Inhibition of T cell activation through down-regulation of TCR-CD3 expression mediated by an anti-CD90 Ab

Rhein attenuates lipopolysaccharide-primed inflammation through NF-κB inhibition in RAW264.7 cells: targeting the PPAR-γ signal pathway

Inflammation is a common inducer of numerous severe diseases such as sepsis. The NF-κB signaling pathway plays a key role in the inflammatory process. Its activation promotes the release of pro-inflammatory mediators like inducible nitric oxide synthase and tumor necrosis factor alpha. Peroxisome proliferator-activated receptor gamma (PPAR-γ) inactivates nuclear factor kappa B (NF-κB) and subsequently attenuates inflammation. Rhein, an agent isolated from rhubarb, has been known to have anti-inflammatory effects. However, its influence on PPAR-γ remains largely unknown. In this study, an inflammation model was constructed by stimulating RAW264.7 cells with lipopolysaccharide. Rhein was used as a therapeutic agent, while rosiglitazone (PPAR-γ activator) and GW9662 (PPAR-γ inhibitor) were used as disrupters for in depth studies. The results demonstrated that rhein inhibits NF-κB activation and inflammatory factor release. However, GW9662 significantly reduced this effect, indicating that PPAR-γ is a critical mediator in the rhein-mediated anti-inflammatory process. Additionally, positive modulation of PPAR-γ expression and activity by rosiglitazone correspondingly influenced the effects of rhein on inflammatory factors and NF-κB expression. We also found that rhein could enhance PPAR-γ, NF-κB, and histone deacetylase 3 (HDAC3) binding. These results indicate that rhein exerts its anti-inflammation function by regulating the PPAR-γ-NF-κB-HDAC3 axis.

Novel CD3-specific antibody induces immunosuppression via impaired phosphorylation of LAT and PLCγ1 following T-cell stimulation

The activation of T cells is known to be accompanied by the temporary downmodulation of the TCR/CD3 complex on the cell surface. Here, we established a novel monoclonal antibody, Dow2, that temporarily induces downmodulation of the TCR/CD3 complex in mouse CD4(+) T cells without activating T cells. Dow2 recognized the determinant on CD3ε; however, differences were observed in the binding mode between Dow2 and the agonistic anti-CD3ε Ab, 145-2C11. An injection of Dow2 in vivo resulted in T-cell anergy, and prolonged the survival of cardiac allografts without a marked increase in cytokine release. The phosphorylated forms of the signaling proteins PLC-γ1 and LAT in Dow2-induced anergic T cells were markedly decreased upon stimulation. However, the levels of phosphorylated LAT and PLCγ1 in Dow2-induced anergic T cells could be rescued in the presence of the proteasome inhibitor MG-132. These results suggest that proteasome-mediated degradation is involved in hypophosphorylated LAT and PLCγ1 in Dow2-induced anergic T cells. The novel CD3-specific Ab, Dow2, may provide us with a unique tool for inducing immunosuppression.

Modulation of the human T cell response by a novel non-mitogenic anti-CD3 antibody

The agonistic anti-human CD3ε antibody (Ab), OKT3, has been used to control acute transplant rejection. The in vivo administration of OKT3 was previously shown to induce the partial depletion of T cells and unresponsiveness (anergy) in the remaining CD4⁺ T cells. However, this therapy is also associated with the systemic release of several cytokines, which leads to a series of adverse side effects. We established a novel anti-human CD3ε Ab, 20-2b2, which recognized a close, but different determinant on the CD3ε molecule from that recognized by OKT3. 20-2b2 was non-mitogenic for human CD4⁺ T cells, could inhibit the activation of T cells in vitro, and induced T cell anergy in in vivo experiments using humanized mice. Cytokine release in humanized mice induced by the administration of 20-2b2 was significantly less than that induced by OKT3. Our results indicated that the CD3ε molecule is still an attractive, effective, and useful target for the modulation of T cell responses. The establishment of other Abs that recognize CD3ε, even though the determinant recognized by those Abs may be close to or different from that recognized by OKT3, may represent a novel approach for the development of safer Ab therapies using anti-CD3 Abs, in addition to the modification of OKT3 in terms of the induction of cytokine production.

T cells from autoimmune patients display reduced sensitivity to immunoregulation by mesenchymal stem cells: role of IL-2

Mesenchymal stem cells (MSCs) are multipotent progenitor cells which have been shown to possess broad immunoregulatory and anti-inflammatory capabilities, making them a promising tool to treat autoimmune diseases (AIDs). Nevertheless, as in recent years T cells from AID patients have been found to resist suppression by regulatory T cells, the question of whether they could be regulated by MSCs arises. To use MSCs as a therapeutic tool in human autoimmune diseases, one prerequisite is that T cells from autoimmune patients will be sensitive to these stem cells. The aim of this work was to investigate the ability of healthy donor derived MSCs to inhibit the proliferation of T cells from two pathophysiologically different AIDs: Multiple Sclerosis (MS) and Myasthenia Gravis (MG). We show that MSC-induced inhibition of interferon-γ production and surface expression of the CD3, CD4 and CD28 receptors by activated lymphocytes was similar in the AID patients and healthy controls. Contrarily, the MSCs' ability to suppress the proliferation of T cells of both diseases was significantly weaker compared to their ability to affect T cells of healthy individuals. Although we found that the inhibitory mechanism is mediated through CD14+ monocytes, the faulty cellular component is the patients' T cells. MSC-treated MS and MG lymphocytes were shown to produce significantly more IL-2 than healthy subjects while coupling of the MSC treatment with neutralizing IL-2 antibodies resulted in inhibition levels similar to those of the healthy controls. MSCs were also found to down-regulate the lymphocyte surface expression of the IL-2 receptor (CD25) through both transcription inhibition and induction of receptor shedding. Addition of IL-2 to MSC-inhibited lymphocytes restored proliferation thus suggesting a key role played by this cytokine in the inhibitory mechanism. Taken together, these results demonstrate the potential of a MSC-based cellular therapy for MS, MG and possibly other autoimmune diseases but also highlight the need for a better understanding of the underlying mechanisms for development and optimization of clinical protocols.

Impaired specific CD8 T cell response with aging is not due to decreased expression of CD90 on TCR transgenic T cells

BACKGROUND

CD90 (Thy-1) is a small glycoprotein that is particularly abundant on the surface of mouse thymocytes and peripheral T cells, and is often used as a marker in adoptive transfer experiments to distinguish donor and recipient T cells with different CD90 subtypes. We have performed adoptive transfer experiments with T cell receptor transgenic (TCR Tg) mice to study the impaired CD8 T cell response with aging.

FINDINGS

After stimulation with a CD8 T cell epitope, HA518-524, the response of TCR Tg CD8 T cells from aged mice was decreased compared to the response of TCR Tg T cells from young mice. CD90 expression was also substantially decreased on the TCR Tg CD8 T cells of aged mice. However, the responses of CD90hi and CD90low CD8 T cells of the aged mice were similar in both early activation and proliferation, demonstrating that the impaired Tg T cell response with aging is not associated with the altered CD90 expression on CD8 T cells.

CONCLUSIONS

The impaired Tg CD8 T cell response in aged mice is not due to age-associated changes in CD90 expression on Tg CD8 T cells.

Syndecan-2 can promote clearance of T-cell receptor/CD3 from the cell surface

T cells express the heparan sulphate proteoglycans syndecan-2 and syndecan-4. Syndecan-4 plays a T-cell inhibitory role; however, the function of syndecan-2 is unknown. In an attempt to examine this function, syndecan-2 was expressed constitutively in Jurkat T cells. Interestingly, the expression of syndecan-2 decreased the surface levels of T-cell receptor (TCR)/CD3 complex, concomitant with intracellular retention of CD3ε and partial degradation of the TCR-ζ chain. Immunofluorescence microscopy revealed that intracellular CD3ε co-located with Rab-4 endosomes. However, the intracellular pool of CD3ε did not recycle to the cell surface. The lower TCR/CD3 surface levels caused by syndecan-2 led to reduced TCR/CD3 responsiveness. We show that the cytosolic PDZ-binding domain of syndecan-2 is not necessary to elicit TCR/CD3 down-regulation. These results identify a previously unrecognized means of controlling surface TCR/CD3 expression by syndecan-2.