Interferon-␥ (IFN-␥

Interferon-gamma (IFN-gamma) is an immunoregulatory cytokine expressed in large granular lymphocytes and T cells. However, the molecular mechanisms underlying IFN-gamma gene transcription have not been fully defined. Here, we analyze the mechanisms responsible for the inhibition of IFN-gamma promoter activity by the glucocorticoid hormone dexamethasone. Cotransfection assays performed in Jurkat T cells demonstrated that the activity of the initial 108 base pairs of the IFN-gamma promoter was down-regulated in the presence of dexamethasone. Furthermore, utilizing electrophoretic mobility shift analysis, we identified activator protein 1 AP-1-cAMP response element binding protein-activating transcription factor (CREB-ATF) binding elements situated in positions of the IFN-gamma promoter previously identified as essential for promoter activity. Moreover, dominant negative mutants of the c-Jun proto-oncogene were able to mimic the same down-regulatory effect exerted by dexamethasone, and mutations that abolished the binding of the AP-1 CREB-ATF factors were able to block the glucocorticoid effect. These results suggest a model involving the inhibition of IFN-gamma AP-1 CREB-ATF DNA binding complexes as one of the mechanisms involved in the negative regulatory action of glucocorticoids on IFN-gamma gene expression and support the relevance of AP-1 CREB-ATF binding factors during the transcriptional activation of the IFN-gamma promoter in T cells.

Interleukin 2 (IL-2) administration is known to induce marked eosinophilia. To evaluate the potential role of eosinophils as anti-tumor effectors and to understand the direct or indirect effects of IL-2 on eosinophils, the physical and functional characteristics of eosinophils obtained during IL-2 therapy were compared with those of eosinophils obtained from the same patients before IL-2 administration, or from healthy donors. The treatment schedule consisted of subcutaneous (s.c.) injections of IL-2, and was performed in 7 patients with small-cell lung cancer (SCLC) in advanced stage. A marked increase of hypodense cells in peripheral blood was found to correlate with eosinophil activation in patients undergoing IL-2 therapy. Cytotoxic activity of eosinophils against allogeneic tumor cells (SCLC, K562 and melanoma lines), as assessed by direct and antibody (Ab)-dependent cellular cytotoxicity (ADCC), was markedly increased during IL-2 therapy. Conversely, eosinophils obtained before treatment, like those of healthy donors, lacked any activity against tumor cells. Sera from IL-2-treated, but not from untreated, patients, significantly improved the in vitro survival and anti-tumor cytotoxicity of eosinophils from healthy donors. Comparable effects were obtained with eosinophils cultured with interleukin 5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF) and, to a lesser extent, by tumor necrosis factor-alpha (TNF alpha), while no direct activity was mediated by IL-2. A 91% inhibition of eosinophil ADCC was found after pre-incubation of the sera of IL-2-treated patients with anti-IL-5 but not with anti-GM-CSF or anti-TNF alpha Ab. IL-5 mRNA expression was detected in peripheral-blood lymphocytes (PBL) obtained 4 hr after IL-2 injection during the second and third week of IL-2 therapy. Phenotypic analysis of eosinophils from IL-2-treated patients showed enhanced expression of activation markers, including Fc gamma RII (CD32), HLA-DR, CR3 (CD11b) and CRI (CD35). These findings suggest that a significant cytotoxicity against tumor cells can be mediated by eosinophils after indirect, IL-5-mediated in vivo activation by IL-2, and that eosinophils may be involved in the anti-tumor response(s) induced in vivo by IL-2.

Disregulation of vitamin A metabolism is able to generate different immunological effects, including altered response to infection, reduced IgG production, and differential regulation of cytokine gene expression (including interleukin-2 and -4 and interferon-gamma (IFN-gamma)). In particular, IFN-gamma gene expression is significantly affected by vitamin A and/or its derivatives (e.g. retinoic acid (RA)). Here, we analyze the effect of retinoic acid on IFN-gamma transcription. Transient transfection assays in the human T lymphoblastoid cell line Jurkat demonstrated that the activation of the IFN-gamma promoter was significantly down-regulated in the presence of RA. Surprisingly, two different AP-1/CREB-ATF-binding elements situated in the initial 108 base pairs of the IFN-gamma promoter and previously shown to be critical for transcriptional activity were unaffected by RA. Utilizing promoter deletions and electrophoretic mobility shift analysis, we identified a USF/EGR-1-binding element cooperating in the modulation of IFN-gamma promoter activity by RA. This element was found to be situated in a position of the IFN-gamma promoter close to a silencer element previously identified in our laboratory. These results suggest that direct modulation of IFN-gamma promoter activity is one of the possible mechanisms involved in the inhibitory effect of retinoids on IFN-gamma gene expression.