CD4+T Cells Reactivated with Superantigen Are both More Sensitive to FasL-Mediated Killing and Express a Higher Level of FasL

The interaction between CD95 (Fas) and CD95L (Fas ligand) initiates apoptosis in a variety of cell types. Although the regulation of CD95L expression on activated T cells is an area of intense study, knowledge related to the induction of CD95L promoter activity in primary T cells is lacking. In this report we describe the generation of a novel transgenic mouse strain, CD95LP-Luc, in which murine CD95L promoter sequence controls the expression of a luciferase reporter gene. We use these mice to illustrate several important findings related to transcriptional regulation of CD95L in primary T cells. We demonstrate that maximal CD95L promoter activity occurs only after prolonged T cell stimulation and requires costimulation through CD28. We provide evidence that thymocytes express CD95L/luciferase after strong TCR ligation and that inducible CD95L promoter activation is present, but unequal, in both Th1 and Th2 effector cells. We also illustrate that while agonist peptide presentation by APCs generates robust proliferation during a primary T cell response, the same stimulus induces only modest CD95L promoter activity. These results suggest alternate explanations for the well-characterized delay in CD95-mediated activation-induced cell death following initial ligation of the TCR.

Section: Discussionsupporting

confidence: 60%

mentioning

confidence: 99%

The Regulation of CD95 (Fas) Ligand Expression in Primary T Cells: Induction of Promoter Activation in CD95LP-Luc Transgenic Mice

Norian¹,

Latinis²,

Eliason³

et al. 2000

“…6, T cells from the spleen or colon that were activated with SEB could induce death and DNA degradation in Mode-K cells. Because SEB induces the expression of FasL on T cells (43), it is possible that apoptosis of epithelial cells was mediated by interactions between Fas and FasL. This model is supported by the results of other studies documenting the expression of Fas on epithelial cells and FasL by intestinal T cells in graft-vs-host disease (54,55).…”

Section: Figuresupporting

confidence: 54%

“…As activated T cells may express only modest amounts of class II MHC, the T cells are not capable of long term expansion in the absence of feeder cells. Moreover, because SEB induces the expression of FasL on T cells, it is likely that, in time, activation will lead to a negative selection of the T cells as they die due to Fas/FasL interactions (43). The magnitude of the proliferative responses varied among strains of mice, but they were present in all strains tested.…”

Section: Discussionmentioning

confidence: 99%

Staphylococcal Enterotoxin B Stimulates Expansion of Autoreactive T Cells That Induce Apoptosis in Intestinal Epithelial Cells: Regulation of Autoreactive Responses by IL-10

Ito

Takaishi

Jin

et al. 2000

T cell responses to self Ags and normal microbial flora are carefully regulated to prevent autoreactivity. Because IL-10-deficient mice develop colitis, and this response is triggered by luminal flora, we investigated whether IL-10 regulates the ability of microbial Ags to induce autoreactive T cells that could contribute to intestinal inflammation. T cells from wild-type mice were primed with staphylococcal enterotoxin B (SEB) in vitro, which induced an autoreactive proliferative response to syngeneic feeder cells. The cells were predominately CD3+ and CD4+. T cells from IL-10-deficient mice were constitutively autoreactive, and SEB priming enhanced this further. The autoreactive, proliferative response of T cells from wild-type mice was suppressed by IL-10 in the primary or secondary culture, and this effect was inhibited by neutralizing Abs to the IL-10R. To confirm that an autoreactive repertoire was expanded after SEB priming, we used CBA/J mice (Mls-1a) in which autoreactive T cells recognizing the endogenous viral superantigen are depleted (Vβ6, 7, 8.1 TCR-bearing cells). However, SEB rescued these autoreactive T cell repertoires. Adding anti-MHC class II Ab blocked the autoreactive response. SEB-primed splenic or colonic T cells also induced apoptosis in syngeneic intestinal epithelial cells that was blocked significantly by IL-10. Thus, microbial Ags have the potential to abrogate self tolerance by stimulating autoreactive T cells that become cytolytic to target cells. IL-10 plays a protective role in maintaining self tolerance after microbial stimulation by preventing the activation of T cells that contribute to epithelial cell damage.

“…MRL-lpr/gld double-mutant mice were bred at the Boston University School of Medicine animal facility (15).…”

Section: Micementioning

confidence: 99%

Fas Ligand Engagement of Resident Peritoneal Macrophages In Vivo Induces Apoptosis and the Production of Neutrophil Chemotactic Factors

Hohlbaum

Gregory

et al. 2001

Self Cite

141

149

Fas ligand (FasL) is a potent proapoptotic type-II transmembrane protein that can cause cell death in Fas+ target populations. Despite the presumed “silent” nature of apoptotic cell death, forced expression of FasL can induce a dramatic inflammatory response. To elucidate the in vivo mechanism(s) linking FasL and inflammation, we used a membrane-bound cell-free form of FasL (mFasL-vesicle preparation (VP)). We found that i.p. injection of FasL-microvesicles led to the rapid activation and subsequent demise of Mac1high resident peritoneal macrophages. Apoptosis of Mac1high peritoneal macrophages was observed within 0.5 h of mFasL-VP injection and correlated with the detection of increased macrophage inflammatory protein (MIP)-2 levels in peritoneal lavage fluid as well as induced RNA expression of IL-1β, MIP-2, MIP-1α, and MIP-1β. In vitro culture of purified peritoneal populations identified Mac1high cells as the major cytokine/chemokine producers in response to mFasL-VP. Purified Mac1high cells exposed to FasL could restore the ability of Fas-deficient mice to mount an inflammatory response. Our data demonstrate that the FasL-mediated inflammatory response starts with the production of proinflammatory mediators by preapoptotic resident tissue macrophages and suggest a general mechanism responsible for neutrophil inflammation seen in cases of FasL-expressing allografts.