Regulation der Immunantwort durch CREMalpha

Systemic lupus erythematosus (SLE) is a fatal autoimmune disease which affects nearly all organs in the human body. Despite the severity of disease treatment options are scarce apart from immune suppression. T cells are critical players in SLE. One factor which contributes to T cell pathophysiology in SLE is an enhanced expression of the cAMP response element modulator (CREM)alpha, a transcription factor, which contributes to several abnormalities in these cells. In my thesis I analyzed the role of CREMalpha in T cells in vitro and in vivo. To explore the relevance of CREMalph in vivo in a lupus setting we crossed CD95 (fas) knock-out mice into mice which overexpress CREM in T cells (fas-/- CREM TG). The CREM TG fas-/- CREM TG mice mice suffered from severely accelerated lymphadenopathy and splenomegaly much earlier in life than wildtype fas-/- animals. Lymphadenopathy and splenomegaly was caused by a massively enhanced expansion of double negative T cells (CD3+CD4-CD8-, DNTs), a reduction of regulatory T cells (Tregs), while amounts IL-17 and IL-21 secreting cells were increased compared to fas-/- mice without CREMalpha overexpression. To our knowledge this is the first report that overexpression of CREMalpha aggravates autoimmunity in vivo. We further analyzed the role of CREMalpha in regulatory T cells and Th17 cells in a CREM knock-out mouse model (CREM-/-) and in a mouse, which selectively overexpresses CREMalpha in T cells (CREM TG). When we generated inducible Tregs from naïve CD4+ T cells the overall expression of Foxp3+ T cells was higher in wildtype T cells than in CREM TG T cells. Vice versa the expression of inducible Tregs generated from CREM-/- mice was significantly higher than from wildtype mice. Furthermore, the knock-out of CREM enhanced the suppressive capacity of Tregs in mice in vitro in suppressionassays and in vivo in a mouse model of transfercolitis. Coimmunprecipitation experiments indicated that CREMalpha interacts with FOXP3 in Tregs. Furthermore microarray analyses identified several genes which might be regulated by CREMalpha in Tregs. We furthermore analysed the role of CREMalpha in Th17 cells in vitro and noticed enhanced development of Th17 cells in CREM TG mice while the fraction of IL-17 producing T cells was reduced in CREM-/- mice compared to wildtype mice. The functional relevance of the enhanced Th17 response in CREM TG mice was demonstrated by two in vivo colitis models. We detected an important mechanism of CREM driven IL-17 expression by mean of chip assays which revealed a CREM binding to the IL17a promotor. Summing up these data indicate a role of CREMalpha for the functionality of Tregs and Th17 cells in vitro and in vivo. We next asked if CREMalpha also influences follicular helper T cells (Tfhs) and B cell responses. CREMalpha enhanced the expression of Tfhs, germinal center(GC) B cells and led to increased serum levels of autoantibodies in fas-/- mice. Moreover CREM TG mice showed enhanced levels of follicular helper T cells, GC B cells and higher specific IgG levels in sera after immunization compared to wildtype mice. These experiments expand the role of CREMalpha as a transcription factor expressed in T cells, which significantly alters B cell response. This thesis confirms a pathogenic role of CREMalpha in vivo and provides evidence that the expression of CREMalpha in T cells of patients with SLE does not represent an epiphenomenon. Moreover CREMalpha might be a new transcription factor which is crucial for the regulation of Tregs, Th17 and Tfh cells. This work therefore contributes to the understanding of the complex transcription factor network in T cell subsets

Reactive Oxygen Species as Regulators of MDSC-Mediated Immune Suppression

Reactive oxygen species (ROS) molecules are implicated in signal transduction pathways and thereby control a range of biological activities. Immune cells are constantly confronted with ROS molecules under both physiologic and pathogenic conditions. Myeloid-derived suppressor cells (MDSCs) are immunosuppressive, immature myeloid cells and serve as major regulators of pathogenic and inflammatory immune responses. In addition to their own release of ROS, MDSCs often arise in oxidative-stress prone environments such as in tumors or during inflammation and infection. This evidently close relationship between MDSCs and ROS prompted us to summarize what is currently known about ROS signaling within MDSCs and to elucidate how MDSCs use ROS to modulate other immune cells. ROS not only activate anti-oxidative pathways but also induce transcriptional programs that regulate the fate and function of MDSCs. Furthermore, MDSCs release ROS molecules as part of a major mechanism to suppress T cell responses. Targeting redox-regulation of MDSCs thus presents a promising approach to cancer therapy and the role of redox-signaling in MDSCs in other disease states such as infection, inflammation and autoimmunity would appear to be well worth investigating