Hyperinducible expression of the interferon-gamma (IFN-γ) gene and its suppression in systemic lupus erythematosus (SLE)

Transient expression of IFN-γ and IL-2 mRNA and its control by post-transcriptional and suppressive mechanisms were analysed in phytohaemagglutinin-induced peripheral blood mononuclear cells (PBMC) from 47 patients with SLE and 31 age-matched normal donors, using quantitative hybridization with antisense RNA probes. In SLE, basal levels of gene expression did not deviate from those of normal donors, but strongly aberrant patterns were obtained upon induction. The ratio of subjects exhibiting highly inducible IFN-γ gene expression in their PBMC to those showing moderate or low inducibility was increased five-fold in SLE (P = 0.003). High inducibility was observed for 43% of SLE patients and was equally pronounced in partial remission, mild or active disease. Inducibility of IL-2 mRNA, by contrast, remained similar to that for normal donors. However, regulation of IFN-γ gene expression differed for mild SLE. Patients with mild disease showing high inducibility of IFN-γ mRNA in their PBMC not only had the highest frequency of responders, but also the highest extent of an individual response, defined by superinduction of mRNA to agents that relieve suppression (γ-irradiation) or post-transcriptional down-regulation (cycloheximide). By contrast, patients with active SLE showing high IFN-γ mRNA inducibility had normal suppressive capacity as well as posttranscriptional control. Hence, both high inducibility of the IFN-γ gene and its suppression are relevant to disease. Hyperactivation of the IFN-γ gene may be alleviated in mild SLE by a vigorous, concomitant activation of post-transcriptional control and of cell-mediated suppression.