling pathway activation only to a limited extent. The residual phosphorylation of signaling proteins probably explains the limited effect of both immunosuppressive drugs on cytokine production and phagocytosis, apart from monocyte differentiation. This suggests that innate immune responses mediated by monocytes after transplantation might still occur under immunosuppression.

CITATION INFORMATION: Kannegieter N, Hesselink D, Dieterich M, Kraaijeveld R, Rowshani A, Leenen P, Baan C. Tacrolimus and Mycophenolic Acid Have a Limited Inhibitory Effect on Monocyte Signaling Pathway Phosphorylation, Function and Differentiation. Am J Transplant. 2017;17 (suppl 3).

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