Cyclosporin A Inhibits a Discrete Step in T‐Lymphocyte Stimulation

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Abstract
Cyclosporin A (CyA) interferes with immune responses and prevents growth Factor release by stimulated T cells. However, it is not known whether this is due to an effect on the accessory cells, required for T‐cell responses, whether antigen recognition cannot occur, or whether later steps, leading to lymphokine production, are blocked. For this reason, the effect of CyA on homogeneous populations of T tumour cells was investigated. The immunosuppressive compound efficiently prevented T‐cell growth factor (TCGF) (interleukin 2) release by stimulated tumour cells. Still, the cells retained the surface antigen T3, known to be involved in T‐cell stimulation, after treatment with CyA. Furthermore, CyA failed to affect the inhibition of proliferation, observed in a T‐cell tumour in response to stimulation, indicating that the cells had received the stimulatory impetus. TCGF release, induced by treatment with a phorbol ester, was only partly sensitive to inhibition by CyA, demonstrating that CyA will interfere with discrete aspects of the stimulation of a T‐cell.