Evidence that 8-methoxypsoralen (8-MOP) is a T-lymphocyte immunomodulatory agent

This study was designed to characterize the effects of the anti-psoriatic compound 8-methoxypsoralen (8-MOP) on human lymphocyte function in vitro. Normal human peripheral blood mononuclear cells were stimulated with an optimal (1%) or a suboptimal (0.05%) concentration of phytohemagglutinin (PHA). At the optimal concentration of PHA, 8-MOP (140 microM) caused a delay in lymphocyte proliferation, interleukin-2 (IL-2) production/accumulation and IL-2 receptor expression. Addition of exogenous IL-2 to cultures stimulated with an optimal concentration of PHA did not overcome the delay of lymphocyte proliferation and IL-2 receptor expression. At the suboptimal concentration of PHA, 8-MOP (140 microM) caused a sustained inhibition of lymphocyte proliferation, IL-2 production/accumulation and IL-2 receptor expression. Addition of exogenous IL-2 under these conditions restored the magnitude of lymphocyte proliferation and IL-2 receptor expression. However, the responses displayed the delayed lymphocyte proliferation and IL-2 receptor expression typical of cells incubated with 8-MOP and an optimal concentration of PHA.