Evidence that calcineurin is rate-limiting for primary human lymphocyte activation.

Abstract

Cyclosporine (CsA) is both a clinical immunosuppressive drug and a probe to dissect intracellular signaling pathways. In vitro, CsA inhibits lymphocyte gene activation by inhibiting the phosphatase activity of calcineurin (CN). In clinical use, CsA treatment inhibits 50-75% of CN activity in circulating leukocytes. We modeled this degree of CN inhibition in primary human leukocytes in vitro in order to study the effect of partial CN inhibition on the downstream signaling events that lead to gene activation. In CsA-treated leukocytes stimulated by calcium ionophore, the degree of reduction in CN activity was accompanied by a similar degree of inhibition of each event tested: dephosphorylation of nuclear factor of activated T cell proteins, nuclear DNA binding, activation of a transfected reporter gene construct, IFN-␥ and IL-2 mRNA accumulation, and IFN-␥ production. Furthermore, the degree of CN inhibition was reflected by a similar degree of reduction in lymphocyte proliferation and IFN-␥ production in the allogeneic mixed lymphocyte cultures. These data support the conclusion that CN activity is rate-limiting for the activation of primary human T lymphocytes. Thus, the reduction of CN activity observed in CsA-treated patients is accompanied by a similar degree of reduction in lymphocyte gene activation, and accounts for the immunosuppression observed. ( J. Clin. Invest. 1997.

Pressure Overload Induces Severe Hypertrophy in Mice Treated With Cyclosporine, an Inhibitor of Calcineurin

“…Cyclosporine treatment results in partial, not complete, suppression of measured calcineurin activity and downstream events of dephosphorylation of NFAT transcription factors and nuclear DNA binding. 16, 17 The team of Halloran has previously shown that higher concentrations of cyclosporine are required to partially inhibit tissue calcineurin activity in vivo than in vitro, and higher blood concentrations are required to achieve similar levels of suppression of tissue calcineurin activity levels in mice than in humans. 15,16 In the present study, the measured blood cyclosporine levels at both peak and nadir exceed the IC 50 for inhibition of tissue calcineurin activity in mice.…”

Leukocyte-Targeted Myocardial Contrast Echocardiography Can Assess the Degree of Acute Allograft Rejection in a Rat Cardiac Transplantation Model

“…15 Thus, both T cells and macrophages are involved in the process of acute rejection, 14 with mutual interactions. Although CsA, a calcineurin inhibitor, exerts its immunosuppressant actions primarily by inhibiting T cells, 17 CsA was found to be effective in macrophage activation syndrome, 16 probably because of their close relationship to T cells. In fact, there was a close correlation between macrophage cell counts and T-cell counts among the rats subjected to various doses of CsA in our study.…”

“…10,15 Agents that affect primarily T cells, 12 including CsA, 16,17 can also limit monocyte/macrophage infiltration. 10,16 Indeed, the extent of macrophage infiltration as assessed by MRI with a magnetic contrast agent targeted to those cells was shown to allow detection of acute cardiac rejection in rats.…”

Randomized, International Study of Cyclosporine Microemulsion Absorption Profiling in Renal Transplantation with Basiliximab Immunoprophylaxis

“…Studies in vitro have shown that blood concentrations during this time are closely related to critical biological events of lymphocyte activation, including the inhibition of calcineurin activity and IL-2 production (16)(17)(18). Recent in vivo studies have supported these observations, showing that the absorption profile of CsA is more closely related to rejection risk than is a single trough measurement (6,10,11,19,20).…”