A possible role of apoptosis for regulating autoreactive responses in systemic lupus erythematosus

CD4 T lymphocyte subsets display heterogeneous susceptibility to apoptosis induced by serum from patients with systemic lupus erythematosus

BACKGROUND

Serum from systemic lupus erythematosus (SLE) patients has been shown to induce T-lymphocyte (TL) apoptosis. Given that different cells of the immune system display different sensitivity to apoptosis, we set to evaluate the in vitro effect of SLE serum on regulatory T-cells (Treg), Th17, Th1 and Th2 from SLE patients and healthy controls.

METHODS

Peripheral blood mononuclear cells from SLE patients or normal controls were exposed to a pool of sera from SLE patients or normal controls. Annexin V was used to label cells in apoptosis or necrosis. Annexin V-labeled Treg, Th17, Th1 and Th2 cells were determined using flow cytometry.

RESULTS

Total CD3 + and CD4 + cells from SLE patients showed higher frequency of spontaneous apoptosis/necrosis, whereas Th1 cells from SLE patients presented reduced spontaneous apoptosis/necrosis rate as compared with cells from controls. Incubation with SLE serum induced increased frequency of apoptotic/necrotic CD3 + , CD4 + and Th2 cells from normal controls or from SLE patients as compared with cultures incubated with normal human serum (NHS) or without human serum at all. Incubation with SLE serum did not increase the apoptosis/necrosis rate in Th1 or Th17 cells. Treg cells from SLE patients were more prone to apoptosis/necrosis induced by SLE serum than Treg cells from normal individuals. Th1, Th2, and Th17 cells presented increased apoptosis rates in cultures without human serum.

CONCLUSION

Our findings indicate that the serum of patients with active SLE stimulates apoptosis of CD4 + T cells in general and exhibit differentiated effects on CD4 + T-cell subsets.

An Lck-cre transgene accelerates autoantibody production and lupus development in (NZB × NZW)F1 mice

Lupus is an autoimmune disease characterized by the development of antinuclear autoantibodies and immune complex-mediated tissue damage. T cells in lupus patients appear to undergo apoptosis at an increased rate, and this enhanced T cell apoptosis has been postulated to contribute to lupus pathogenesis by increasing autoantigen load. However, there is no direct evidence to support this hypothesis. In this study, we show that an Lck-cre transgene, which increases T cell apoptosis as a result of T cell-specific expression of cre recombinase, accelerates the development of autoantibodies and nephritis in lupus-prone (NZB × NZW)F1 mice. Although the enhanced T cell apoptosis in Lck-cre transgenic mice resulted in an overall decrease in the relative abundance of splenic CD4(+) and CD8(+) T cells, the proportion of activated CD4(+) T cells was increased and no significant change was observed in the relative abundance of suppressive T cells. We postulate that the Lck-cre transgene promoted lupus by enhancing T cell apoptosis, which, in conjunction with the impaired clearance of apoptotic cells in lupus-prone mice, increased the nuclear antigen load and accelerated the development of anti-nuclear autoantibodies. Furthermore, our results also underscore the importance of including cre-only controls in studies using the cre-lox system.

Increased serum IL-10 in lupus patients promotes apoptosis of T cell subsets via the caspase 8 pathway initiated by Fas signaling

We sought to investigate the expression of Fas and FasL on T cell surface and caspase 8 involvement in T cell apoptosis promoted by serum IL-10 in systemic lupus erythematosus (SLE) patients. Cells and sera were obtained from 35 SLE patients. Apoptosis of T cells in patients with SLE was increased and associated with the SLE disease activity index (SLEDAI). Elevated expression of Fas and FasL on T cell surface contributed to increased apoptosis of T cells. Increased IL-10 in the sera of SLE patients was capable of inducing Fas and FasL expression on CD4⁺T cell surface, promoting apoptosis of this cell subset. Decreased IL-10 serum levels and low expression of Fas were found in 5 patients of the first follow-up group after 2-month treatment. In another group with one-year treatment, the SLEDAI declined to inactive scores. Serum IL-10 was decreased significantly, and expression of Fas and FasL on T cells was also reduced. Declined apoptosis was predominant only in CD4⁺T cell subset. When sera with high level of IL-10 were used to culture PBMCs from healthy controls, activated caspase 8 was elevated in CD3⁺T, CD4⁺T and CD8⁺T cells. The study showed that serum IL-10 induced apoptosis of T cell subsets via the caspase 8 pathway initiated by Fas signaling. Increased apoptosis of T cells contributes to autoantigen burden, which is pathogenic in the development of SLE.

The pathway of estradiol-induced apoptosis in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a disease with unknown etiology. The pathologic role of sex hormones and apoptosis in SLE has often been discussed. We studied the effects of estradiol in the pathway of induced apoptosis in Iranian SLE patients. T lymphocytes from 35 SLE patients and 20 age-matched controls were isolated and cultured in the presence of 10(-8) M 17-β estradiol. The expression levels of Fas, Fas ligand (FasL), Bcl-2, caspase-8, and caspase-9 mRNAs were determined semiquantitatively in comparison to the expression level of beta actin RNA. Estradiol exposure did not have any significant effects on the expression levels of Fas, Bcl-2, and caspase-9 in SLE patients and controls. However, the expression levels of FasL and caspase-8 were significantly increased in SLE patients, but not in controls. This suggests the probable involvement of extrinsic apoptosis pathway in estradiol-induced apoptosis in SLE.

Association between T lymphocyte sub-sets apoptosis and peripheral blood mononuclear cells oxidative stress in systemic lupus erythematosus

Increased oxidative stress and lymphocyte apoptosis are a hallmark of the autoimmune disease systemic lupus erythematosus (SLE). However, the association between oxidative stress and T lymphocytes apoptosis has still to be elucidated in SLE. In order to appraise the interaction between oxidative stress and T lymphocyte apoptosis with the severity of disease, oxidative stress profile and T lymphocytes apoptosis were studied. Increased levels of ROS, MDA and CD4(+) lymphocyte apoptosis were positively associated with disease activity while decreased levels of GSH and percentage expression of CD4(+) lymphocyte were negatively associated with disease activity. The decrease in intracellular levels of GSH was negatively associated with T lymphocyte, CD4(+) lymphocyte, CD8(+) lymphocyte apoptosis and intracellular caspase-3 expression. The present study suggests that increased T lymphocyte sub-sets apoptosis may be mediated by decreased intracellular glutathione concentration and severity of disease might be enhanced together by over-production of ROS in SLE.

Increased T-lymphocyte apoptosis in lupus correlates with disease activity and may be responsible for reduced T-cell frequency: a cross-sectional and longitudinal study

Apoptosis of lymphocytes is increased in patients with lupus. This may be pathogenic leading to increased load of autoantigens or may be a bystander effect of immune activation. A major unresolved issue is whether apoptosis is related to disease activity. Also its association with lymphocyte frequencies, anti-nucleosomal antibodies and serum IL 10 levels needs to be explored further. The aims of this study are to measure T- and B-lymphocyte apoptosis in patients with lupus and look at the effect of disease activity in a cross-sectional and longitudinal design and to determine frequency of T and B cells, level of anti-nucleosomal antibodies and serum IL 10 and assess their relationship with apoptosis. This study included 41 patients with SLE and 20 controls. A cutoff value of 4 in systemic lupus erythematosus disease activity index (SLEDAI) was used to separate active from inactive SLE. The frequency and degree of apoptosis of T and B lymphocyte were enumerated by flow cytometry using peripheral blood mononuclear cells (PBMCs) stained with CD3/CD19 and annexin V/PI. The data for T/B cell frequency are represented as % of these cells in the PBMC population, whereas percentage of apoptotic cells is out of total T or B cells. Serum anti-nucleosomal antibodies and IL 10 were assayed using ELISA. A repeat assessment of these parameters was carried out in 11 active patients when they became inactive. We found higher T-lymphocyte apoptosis in patients with SLE versus controls (14.8 +/- 9.2, 7.2 +/- 3.0; P < 0.05) and a lower frequency of T cells (72.7 +/- 12.6, 79.9 +/- 5.8; P < 0.05). T-lymphocyte apoptosis was higher in patients with active disease compared with inactive (18.5 +/- 11.3, 11.6 +/- 5.4; P = 0.05). Further, T-lymphocyte apoptosis directly correlated with SLEDAI (r = 0.37, P < 0.05) and inversely with T-cell frequency (r = -0.29, P < 0.05). Anti-nucleosomal antibodies correlated with SLEDAI but not apoptosis. On longitudinal follow-up, a decline in T-cell apoptosis was seen in patients with SLE, however this was not statistically significant. We confirmed a higher degree of apoptosis in T-lymphocytes in patients with SLE and found a direct correlation of T-cell apoptosis with disease activity. Patients had reduced T-cell frequency, which inversely correlated with T-cell apoptosis and may suggest a cause-effect relationship.

Elevated levels of soluble Fas (APO-1, CD95), soluble Fas ligand, and matrix metalloproteinase-3 in sera from patients with active untreated adult onset Still’s disease

To investigate serum levels of soluble Fas (sFas), soluble Fas ligand (sFas-L), and matrix metalloproteinase-3 (MMP-3) in patients with active untreated adult onset Still's disease (AOSD). Serum levels of sFas, sFas-L, and MMP-3 were determined by enzyme-linked immunosorbent assays in 20 patients with active untreated AOSD, 20 patients with active rheumatoid arthritis (RA), and 20 healthy controls. Linear regression was used to evaluate the correlation between clinical activity scores and serum levels of sFas, sFas-L, and MMP-3 in AOSD patients. Significantly higher levels of sFas, sFas-L, and MMP-3 in sera were found in active untreated AOSD patients compared to healthy controls. Serum levels of sFas, sFas-L, and MMP-3 correlated well with clinical activity scores of AOSD patients (r=0.467, 0.694, and 0.798, respectively). There was a significant correlation between CRP values and serum levels of sFas-L as well as MMP-3 (r=0.583 and r=0.582, respectively, both p<0.01), and a positive correlation between serum sFas-L levels and serum MMP-3 levels (r=0.726, p<0.001) in AOSD patients. Significantly higher levels of serum sFas-L were found in AOSD patients than in RA patients. Serum levels of sFas, sFas-L, and MMP-3 fluctuated and were found to be parallel to disease activity of AOSD. sFas, sFas-L, and MMP-3, which were significantly elevated in sera of active untreated AOSD patients and paralleled disease activity, may be involved in the pathogenesis of this disease. Further studies are needed to determine the pathophysiologic role of sFas, sFas-L, and MMP-3 in AOSD.

Mycophenolic acid inhibits SLE-associated cytokine expression and promotes apoptosis of peripheral blood mononuclear cells from patients with systemic lupus erythematosus

AIM

To investigate the effect of the novel immunosuppressant mycophenolic acid (MPA) on cytokine production and apoptosis of the peripheral blood mononuclear cells (PBMC) of patients with systemic lupus erythematosus (SLE).

METHODS

The levels of IL-10, IL-12, IFN-gamma, sFas and sFasL in the supernatants of cultured PBMC from 41 SLE patients was determined by the ABC-ELISA method. The percentage of IFN-gamma(+)IL-10(-), IFN-gamma(-)IL-10(+), and IFN-gamma(+)IL-10(+) subsets in CD4+ cells were detected by three-color flow cytometry. The percentage of apoptotic Th cells was detected by AV-FITC/PI flow cytometry. Samples from 22 sex- and age-comparable healthy people were used as normal controls.

RESULTS

The levels of IL-10, IL-12, and IFN-gamma were all significantly elevated in the supernatants of cultured PBMC from SLE samples, compared with normal controls. The enhanced productions of IL-10, IL-12, and IFN-gamma by PBMC from SLE both spontaneously and stimulated by phytohaemagglutinin (PHA) were significantly reduced by MPA. The percentages of CD4(+)IFN-gamma(-)IL-10(+) and CD4(+)IFN-gamma(+)IL-10(+) cell subsets in cultured PBMC from SLE were significantly increased, but decreased when MPA was added into the culture. After being cultured in vitro for 48 h, the PBMC of SLE patients showed a higher secretion of sFasL as well as a higher percentage of apoptosis. MPA significantly increased the apoptotic percentage of SLE PBMC, but reduced the secretion of sFasL and sFas.

CONCLUSION

MPA reduces the abnormal production of SLE-associated cytokines, such as IL-10, IL-12, and IFN-gamma; inhibits the increase of CD4(+)IFN-gamma(+)IL-10, CD4(+)IFN-gamma(-)IL-10(+) and CD4(+)IFN-gamma(+)IL-10(+) subset; and promotes the apoptosis of PBMC in SLE patients, which may be associated with the therapeutic mechanism of MPA for SLE.

Peripheral blood lymphocyte apoptosis and circulating dendritic cells in patients with systemic lupus erythematosus: correlation with immunological status and disease-related symptoms

We investigated in vivo the relationship between the degree of peripheral blood lymphocyte apoptosis and circulating dendritic cells (DC) as well as the immunological status in 45 patients with systemic lupus erythematous (SLE). Apoptosis was detected by phosphatidylserine externalization and assays to detect caspase activation. The total DC count (tDC) and their myeloid, mDC1 (BDCA1+) and mDC2 (BDCA3+), and plasmacytoid, pDC (BDCA3+), subtypes were assessed. Moreover, several immunological parameters, such as complement proteins, interferons (IFN), tumor necrosis factor (TNF)-alpha, interleukin (IL)-4, and IL-6 levels were assessed. There were no significant differences in both the intensity of apoptosis and DC counts between active and inactive SLE as well as between untreated patients and those treated with steroids. The incidence of lymphocyte apoptosis correlated positively with T-cell count, both T-helper (p=0.004) and cytotoxic T cells (p=0.001), but not with B or natural killer (NK) cells. The intensity of apoptosis enhanced along with the increase in complement C3 (p=0.016) and decrease in IFN-gamma (p=0.040) levels. The apoptotic cell count correlated with tDC (p=0.031), mDC1 (p=0.007), and pDC (p=0.039) counts. Both tDC and mDC1 counts correlated positively with antinuclear antibody (ANA) titers (p=0.017 and 0.032, respectively). Moreover, tDC correlated with C4 (p=0.039) and pDC with both C3 (p=0.032) and C4 (p=0.007) levels. The DC counts correlated inversely with IFN-gamma (tDC, p=0.038; mDC1, p=0.009), IL-6 (mDC2, p=0.031), or serum IgG levels (tDC, p=0.006; mDC1, p<0.001; mDC2, p=0.001). We found a positive correlation between lymphocyte apoptosis and peripheral blood DC count as well as the level of complement proteins in patients with SLE. The enhanced lymphocyte apoptosis was accompanied by the decrease in concentration of some cytokines, such as IFN-gamma or IL-6, as well as serum IgG level. This finding may reflect pathogenetic events during development of the disease, which include a persistent signal derived from circulating apoptotic lymphocytes, mobilizing the complement system, and attracting peripheral blood DC.

The abnormal apoptosis of T cell subsets and possible involvement of IL-10 in systemic lupus erythematosus

To study the apoptosis of lymphocyte subpopulations in systemic lupus erythematosus (SLE) patients and the possible role of IL-10 in this apoptosis involved in the pathogenesis of SLE, three color fluorescence and flow cytometry were used to investigate the early apoptosis of lymphocyte subsets from freshly separated or cultured peripheral blood mononuclear cells (PBMCs). ELISA was employed to detect the levels of IL-10 in serum and the levels of sFas and sFasL in cultured PBMC supernatants, and the results of sFas and sFasL were confirmed by real-time PCR of Fas and FasL mRNA. The results showed that in cells from SLE patients, the apoptosis of CD3+, CD4+, and CD8+ T cells was distinctly increased, and the percentage of CD4+ cells and the CD4/CD8 ratio was significantly decreased, as compared with normal controls. The apoptosis of T lymphocytes cultured with SLE serum was markedly higher than that of cells cultured with control's serum. Blockade of interleukin-10 (IL-10) activation by an anti-IL-10 antibody reduced the SLE serum induced apoptosis of CD4+ and CD8+ T cells. The levels of sFas and sFasL in the culture supernatant and Fas and FasL mRNA expressions in cultured cells were significantly higher in the SLE serum-cultured groups, but decreased evidently in the presence of the anti-IL-10 antibody. Above findings suggested that SLE cells showed abnormally high apoptosis of T lymphocytes, especially of the CD4+ subpopulation, resulting in a decreased CD4/CD8 ratio. The high percentage of apoptotic T cells in SLE patients may be related to the high levels of IL-10 in SLE serum, as IL-10 may induce the abnormally activated T cells to trigger apoptosis via the Fas-FasL pathway.

Apoptosis: the link between autoantibodies and leuko-/lymphocytopenia in patients with lupus erythematosus

OBJECTIVE

To analyse the relation between serum autoantibodies and leuko-/lymphocytopenia in patients with lupus erythematosus (LE).

METHODS

Laboratory routine analyses (white blood cell counts, autoantibody detection), and flow cytometry (annexin V, CD3, CD4, CD8, CD95, F(ab)2 anti-human IgG) have been performed in LE-patients versus healthy controls. In vitro, the influence of pooled serum containing anti-dsDNA antibodies has been analysed on the CD95 expression.

RESULTS

Leukocytes, lymphocytes, CD3+, CD3+ CD4+, and CD3+ CD8+ cells from LE-patients were significantly reduced compared with controls. Patients with autoantibodies had significantly lower absolute cell counts than those without. Apoptosis was increased in LE versus controls (p < 0.04). The percentage of CD95+ T-cells was increased, and the absolute number of CD95+ cells was reduced in LE. In vitro up-regulation of CD95 could be detected on T-cells of healthy donors. Induction of CD95 seems to be donor-dependent.

CONCLUSION

The data suggest that autoantibodies may be associated with blood cytopenias. CD95 seems to play a central role in this signalling cascade. The underlying mechanism is unclear, but seems to be autoantibody-related apoptosis induction.

Genetic dissection of systemic autoimmune disease in Nrf2-deficient mice

Systemic lupus erythematosus (SLE) is an autoimmune disorder with immune-complex deposition that affects multiple organs. Previous studies have suggested the involvement of oxidative stress and apoptosis in SLE, but no clear link to etiology has been established. Here we show that mice deficient in a transcription factor responsible for controlling the expression of numerous detoxification and antioxidant genes develop an autoimmune disease with multiple organ pathologies that closely resembles human SLE. Aged female mice with a knockout of nuclear factor, erythroid-derived 2, like 2 (nrf2) are prone to develop antibodies against double-stranded DNA and the Smith antigen as well as IgG, IgM, and C3 deposition in kidney, liver, heart, and brain. Prior to the development of autoimmune antibodies and organ pathology, oxidative damage occurs in the liver and kidney as indicated by the increased levels of the DNA oxidation marker 8-hydroxydeoxyguanosine and the later increase in the lipid peroxidation product malondialdehyde. Gene expression profiles demonstrate an early decrease in numerous antioxidant and detoxification genes in the livers and altered levels of cytokines and T and B cell-specific genes in the spleens of nrf2 knockout mice. These data strongly suggest that a deficiency in detoxification and increased oxidative stress can result in the development of a systemic autoimmune disease.

Programmed cell death in rheumatoid arthritis peripheral blood T-cell subpopulations determined by laser scanning cytometry

Because peripheral blood mononuclear cells play an important role in the perpetuation of the autoimmune process in rheumatoid arthritis (RA) and because the maintenance of these cells might be caused by the dysregulation of apoptosis, we investigated the apoptosis susceptibility of peripheral blood mononuclear cells from patients with RA. Freshly separated peripheral blood lymphocytes were stained for apoptosis markers (CD95, Bax, Bcl-2, TNF receptor) and for an activation marker (CD45-RO), and the apoptosis frequency of cells bearing these markers were assessed by the terminal-deoxynucleotidyl transferase-mediated dUTP digoxigenin nick end labeling method and nuclear condensation analysis with laser scanning cytometry. Also, the ability of CD4(+) and CD8(+) T-cell populations to undergo apoptosis was investigated with 24-hour culture in medium alone or with different apoptosis inducers (anti-CD3, anti-CD95, anti-TNF receptor). Laser scanning cytometry analysis was used to enumerate the phenotype and apoptosis ratios of both freshly isolated and cultured lymphocytes. Quantitative ELISA was performed to detect plasma levels of TNF-alpha and soluble Fas ligand. Furthermore, we studied the relationship between marked apoptotic defects in patients with RA and the severity of clinical disease. CD4(+) T-cell counts in patients with RA were elevated compared with controls. A decreased rate of anti-CD95-mediated apoptosis was found within the CD4(+) and CD8(+) lymphocytic subpopulations. In patients with RA, decreased Bax expression and decreased apoptosis rate within the Bax-positive cells were found, whereas Bcl-2 expression was elevated. The CD45-RO expression was higher, whereas the apoptosis within CD45-RO(+) cells were decreased in RA. Evaluation of plasma soluble Fas ligand revealed significantly decreased levels in patients compared with controls. The reduced susceptibility to CD95-mediated apoptosis may contribute to the expansion of an activated CD4(+) lymphocyte subpopulation and thus to the maintenance of peripheral autoreactive T-cell clones in RA. We also revealed a relationship between in vitro demonstrated lymphocyte apoptosis defects and clinical disease activity.

Oxygen free radicals and systemic autoimmunity

Reactive oxygen species generated during various metabolic and biochemical reactions have multifarious effects that include oxidative damage to DNA leading to various human degenerative and autoimmune diseases. The highly reactive hydroxy radical (*OH) can interact with chromatin and result in a wide range of sugar and base-derived products, DNA-protein cross-links and strand breaks. Studies from our laboratory have demonstrated that after modification the DNA becomes highly immunogenic and the induced antibodies exhibit variable antigen-binding characteristics. Systemic lupus erythematosus, a prototype autoimmune disease, is characterized by the presence of autoantibodies to multiple nuclear antigens. The detection of 8-hydroxyguanosine in the immune complex derived DNA of systemic lupus erythematosus patients reinforces the evidence that reactive oxygen species may be involved in its pathogenesis. Increased apoptosis and decreased clearance of apoptotic cells as observed in systemic lupus erythematosus (SLE) might well be a contributory factor in systemic autoimmunity. Clinically, titres of autoantibodies are closely related to the degree of renal inflammation. Anti-DNA antibodies may combine with circulating antigen and contribute to the deposition of immune complexes in renal glomeruli.

Fas expression on peripheral blood lymphocytes in systemic lupus erythematosus (SLE): relation to lymphocyte activation and disease activity

Levels of apoptotic lymphocytes have been found to be increased in SLE and persistence of apoptotic cells has been associated with autoantibody production. Increased lymphocyte Fas (CD95) expression due to lymphocyte activation may account for increased susceptibility to Fas-mediated apoptosis in SLE. Flowcytometry was performed to evaluate membrane expression of Fas in combination with the activation markers CD25, HLA-DR and CD38 on, respectively, CD4+, CD8+ and CD19+ lymphocytes of SLE patients with inactive (n = 20) and with active disease (n = 13). SLEDAI-scores were calculated. Healthy volunteers (n = 14) served as controls. Percentages of CD4+ T-cells expressing CD25 and CD19+ B-cells expressing CD38 were increased in patients with active disease compared to controls (P = 0.03, P = 0.04, respectively). In contrast to CD4+ and CD8+ cells, percentages of CD19+ cells expressing Fas were increased in SLE patients with active disease (P = 0.0002 vs controls). In these patients percentages of cells double positive for both CD38 and Fas were increased compared to patients with inactive disease (P = 0.006) and controls (P = 0.0007). Percentages of CD19+ cells expressing Fas correlated with SLEDAI-scores. In SLE patients, percentages of Fas-expressing B-lymphocytes are increased, are related to the state of lymphocyte activation, and correlate to disease activity. Increased Fas expression results in a higher susceptibility for Fas-mediated apoptosis, which might contribute to the increased levels of apoptotic lymphocytes in SLE patients.