IMMUNOLOGICAL STUDIES ON RENAL TRANSPLANTATION

IV. Studies on the Mode of Action of Cyclosporin A

Abstract

Immunosuppressive mechanism of cyclosporin A (CsA) was studied using human lymphocytes in vitro. MLC was performed by responder cells cultured together with mitomycin treated stimulator cells for five days. Twenty hours before harvesting, ³H-TdR was added and its uptake was counted. CML was assayed by incubating effector cells from MLC for four hours with 3-day-old PHA stimulated target cells labeled with ⁵¹Cr (E/T=50/1).
A delay in adding CsA to the allogenic MLC resulted in a progressive increase of ³H-TdR uptake and when added over 48 hours after the beginning of MLC, inhibition rate was low. On the contrary, removing CsA from the culture after 24 hours showed relatively strong inhibition. These results suggest that CsA acts at an early stage of lymphocyte stimulation. Although MLC performed in the absence of CsA resulted in the generation of specific cytotoxic effector cells, when CsA was added in the effector phase, it had no inhibitory effect on the action of cytotoxic T lymphocytes.
CsA was assessed for its effect on the production of interleukin 2 (IL 2) and the acquisition of responsiveness to IL 2. Supernatants from the CsA-treated MLC showed a dose-dependent decrease in the ability to support the proliferation of Con A stimulated lymphocytes, indicating the inhibitory effect of CsA on the production of IL 2. CsA showed a dose-dependent inhibition of MLC, but this inhibitory effect could not be reversed completely when exogenous IL 2 was added to the culture. When lymphocytes were stimulated by IL 2 after preincubation with Con A and/or CsA, proliferative activity of lymphocytes was reduced in the presence of CsA during the preincubation.
From the above results, it is concluded that CsA inhibits T cell activation both by blocking IL 2 production as well as by inhibiting the induction of IL 2 responsiveness.