Related Experiment Video
Updated: Jul 13, 2026
Isolation and Activation of Murine Lymphocytes
Published on: October 30, 2016
Evidence that calcineurin is rate-limiting for primary human lymphocyte activation
T D Batiuk1, L Kung, P F Halloran
1Department of Medicine, Division of Nephrology and Immunology, University of Alberta, Edmonton, Alberta AB T6G 2R8, Canada. tbatiuk@mdep.iupui.edu
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-gamma and IL-2 mRNA accumulation, and IFN-gamma production. Furthermore, the degree of CN inhibition was reflected by a similar degree of reduction in lymphocyte proliferation and IFN-gamma 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.
Insights
Cyclosporine (CsA) partially inhibits calcineurin (CN) activity, a key enzyme in T lymphocyte activation. This partial inhibition significantly reduces T cell proliferation and immune responses, explaining CsA
Area of Science:
- Immunology
- Molecular Biology
- Pharmacology
Background:
- Cyclosporine (CsA) is a widely used immunosuppressive drug.
- CsA functions by inhibiting the phosphatase activity of calcineurin (CN).
- In clinical settings, CsA reduces CN activity in leukocytes by 50-75%.
Purpose of the Study:
- To investigate the impact of partial calcineurin inhibition on T lymphocyte signaling and activation.
- To model the in vivo level of CN inhibition in vitro using primary human leukocytes.
Main Methods:
- Primary human leukocytes were treated with CsA to achieve partial CN inhibition.
- Cells were stimulated with calcium ionophore to assess downstream signaling events.
- Key events measured included dephosphorylation of NFAT, DNA binding, reporter gene activation, cytokine mRNA accumulation (IFN-gamma, IL-2), and protein production.
- Lymphocyte proliferation and IFN-gamma production were assessed in allogeneic mixed lymphocyte cultures.
Main Results:
- Partial CN inhibition by CsA led to a proportional reduction in all tested downstream signaling events.
- Dephosphorylation of nuclear factor of activated T cell (NFAT) proteins was significantly inhibited.
- IFN-gamma and IL-2 mRNA accumulation and IFN-gamma production were reduced in a dose-dependent manner.
- Lymphocyte proliferation and IFN-gamma production were decreased in mixed lymphocyte cultures.
Conclusions:
- Calcineurin activity is rate-limiting for the activation of primary human T lymphocytes.
- The observed reduction in CN activity in CsA-treated patients directly correlates with decreased lymphocyte gene activation.
- This correlation explains the immunosuppressive effects of CsA in clinical use.
