Natural Human Interferon-α Augments Apoptosis in Activated T Cell Line

We have previously shown that interferon-α (IFN-α) augments interleukin-2 (IL-2) production in mitogen-activated but not unstimulated T cells (1). Here, we studied the effect of IFN-α on activation-driven cell death (apoptosis) using a human leukemia T cell line, MOLT-16, as a T cell activation model. IFN-α alone had no effect on either the IL-2 production or apoptosis of MOLT-16 cells, but significantly increased both the IL-2 production and apoptosis in the MOLT-16 cells after phytohemagglutinin (PHA) stimulation as determined by CTLL-2 assay and by flow cytometric analysis using propidium iodide (PI) staining. Since IL-2 has been shown to induce apoptosis in some systems, we next evaluated whether the apoptosis in MOLT-16 cells was due to endogenous IL-2 production upon PHA stimulation. However, the addition of exogenous IL-2 to unstimulated cultures of MOLT-16 did not induce DNA fragmentation, a characteristic feature of apoptosis, as determined by DNA electrophoresis and by flow cytometric analysis with PI-stained cells. Furthermore, anti-IL-2 antibody did not prevent PHA-induced DNA fragmentation in MOLT-16 cells. Thus, we conclude that both PHA-induced IL-2 production and apoptosis are outcomes of T cell activation and that IFN-α may exert immunoregulatory effects on T cell activation by augmenting both processes.