Investigations of dynamic amyloid-like structures of the Wnt signalling pathway by solid-state NMR

We report solid-state Nuclear Magnetic Resonance (ssNMR) studies on amyloid-like protein complexes formed by DIX domains that mediate key protein interactions in the Wnt signalling pathway. Our results provide insight into the 3D fold of the self-associated Axin-DIX domain and identify a potential lipid cofactor.

Deubiquitination of Dishevelled by Usp14 is required for Wnt signaling

Dishevelled (Dvl) is a key regulator of Wnt signaling both in the canonical and non-canonical pathways. Here we report the identification of a regulatory domain of ubiquitination (RDU) in the C-terminus of Dvl. Mutations in the RDU resulted in accumulation of polyubiquitinated forms of Dvl, which were mainly K63 linked. Small interfering RNA-based screening identified Usp14 as a mediator of Dvl deubiquitination. Genetic and chemical suppression of Usp14 activity caused an increase in Dvl polyubiquitination and significantly impaired downstream Wnt signaling. These data suggest that Usp14 functions as a positive regulator of the Wnt signaling pathway. Consistently, tissue microarray analysis of colon cancer revealed a strong correlation between the levels of Usp14 and β-catenin, which suggests an oncogenic role for Usp14 via enhancement of Wnt/β-catenin signaling.

Positive selection of an MHC class-I restricted TCR in the absence of classical MHC class I molecules

The H-2Ld alloreactive 2C T cell receptor (TCR) is commonly considered as being positively selected on the H-2Kb molecule. Surprisingly, 2C TCR+ CD8+ single-positive T cells emerge in massive numbers in fetal thymic organ culture originating from 2C transgenic, H-2KbD(b-/-) (2C+KbD(b-/-)) but not in fetal thymic organ culture from beta2-microglobulin(-/-) 2C transgenic animals. Mature CD8+ T cells are observed in newborn but not in adult 2C+KbD(b-/-) mice. These CD8+ T cells express the alpha4beta7 integrin, which allows them to populate the intestine, a pattern of migration visualized by intrathymic injection of FITC and subsequent accrual of FITC-labeled lymphocytes in the gut. We conclude that the 2C TCR is reactive not only with H-2Ld and H-2Kb, but also with nonclassical MHC class I products to enable positive selection of 2C+ T cells in the fetal and newborn thymus and to support their maintenance in the intestine.

Expression of the thioredoxin-thioredoxin reductase system in the inflamed joints of patients with rheumatoid arthritis

OBJECTIVE

To examine the expression of the thioredoxin (TRX)-thioredoxin reductase (TR) system in patients with rheumatoid arthritis (RA) and patients with other rheumatic diseases.

METHODS

Levels of TRX in plasma and synovial fluid (SF) were measured using enzyme-linked immunosorbent assay. Cellular distribution of TRX was determined by flow cytometry and histochemistry. Cellular expression of TR was studied by in situ messenger RNA (mRNA) hybridization. The effect of oxidative stress and tumor necrosis factor alpha (TNF alpha) on TRX expression by cultured rheumatoid fibroblast-like synoviocytes was studied.

RESULTS

Significantly increased TRX levels were found in the SF from 22 patients with RA, when compared with plasma levels in the same patients (P < 0.001) and compared with SF TRX levels in 15 patients with osteoarthritis (P < 0.001), 13 patients with gout (P < 0.05), and 9 patients with reactive arthritis (P < 0.0001). The presence of TRX could be demonstrated within the SF-derived mononuclear cells and synovial tissue (ST) of RA patients. Concordantly, expression of TR mRNA was observed in the ST of these patients. Stimulation of synovial fibroblast-like synoviocytes with either H2O2 or TNF alpha induced an increase in the production of TRX.

CONCLUSION

The data demonstrate significantly increased concentrations of TRX in the SF and ST of RA patients when compared with the levels in patients with other joint diseases. Evidence is presented that the local environment in the rheumatic joint contributes to increased TRX production. Based on its growth-promoting and cytokine-like properties, it is proposed that increased expression of TRX contributes to the disease activity in RA.

Treatment with monoclonal anti-tumor necrosis factor alpha antibody results in an accumulation of Th1 CD4+ T cells in the peripheral blood of patients with rheumatoid arthritis

OBJECTIVE

In rheumatoid arthritis (RA), treatment with tumor necrosis factor alpha (TNFalpha) binding agents has proven to be highly effective. Downregulation of the proinflammatory cytokine cascade and a reduced migration of leukocytes into the joints have been proposed as modes of action of TNFalpha blockade. We investigated whether alterations in the number of circulating pro- and antiinflammatory T cell subsets contribute to the therapeutic effect of monoclonal antibodies (mAb) against TNFalpha in RA patients.

METHODS

Phenotypic analysis of peripheral blood T cell subsets was performed on blood from RA patients before and after treatment with an anti-TNFalpha mAb.

RESULTS

An accumulation of primed CD45RA- T cells of both the CD4+ and the CD8+ T cell population was seen shortly after treatment. Most notably, within the CD4+,CD45RA- T cell subset, the number of interferon-gamma-producing T cells was significantly increased after anti-TNFalpha mAb treatment, resulting in a significant rise in the Th1:Th2 ratio. In addition, an increase in the number of CD4+ T cells expressing the homing receptor CD49d in high density was observed after treatment, which correlated positively with the increase in the Th1:Th2 ratio. Conclusion. We show that the Th1:Th2 ratio in the peripheral blood is raised by anti-TNFalpha mAb treatment.

Characterization of the hyporesponsiveness of synovial T-Cells in rheumatoid arthritis: role of chronic oxidative stress

It is commonly thought that autoreactive T-cells fulfill a central role in the chronic inflammatory response that occurs in the joints of patients with rheumatoid arthritis (RA). However, the accumulated T-cells in the joints of patients with RA are functionally suppressed compared with peripheral blood T-cells. The mechanism that underlies this synovial T-cell hyporesponsiveness and the possible role of this phenomenon in the pathogenesis of RA is the subject of this article.

CD28 co-stimulation is intact and contributes to prolonged ex vivo survival of hyporesponsive synovial fluid T cells in rheumatoid arthritis

In rheumatoid arthritis (RA), T cells in the inflamed joint are considered to play a crucial role in the pathogenesis. However, despite the fact that synovial T cells have an activated memory phenotype, they are functionally suppressed upon combined CD3 and CD28 stimulation. Here, we analyzed the contribution of both CD3 and CD28 to the hyporesponsiveness of synovial T cells in RA. In contrast to the low CD3 responsiveness of synovial fluid (SF) T cells compared to peripheral blood (PB) T cells, the CD28 co-stimulatory response was observed to be unaffected. Hyporesponsiveness of SF T cells has previously been associated with decreased levels of intracellular glutathione (GSH), an antioxidant and regulator of the intracellular redox state. Treatment of SF T cells with N-acetylcysteine, an antioxidant and replenisher of GSH, selectively improved CD3-induced responses, while leaving CD28 responsiveness unaffected. These data show that the CD3 pathway is highly sensitive to intracellular GSH alterations, whereas CD28 responsiveness is relatively refractory. Furthermore, in support for a functional role of CD28 co-stimulation, it was demonstrated that CD28 ligation acted in synergy with the IL-2 receptor gamma chain signaling cytokine IL-15 in the enhancement of the ex vivo survival of SF T cells. These data indicate that CD28 co-stimulatory capacity of SF T cells, in contrast to CD3 stimulation, remains intact despite an altered intracellular redox state. Thereby, CD28 stimulation may contribute to the persistence of T cells at the site of inflammation, which might be of relevance in the pathogenesis of RA.

Defective TCR-mediated signaling in synovial T cells in rheumatoid arthritis

In rheumatoid arthritis (RA), the functional status of T cells is incompletely understood. Synovial T cells display phenotypic evidence of former activation, but there is poor production of T cell-derived cytokines in the synovium. In addition, synovial T cell proliferation upon mitogenic and antigenic stimulation was decreased compared with that in peripheral blood T cells. Moreover, previous reports revealed that early Ca2+ rises induced by TCR/CD3 stimulation were decreased in RA T cells compared with those in healthy controls. To investigate the molecular mechanisms of RA synovial T cell hyporesponsiveness, we analyzed the TCR/CD3-mediated protein tyrosine phosphorylation in RA peripheral blood and synovial fluid (SF) T cells. SF T cells exhibited a decreased overall tyrosine phosphorylation pattern upon stimulation. Most notably, the induction of phosphorylation of p38 was virtually absent. Moreover, we found that tyrosine phosphorylation of the TCR zeta-chain, one of the most proximal events in TCR signaling, is clearly diminished in RA SF T cells. The decrease in tyrosine phosphorylation was accompanied by a decrease in detectable levels of zeta-protein within synovial T cells. These results suggest that a defective TCR signaling underlies the hyporesponsiveness of synovial T cells in RA.

Defective TCR-mediated signaling in synovial T cells in rheumatoid arthritis

In rheumatoid arthritis (RA), the functional status of T cells is incompletely understood. Synovial T cells display phenotypic evidence of former activation, but there is poor production of T cell-derived cytokines in the synovium. In addition, synovial T cell proliferation upon mitogenic and antigenic stimulation was decreased compared with that in peripheral blood T cells. Moreover, previous reports revealed that early Ca2+ rises induced by TCR/CD3 stimulation were decreased in RA T cells compared with those in healthy controls. To investigate the molecular mechanisms of RA synovial T cell hyporesponsiveness, we analyzed the TCR/CD3-mediated protein tyrosine phosphorylation in RA peripheral blood and synovial fluid (SF) T cells. SF T cells exhibited a decreased overall tyrosine phosphorylation pattern upon stimulation. Most notably, the induction of phosphorylation of p38 was virtually absent. Moreover, we found that tyrosine phosphorylation of the TCR zeta-chain, one of the most proximal events in TCR signaling, is clearly diminished in RA SF T cells. The decrease in tyrosine phosphorylation was accompanied by a decrease in detectable levels of zeta-protein within synovial T cells. These results suggest that a defective TCR signaling underlies the hyporesponsiveness of synovial T cells in RA.

Evidence for the role of an altered redox state in hyporesponsiveness of synovial T cells in rheumatoid arthritis

In rheumatoid arthritis (RA), T cells isolated from the synovial fluid (SF) show impaired responses to mitogenic stimulation compared with T cells from the peripheral blood (PB). Here it is reported that hyporesponsiveness of SF T cells correlated with a significant decrease in the levels of the intracellular redox-regulating agent glutathione (GSH). GSH was decreased in both CD4+ (p = 0.0022) and CD8+ (p = 0.0010) SF T cell subsets compared with PB CD4+ and CD8+ T cells in RA patients. Levels of thioredoxin (TRX), another key redox mediator, previously found to be secreted under conditions of oxidative stress, were found to be significantly increased in SF compared with plasma samples of RA patients (p = 0.005). Increased levels of TRX in the SF of inflamed joints was found to be associated with RA when compared with other arthritides (p = 0.007). Restoration of GSH levels in SF T cells with N-acetyl-L-cysteine (NAC), enhanced mitogenic induced proliferative responses and IL-2 production. Collectively, these data impute an important role to an altered redox state in the hyporesponsiveness of joint T cells in patients with RA.

Evidence for the role of an altered redox state in hyporesponsiveness of synovial T cells in rheumatoid arthritis

In rheumatoid arthritis (RA), T cells isolated from the synovial fluid (SF) show impaired responses to mitogenic stimulation compared with T cells from the peripheral blood (PB). Here it is reported that hyporesponsiveness of SF T cells correlated with a significant decrease in the levels of the intracellular redox-regulating agent glutathione (GSH). GSH was decreased in both CD4+ (p = 0.0022) and CD8+ (p = 0.0010) SF T cell subsets compared with PB CD4+ and CD8+ T cells in RA patients. Levels of thioredoxin (TRX), another key redox mediator, previously found to be secreted under conditions of oxidative stress, were found to be significantly increased in SF compared with plasma samples of RA patients (p = 0.005). Increased levels of TRX in the SF of inflamed joints was found to be associated with RA when compared with other arthritides (p = 0.007). Restoration of GSH levels in SF T cells with N-acetyl-L-cysteine (NAC), enhanced mitogenic induced proliferative responses and IL-2 production. Collectively, these data impute an important role to an altered redox state in the hyporesponsiveness of joint T cells in patients with RA.

Heterogeneity of the circulating human CD4+ T cell population. Further evidence that the CD4+CD45RA-CD27- T cell subset contains specialized primed T cells

CD27, a member of the TNFR family, is expressed on most but not all peripheral blood CD4+ T cells. The small fraction of CD4+ T cells with a CD27- phenotype exclusively reside within the CD45RA-CD45RO+ subset. We previously provided evidence that CD27- cells are functionally differentiated cells that have lost CD27 expression as a result of persistent antigenic stimulation. We here show that compared with CD4+CD45RA-CD27+ cells, CD4+CD45RA-CD27- lymphocytes have a high expression of the beta 1 integrins VLA-4 and -5 and of the beta 2 integrin CD11b. Molecules implicated in homing of T cells to peripheral lymphnodes like CD31 and CD62L (L-selectin) are poorly expressed on CD27- cells, whereas receptors involved in organ-specific homing, e.g., cutaneous lymphocyte Ag and HML-1 (alpha E beta 7), are present on CD27- rather than CD27+ T lymphocytes. CD27+ and CD27- cells do not differ notably in the expression of activation molecules such as CD25, CD38, and CD70 (CD27 ligand) but CD7 is markedly absent on approximately half of the CD27- cells. Analysis of mutations in the HPRT gene, as measurement for the amount of cell divisions that have occurred in particular T cell populations in vivo, showed that CD45R0+ cells have a 2 to 5 times higher mutant frequency than CD45RA+ cells, whereas CD45R0+CD27- cells do not differ in this respect from CD45R0+CD27+ cells. In line with this latter finding, cells in G2M phase can only be found in the transitional, CD45RAbrightCD45R0bright subset but not in CD45R0+, CD45RA-, or CD27- cells. Our results imply that the CD27- population contains tissue-specific, specialized "primed" T cells that evolve in vivo independently from extensive cellular division.

Joint-derived T cells in rheumatoid arthritis proliferate to antigens present in autologous synovial fluid

The histopathological features of rheumatoid joint-inflammation suggest that an antigen-driven activation of T cells plays a central role in the onset and/or perpetuation of the inflammatory process. However, the disease-associated antigens responsible for the activation of T cells in the joint are unknown. In this project we study the response of IL-2 expanded T-cell lines from the synovial fluid (SF) of rheumatoid arthritis (RA) patients against autologous SF in a proliferation assay. Sixteen out of 32 RA patients were found to have CD4+ T cells that proliferate in response to autologous SF. The presence of T cells able to respond to SF antigens in inflamed joints suggests that these T cells play an active role in the pathogenesis of RA. T cell clones reactive to autologous SF were isolated from SF-derived T-cell lines of two RA patients. All clones were of the CD4+, CD8-, alpha/beta+ phenotype. SF-reactivity of T-cell clones from the DR4/DR12-positive RA patient was restricted via the Dw4 subtype of DR4. SF reactivity of T cells of the DR12/DR15 patient was DP-restricted. Some of the T-cell clones responded specifically to autologous and not to allogeneic SF, whereas others revealed responsiveness against a limited number of allogeneic SF samples. The (restricted) specificity of T cells towards autologous SF antigens is indicative for heterogeneity of the epitopes recognized and argues against ubiquitous nonpolymorphic joint constituents as the relevant antigens recognized by the SF-autoreactive T cells.

Heterogeneity of the circulating human CD4+ T cell population. Further evidence that the CD4+CD45RA-CD27- T cell subset contains specialized primed T cells

CD27, a member of the TNFR family, is expressed on most but not all peripheral blood CD4+ T cells. The small fraction of CD4+ T cells with a CD27- phenotype exclusively reside within the CD45RA-CD45RO+ subset. We previously provided evidence that CD27- cells are functionally differentiated cells that have lost CD27 expression as a result of persistent antigenic stimulation. We here show that compared with CD4+CD45RA-CD27+ cells, CD4+CD45RA-CD27- lymphocytes have a high expression of the beta 1 integrins VLA-4 and -5 and of the beta 2 integrin CD11b. Molecules implicated in homing of T cells to peripheral lymphnodes like CD31 and CD62L (L-selectin) are poorly expressed on CD27- cells, whereas receptors involved in organ-specific homing, e.g., cutaneous lymphocyte Ag and HML-1 (alpha E beta 7), are present on CD27- rather than CD27+ T lymphocytes. CD27+ and CD27- cells do not differ notably in the expression of activation molecules such as CD25, CD38, and CD70 (CD27 ligand) but CD7 is markedly absent on approximately half of the CD27- cells. Analysis of mutations in the HPRT gene, as measurement for the amount of cell divisions that have occurred in particular T cell populations in vivo, showed that CD45R0+ cells have a 2 to 5 times higher mutant frequency than CD45RA+ cells, whereas CD45R0+CD27- cells do not differ in this respect from CD45R0+CD27+ cells. In line with this latter finding, cells in G2M phase can only be found in the transitional, CD45RAbrightCD45R0bright subset but not in CD45R0+, CD45RA-, or CD27- cells. Our results imply that the CD27- population contains tissue-specific, specialized "primed" T cells that evolve in vivo independently from extensive cellular division.

Simultaneous regulation of CD2 adhesion and signaling functions by a novel CD2 monoclonal antibody

Accessory molecules on T cells can support adhesion and transduce agonistic signals that facilitate Ag receptor-induced T cell activation. The T cell differentiation Ag CD2 may exert both functions, as has been amply demonstrated in studies with CD2 mAbs. In addition, experiments in which either purified ligand (CD58) or transfected CD2 and CD58 molecules were used have confirmed this notion. However, controversy exists as to whether CD2 alters its affinity for CD58 in the course of T cell stimulation, and whether this putative affinity change affects CD2-mediated activation signals. We now describe a CD2 mAb (HIK27) that recognizes an epitope constitutively expressed on resting T cells and induces increased adhesiveness of CD2 toward CD58. Addition of HIK27 to a stimulatory but nonmitogenic pair of CD2 mAbs induces a strong proliferative response. Finally, HIK27 was found to be co-mitogenic with CD58 expressed on sheep erythrocytes, B cell lines, and CD58-transfected L cells. The simultaneous modulation of CD2 adhesion and signaling on HIK27 binding suggests that both functions of the molecule may be enhanced in the course of T cell stimulation.

Simultaneous regulation of CD2 adhesion and signaling functions by a novel CD2 monoclonal antibody

Accessory molecules on T cells can support adhesion and transduce agonistic signals that facilitate Ag receptor-induced T cell activation. The T cell differentiation Ag CD2 may exert both functions, as has been amply demonstrated in studies with CD2 mAbs. In addition, experiments in which either purified ligand (CD58) or transfected CD2 and CD58 molecules were used have confirmed this notion. However, controversy exists as to whether CD2 alters its affinity for CD58 in the course of T cell stimulation, and whether this putative affinity change affects CD2-mediated activation signals. We now describe a CD2 mAb (HIK27) that recognizes an epitope constitutively expressed on resting T cells and induces increased adhesiveness of CD2 toward CD58. Addition of HIK27 to a stimulatory but nonmitogenic pair of CD2 mAbs induces a strong proliferative response. Finally, HIK27 was found to be co-mitogenic with CD58 expressed on sheep erythrocytes, B cell lines, and CD58-transfected L cells. The simultaneous modulation of CD2 adhesion and signaling on HIK27 binding suggests that both functions of the molecule may be enhanced in the course of T cell stimulation.

Epstein-Barr virus DNA in Reed-Sternberg cells of Hodgkin's disease is frequently associated with CR2 (EBV receptor) expression

We studied 44 cases of Hodgkin's disease for the presence of Epstein-Barr virus (EBV) DNA, its localization and the expression of the EBV receptor on the tumour cells. EBV DNA was found in 52% (16/31) of the Hodgkin's lymphomas using the polymerase chain reaction. With a very sensitive non-radioactive DNA in situ hybridization technique in combination with immunohistochemistry for CD 30 or CD 15 antigens, EBV DNA was localized to Reed-Sternberg cells and its mononuclear variants. The relationship between the presence of EBV DNA and the expression of the EBV-receptor CR2 (CD 21) on Reed-Sternberg cells was studied using the same techniques and two different monoclonal anti-CD 21 antibodies. CR2 could be detected on a substantial number of the Reed-Sternberg cells in EBV DNA positive Hodgkin's lymphomas (9/12; 75%), whereas in EBV negative cases positivity with anti-CD 21 was rare (1/13; 8%). The results indicate that CR2 expression on Reed-Sternberg cells and the presence of EBV DNA sequences are frequently associated in Hodgkin's lymphomas.