Related Experiment Videos
Low-dose immunosuppression by cyclosporine operating via antigen-presenting dendritic cells
1Antigen Presentation Research Group, MRC Clinical Research Centre, Harrow, England.
Insights
Cyclosporine (CsA) significantly inhibits lymphocyte proliferation at very low doses, particularly when acting on antigen-presenting dendritic cells (DC). This low-dose effect complements known high-dose inhibition, revealing a biphasic action of CsA on immune cells.
Area of Science:
- Immunology
- Pharmacology
Background:
- Cyclosporine (CsA) is a well-known immunosuppressant.
- Its primary mechanism involves inhibiting T-cell activation.
- The dose-response and cellular targets of CsA require further elucidation.
Purpose of the Study:
- To investigate the inhibitory effects of CsA on lymphocyte proliferation.
- To determine the dose-dependent and time-dependent effects of CsA on T cells and antigen-presenting cells.
- To identify novel mechanisms of CsA action.
Main Methods:
- Utilized hanging drop cultures to assess lymphocyte stimulation.
- Stimulated lymphocytes using concanavalin A and allogeneic dendritic cells (DC) in mixed leukocyte cultures (MLC).
- Investigated CsA effects by pulsing T cells and DC separately with the drug before MLC.
Main Results:
- Significant lymphocyte proliferation inhibition observed at low CsA concentrations (10(-9)-10(-7) µg/ml), in addition to high-dose inhibition.
- Intermediate CsA doses showed minimal inhibition.
- Pulsing DC with CsA revealed biphasic inhibition, dependent on pretreatment time and drug concentration, suggesting a dual effect on antigen-presenting cells.
Conclusions:
- CsA exhibits a biphasic inhibitory effect on lymphocyte proliferation, acting on both T cells and antigen-presenting cells.
- A novel low-dose inhibition mechanism mediated by dendritic cells was identified.
- These findings expand the understanding of CsA's complex immunomodulatory actions.
Abstract:
The inhibitory effect of cyclosporine on the stimulation of lymphocytes was tested in 20 microliters hanging drop cultures. Cells were stimulated by concanavalin A, or by allogeneic dendritic cells in a mixed leukocyte culture (MLC). Significant inhibition of lymphocyte proliferation was obtained with low concentrations of CsA (10(-9)-10(-7) micrograms/ml) in addition to the well-documented, dose-dependent inhibition at concentrations greater than or equal to 10(-1) micrograms/ml. Intermediate doses (10(-6)-10(-2) micrograms/ml) caused little inhibition. To establish whether the CsA was acting on the antigen-presenting cells or on the responding T cells, each population was pulsed with CsA before adding to the MLC. Higher doses of CsA were required to cause inhibition using this short-term pretreatment rather than continuous presence of CsA; however, when DC were pulsed with CsA, biphasic effects of the drug were seen. The time of DC pretreatment with 1 microgram/ml CsA was varied, and inhibition was seen after 1-3 hr and 16-24 hr pretreatment but not at intermediate time points. Similarly, a biphasic dose-response developed when DC-pretreatment time was fixed (2 hr) and drug concentration was varied. By contrast, on pulsing responder lymphocytes with CsA there was a biphasic effect in some experiments, but more often a single dose-dependent inhibition occurred, particularly when DC were removed from the responder cells. Major dose-dependent inhibitory effects of CsA may therefore act on both antigen-presenting DC and on lymphocytes, but this work reveals an additional low-dose inhibition that can operate via DC.