Defective T cell receptor/CD3 complex signaling in human type I diabetes

Cluster of differentiation molecules in the metabolic syndrome

Metabolic syndrome (MetS) represents a significant public health concern due to its association with an increased risk of cardiovascular disease, type 2 diabetes, and other serious health conditions. Despite extensive research, the underlying molecular mechanisms contributing to MetS pathogenesis remain elusive. This review aims to provide a comprehensive overview of the molecular mechanisms linking MetS and cluster of differentiation (CD) markers, which play critical roles in immune regulation and cellular signaling. Through an extensive literature review with a systematic approach, we examine the involvement of various CD markers in MetS development and progression, including their roles in adipose tissue inflammation, insulin resistance, dyslipidemia, and hypertension. Additionally, we discuss potential therapeutic strategies targeting CD markers for the management of MetS. By synthesizing current evidence, this review contributes to a deeper understanding of the complex interplay between immune dysregulation and metabolic dysfunction in MetS, paving the way for the development of novel therapeutic interventions.

Epigenetic drug ameliorated type 1 diabetes via decreased generation of Th1 and Th17 subsets and restoration of self-tolerance in CD4+ T cells

Female NOD mice develop autoimmune diabetes spontaneously without extrinsic manipulation. Previously, we have shown that weekly administration of the prediabetic female NOD mice with the histone modifier Trichostatin A (TSA) prevented diabetes onset. Herein we show that T lymphocytes from diabetic mice transferred diabetes into immunodeficient NOD.scid recipients while those isolated from drug-treated mice displayed reduced disease-causing ability. Drug treatment also repressed T cell receptor-mediated IFN-γ transcription. Splenic CD4⁺ T-cells purified from prediabetic mice could be polarized into IFN-γ -producing Th1 and IL-17A-expressing Th17 subsets ex vivo. Adoptive transfer of these cells into immunocompromised NOD.scid mice caused diabetes comparably. Polarized Th1 cells were devoid of IL-17A-producing cells and did not transdifferentiate into Th17 cells in the spleen of immunodeficient recipients. However, polarized Th17 cell preparation had a few contaminant Th1 cells. Adoptive transfer of polarized Th17 cells into NOD.scid recipients led to IFN-γ transcription in recipient splenocytes. Notably, TSA treatment of prediabetic mice abolished the ability of CD4⁺ T-cells to differentiate into diabetogenic Th1 and Th17 cells ex vivo. This was accompanied by the absence of Ifng and Il17a transcription in the spleen of NOD.scid recipients receiving cells, respectively cultured under Th1 and Th17 polarizing conditions. Significantly, the histone modifier restored the ability of CD4⁺ but not CD8⁺ T-cells to undergo CD3-mediated apoptosis ex vivo in a caspase-dependent manner. These results indicate that the histone modifier bestowed protection against type 1 diabetes via negative regulation of signature lymphokines and restitution of self-tolerance in CD4⁺ T cells.

Defects in the acquisition of tumor-killing capability of CD8+ cytotoxic T cells in streptozotocin-induced diabetic mice

Emerging evidences have shown that diabetes mellitus not only raises risk but also heightens mortality rate of cancer. It is not clear, however, whether antitumor CD8⁺ cytotoxic T lymphocyte (CTL) response is down-modulated in diabetic hosts. We investigated the impact of hyperglycemia on CTLs' acquisition of tumor-killing capability by utilizing streptozotocin-induced diabetic (STZ-diabetic) mice. Murine diabetes was induced by intraperitoneal injection of STZ (200 mg/kg) in C57BL/6 mice, 2C-T cell receptor (TCR) transgenic and P14-TCR transgenic mice. The study found that, despite harboring intact proliferative capacity measured with CFSE labeling and MTT assay, STZ-diabetic CD8⁺ CTLs displayed impaired effector functions. After stimulation, STZ-diabetic CD8⁺ CTLs produced less perforin and TNFα assessed by intracellular staining, as well as expressed less CD103 protein. Furthermore, adoptive transfer of STZ-diabetic P14 CD8⁺ effector cells showed an insufficient recruitment to the B16.gp33 melanoma and inadequate production of perforin, granzyme B and TNFα determined by immunohistochemistry in the tumor milieu. As a result, STZ-diabetic CD8⁺ effector cells were neither able to eliminate tumor nor to improve survival of tumor-bearing mice. Taken together, our data suggest that CD8⁺ CTLs are crippled to infiltrate into tumors and thus fail to acquire tumor-killing capability in STZ-diabetic hosts.

Modulatory effect of insulin on T cell receptor mediated calcium signaling is blunted in long lasting type 1 diabetes mellitus

Insulin significantly influences Ca(2+) signals evoked by various stimulants. In type 1 recent onset diabetes mellitus the proliferative response of T cells is significantly decreased. The number of clinical trials exploring the role of anti-CD3 monoclonal antibodies (mAb) as a therapeutic agent in recent onset diabetes mellitus type 1 is increasing last years. Therefore, a better understanding of the interplay between T cell receptor (TCR) dependent Ca(2+) increase, and insulin is of vital clinical significance. The aim of the study was to assess the effect of insulin on TCR evoked Ca(2+) responses in T lymphocytes obtained from healthy volunteers and patients suffering from long lasting diabetes mellitus type 1. Analysis was performed with use of the flow cytometer. We demonstrated that T cells ability to mobilize Ca(2+) was significantly reduced in long lasting diabetes mellitus type 1. Ca(2+) decrease achieved by the long term incubation with anti-CD3 mAb in T cells from healthy volunteers was restored by insulin. Strong interrelationship between baseline Ca(2+) level and plateau phase response to TCR stimulation was observed in the cytoplasm of cells pre-incubated with insulin from both healthy subjects and diabetic patients (r = 0.95, p < 0.0001 and r = 0.94, p < 0.0001, respectively). We postulate the existence of the interplay between TCR mediated activation and insulin. The TCR-insulin interplay is blunted in long lasting diabetes mellitus type 1. These observations may have an important implication for future therapeutic options in diabetes.

Immunomodulation at epithelial sites by obesity and metabolic disease

Obesity and related type 2 diabetes are increasing at epidemic proportions globally. It is now recognized that inflammatory responses mediated within the adipose tissue in obesity are central to the development of disease. Once initiated, chronic inflammation associated with obesity leads to the modulation of immune cell function. This review will focus specifically on the impact of obesity on γδ T cells, a T-cell subset that is found in high concentrations in epithelial tissues such as the skin, intestine, and lung. Epithelial γδ T cell function is of particular concern in obesity as they are the guardians of the epithelial barrier and mediate repair. A breakdown in their function, and subsequently the deterioration of the epithelium can result in dire consequences for the host. Obese patients are more prone to non-healing injuries, infection, and disease. The resulting inflammation from these pathologies further perpetuates the disease condition already present in obese hosts. Here we will provide insight into the immunomodulation of γδ T cells that occurs in the epithelial barrier during obesity and discuss current therapeutic options.

Experimental diabetes attenuates calcium mobilization and proliferative response in splenic lymphocytes from mice

The present study was conducted to investigate the effects of the diabetic condition on cytosolic free Ca(2+) concentration, [Ca(2+)](i), and the proliferation of splenic lymphocytes from mice. Diabetes was induced in mice by intraperitoneal injection of alloxan. [Ca(2+)](i) and the proliferation ex vivo of splenic lymphocytes isolated from mice were examined using fura-2 and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide, respectively. Diabetes caused a significant increase in resting [Ca(2+)](i) and significantly reduced the ability of concanavalin A (Con A; a T-lymphocyte-selective mitogen) to increase [Ca(2+)](i), but not that of lipopolysaccharide (LPS; a B-lymphocyte-selective mitogen). In addition, diabetes significantly reduced Con A-stimulated but not LPS-stimulated lymphocyte proliferation. Verapamil (an L-type Ca(2+) channel blocker) inhibited Con A-induced increases in [Ca(2+)](i) and proliferation in lymphocytes from control and diabetic mice to a similar extent, respectively. These results suggest that diabetes attenuates Con A-stimulated T-lymphocyte proliferation by decreasing [Ca(2+)](i) via reduction of Ca(2+) entry through L-type Ca(2+) channels.

Ex vivo TCR-induced leukocyte gene expression of inflammatory mediators is increased in type 1 diabetic patients but not in overweight children

BACKGROUND

Abnormal systemic concentrations of proinflammatory cytokines/chemokines have been implicated in the development of long-term cardiovascular complications in type 1 diabetes (T1DM) and obesity. Whether leukocyte white blood cell (WBC) gene expression of these proinflammatory mediators contributes to their increased systemic levels, however, remains unclear, especially in the pediatric patient populations. This study examines mRNA changes of 9 cytokines and chemokines in WBCs following ex vivo immunostimulation from 9 T1DM (13.4 +/- 0.5 year, 4F/5 M), 23 overweight (OW, 12.3 +/- 0.5 year, 10F/13M, BMI% 97.1 +/- 0.5 and > 90.0), and 21 healthy (CL, 13.8 +/- 0.7 year, 9F/12 M, BMI% 59.6 +/- 4.6 and < 85.0) children.

METHODS

All subjects had been maintained in euglycemic conditions for at least 90 min before blood draws. Whole blood was then sampled and incubated with anti-T-cell receptor (TCR) antibody or heat-aggregated IgG (HAG) to stimulate T-cell and Fc receptors (FcR), respectively. After lysis of leukocytes, mRNA levels of six tumor necrosis factor superfamily cytokines (TNFSF2, 5, 6, 7, 9, 14) and three chemokines (CCL8, 20, and CXCL10) were measured using RT-PCR.

RESULTS

Following TCR stimulation, T1DM displayed significantly greater mRNA responses than CL for TNFSF5, 7, 9, and CCL8, and CXCL10; TNFSF9, CCL8, and CXCL10 were also significantly higher in T1DM than OW; no difference was observed between OW and CL. FcR stimulation induced similar responses across groups.

CONCLUSIONS

Leukocytes of T1DM children displayed exaggerated gene expression in response to ex vivo TCR induction of five key proinflammatory cytokines/chemokines. This elevated leukocyte gene expression may be one of the pathophysiological contributors to the development of vascular complications in T1DM.

Impaired immune responses in streptozotocin-induced type I diabetes in mice. Involvement of high glucose

Diabetes is widely believed to predispose to serious infections. However, the mechanisms linking diabetes and immunosuppression are not well defined. One potential mediator of the altered defence mechanisms is hyperglycaemia. It has been identified as the main factor contributing to the development of diseases associated with diabetes mellitus. In this study we analyse the immune response in diabetes and the direct effect of hyperglycaemia on T and B lymphocyte reactivity. Diabetes induced an early decrease in IgG levels in the secondary response. However, both primary responses against a T-cell-dependent or independent antigen were affected after 6 months of diabetes induction. T- and B- cell proliferation was only decreased at this time. To gain insight into the potential mechanisms involved, we evaluated the influence of hyperglycaemia over the immune response. Pre-incubation of lymph node and spleen cells in a high glucose (HG) containing medium led to a significant time- and dose-dependent decrease in T- and B-cell proliferation. This effect was associated with the presence of HG-derived supernatants. Still viable cells after HG exposition were able to improve their proliferative response when cultured with the mitogen in a fresh standard medium. HG diminished cell viability, increased apoptosis and induced oxidative stress in lymphocytes. These results indicate that HG concentrations can directly affect lymphoid cell growth. An increase in oxidative stress would be implicated in this deleterious effect. The possibility that prolonged exposure to pathologically HG concentrations would result in the immunosuppressive state observed in diabetes is also discussed.

Protein tyrosine phosphatase PTPN22 in human autoimmunity

The discovery that a single-nucleotide polymorphism (SNP) in lymphoid tyrosine phosphatase (LYP), encoded by the PTPN22 gene, is associated with type 1 diabetes (T1D) has now been verified by numerous studies and has been expanded to rheumatoid arthritis, juvenile rheumatoid arthritis (JRA), systemic lupus erythematosus, Graves' disease, generalized vitiligo and other human autoimmune diseases. In this paper, we discuss the association of PTPN22 with autoimmunity, the biochemistry of the PTPN22-encoded phosphatase, and the molecular mechanism(s) by which the disease-predisposing allele contributes to the development of human disease.

Reduced IFN-alpha secretion by blood dendritic cells in human diabetes

Characterization of dendritic cells (DC) in human diabetes has been restricted to monocyte-derived DC in type 1 diabetes, whose physiological relevance to endogenous DC is uncertain. Here, we provide the first report characterizing the phenotype and function of endogenous DC subsets in type 1 and type 2 diabetes. We show that DC subsets in each diabetic group exhibit normal properties concerning frequency and activation state, as determined using 4-color flow cytometry of whole blood cells. DC maturation is also intact as confirmed by their efficacious ability to stimulate T cell proliferation in an allogeneic MLR assay. Yet we found that DC are poor producers of IFN-alpha (P < 0.05) in human diabetes. IFN-alpha is a potent antiviral agent and therefore its reduced levels may interfere with T cell-mediated immune responses leading to increased susceptibility and persistence of infections in persons with diabetes.

Role of PTPN22 in type 1 diabetes and other autoimmune diseases

We recently discovered that a single-nucleotide polymorphism (SNP) in the lymphoid tyrosine phosphatase (LYP), encoded by the PTPN22 gene on chromosome 1p13, correlates strongly with the incidence of type 1 diabetes (T1D) in two independent populations. This findings has now been verified by numerous studies and it has been expanded to rheumatoid arthritis, juvenile rheumatoid arthritis, systemic lupus erythematosus, Graves' disease, generalized vitiligo and other autoimmune disease. Here we review the genetics of the SNP and its association with autoimmunity, discuss the function of the phosphatase in signaling, the biochemistry of the disease-predisposing allele, and the possible mechanisms by which PTPN22 contributes to the development of human disease.

NF-κB protects Behçet's disease T cells against CD95-induced apoptosis up-regulating antiapoptotic proteins

OBJECTIVE

To determine whether prolongation of the inflammatory reaction in patients with Behçet's disease (BD) is related to apoptosis resistance and is associated with the up-regulation of antiapoptotic factors.

METHODS

The percentage of cell death was evaluated by flow cytometry in peripheral blood mononuclear cells from 35 patients with BD and 30 healthy volunteers. The expression levels of antiapoptotic factors and NF-kappaB regulatory proteins were measured using Western blotting and immunohistochemical analyses. To down-regulate NF-kappaB nuclear translocation, BD T lymphocytes were exposed in vitro to thalidomide and subjected to transfection with NF-kappaB small interfering RNA.

RESULTS

Although CD95 is highly expressed in BD T cells, the absence of sensitivity to CD95-induced apoptosis observed may be attributable to the inhibitory action of antiapoptotic genes. Immunoblot analysis for major antiapoptotic proteins showed considerable up-regulation of the short form of cellular FLIP (cFLIP) and Bcl-x(L) in BD activated T cells, while levels of Bcl-2, caspase 3, and caspase 8 in activated T cells from patients with BD were comparable with those in activated T cells from normal donors. Moreover, expression of IKK and IkappaB was up-regulated, whereas NF-kappaB translocated to the nucleus in BD T cells, suggesting that NF-kappaB activation may modulate the expression of antiapoptotic genes. Interestingly, thalidomide and NF-kappaB small interfering RNA down-regulated cFLIP and Bcl-x(L) expression levels and sensitized BD activated T cells to CD95-induced apoptosis.

CONCLUSION

Taken together, these results indicate that NF-kappaB contributes to the regulation of the apoptosis-related factors and death receptors leading to apoptosis resistance in BD T cell subsets. Our results suggest that NF-kappaB plays a crucial role in the pathogenesis of BD, and that its pharmacologic control could represent a key strategy in modulating specific immune-mediated disease.

Defect in activation-induced cell death in non-obese diabetic (NOD) T lymphocytes

Activation-induced cell death (AICD) represents a major means of peripheral tolerance induction, eliminating effector cells. NOD mice, a widely used model for autoimmune diabetes, are characterized by high levels of circulating T lymphocytes and by resistance to several apoptosis-inducing signals. The aim of this study was to analyse AICD in peripheral NOD T lymphocytes. First, we demonstrated in an in vitro AICD model that NOD T lymphocytes are more resistant to AICD (64+/-2%) compared to non-autoimmune C57BL/6 T lymphocytes (73+/-2%), but also diabetes-resistant NOR T lymphocytes (76+/-3%, P<0.05). Moreover, both CD4(+)and CD8(+)subsets were affected. Analysis of the cellular and molecular pathways revealed lower caspase 8 levels, a central caspase proximally involved in the AICD-pathway (fluorescence of 258+/-47 in NOD vs. 441+/-16 in NOR and 414+/-61 in C57BL/6 T lymphocytes, P<0.05). Gene expression analysis using real-time RT-PCR additionally revealed low expression of Fas and FasL, the death receptor system activating caspase 8 and contributing to AICD. Additionally, low IL-2 levels, together with high TGFbeta and Bclx-L levels, confirm the presence of a NOD-specific AICD-resistance profile. In conclusion, we present cellular and molecular evidence for disturbed AICD mechanisms in NOD T lymphocytes. This resistance in AICD may contribute to defective tolerance induction to autoantigens in NOD mice.

Impaired primary immune response in type-1 diabetes. Functional impairment at the level of APCs and T-cells

We have recently described an impaired proliferative response of CD4(+) T-cells to primary antigens in patients with insulin-dependent diabetes mellitus (IDDM) [Clin. Immunol. 103 (2002) 249]. In order to further investigate possible mechanisms underlying this impairment, several factors known to be involved in the down-regulation of the immune response both at the level of APCs and CD4(+) T-cells were investigated: Monocyte-derived dendritic cells (MDDC) from IDDM patients were shown to express elevated amounts of CD86 (B7.2) (p=0.003) and reduced amounts of the adhesion molecule CD54 (ICAM-1) (p=0.03) on their cell surface compared to age-matched healthy controls and patients with non-insulin-dependent diabetes mellitus (NIDDM) as well as decreased SDS-PAGE stability of HLA-DQ and -DR peptide complexes directly isolated from the IDDM patients' peripheral blood mononuclear cells (PBMCs). Expression of CTLA-4 (CD152), known to be involved in the down-regulation of the immune response, was shown to be increased on CD4(+) T-cells from IDDM patients after exposure to the primary antigen KLH (keyhole limpet hemocyanin) presented by MDDC (p=0.0047). Likewise, purified CD4(+) T-cells from IDDM patients produced elevated levels of the cytokine TGF-beta1 after stimulation with immobilized monoclonal antibodies directed against CD3 and CD28 (p=0.014). When monocytes from IDDM patients were stimulated with lipopolysaccharide (LPS), an increased tendency to produce the inhibitory cytokine interleukin (IL)-10 (p=0.007) and the acute phase cytokine IL-6 (p=0.044) was observed, whereas the concentrations of tumor necrosis factor (TNF)-alpha, IL-1beta, and IL-12 were comparable to controls. Taken together, our data suggest that a deviation in the expression of certain molecules known to be involved in the peripheral control of the immune response is present in IDDM patients and is underlying the observed impairment of the primary immune response.

No association between lck gene polymorphisms and protein level in type 1 diabetes

We previously described a reduced expression of the protein tyrosine kinase Lck in T-cells from type 1 diabetic patients, the origin of which is still unknown. The human lck gene, located on chromosome 1p35-34.3, was evaluated as a candidate susceptibility gene for type 1 diabetes. A molecular scan of the sequence variations in the coding, the relevant promoter, and most of the intronic sequences of the lck gene (representing a total of 10.5 kb fragment) was performed in 187 Caucasian subjects including 91 type 1 diabetic patients and 96 normoglycemic control subjects. We identified 35 sequence variations, including one deletion and 34 single nucleotide polymorphisms (SNPs), 33 of them being new. Four variants were frequent but not significantly associated with diabetes or Lck protein level. Of the SNP variants, 11 were only found within the diabetic population and some were associated with low Lck protein levels. The low frequency of these polymorphisms did not permit any statistically significant correlations with the disease status, suggesting that the lck gene probably does not contribute to genetic susceptibility to type 1 diabetes.

Low proliferation capacity of lymphocytes from alloxan-diabetic rats: involvement of high glucose and tyrosine phosphorylation of Shc and IRS-1

The proliferation capacity of lymphocytes obtained from mesenteric lymph nodes of control and alloxan-diabetic (40 mg/kg) rats in response to concanavalin A (ConA) and lipopolysaccharide (LPS) stimuli was examined. Proliferation response of lymphocytes from diabetic rats was significantly reduced under Con A (43%) and LPS (46%) stimulation as compared with the control group. Insulin (166 microM) promoted a marked increase of lymphocyte proliferation (7.5-fold) in the control group and this response was much lower (2.6-fold) in lymphocyte from diabetic rats. Cells were also cultured in medium containing glucose at 5, 10 or 20 mM. High glucose concentration (20 mM) caused a marked inhibition of lymphocyte proliferation reaching the values of the diabetic group. In lymphocytes from control rats, the degree of Shc tyrosine phosphorylation was gradually increased, whereas that of cells from diabetic rats was much lower in response to insulin. In lymphocytes obtained from control rats, the tyrosine phosphorylation of IRS-1 was time-dependent on insulin. In cells from diabetic rats, the basal tyrosine phosphorylation of IRS-1 was higher than that of control rats, however, there was no further phosphorylation after insulin addition. We conclude that the response of lymphocyte proliferation from diabetic rats to Con A and LPS stimuli is decreased but insulin was able to promote a significant proliferative effect on these cells. Also, high glycemia in addition to the lack of insulin participates in the reduced proliferation capacity of lymphocytes from diabetic rats.

A defective NF-kappa B/RelB pathway in autoimmune-prone New Zealand black mice is associated with inefficient expansion of thymocyte and dendritic cells

New Zeland Black (NZB) mice develop an autoimmune disease involving an abnormal B cell response to peripheral self Ags. This disease is associated with defects in other cell types and thymic stromal organization. We present evidence that NZB cells of various lineages, including thymocytes, fibroblasts, and dendritic precursor cells, show impaired proliferation and enhanced cell death in culture upon stimulation compared with non-autoimmune-prone mice such as C57BL/6. This phenotype explains the reduced efficiency of maturation of bone marrow-derived dendritic cells and the loss of TNF- or IL-1-dependent thymocyte costimulation. Upon TNF-induced activation of NZB thymocytes, nuclear translocation and DNA binding of RelA- and RelB-dependent NF-kappaB heterodimers are significantly reduced. This phenotype has a transcriptional signature, since the NZB, but not the nonobese diabetic, thymic transcriptome shows striking similarities with that of RelB-deficient thymuses. This partial NF-kappaB deficiency detected upon activation by proinflammatory cytokines could explain the disorganization of thymic microenvironments in NZB mice. These combined effects might reduce the efficiency of central tolerance and expose apoptotic debris generated during inflammatory processes to self recognition.

Effect of hyperglycemia on the basal cytosolic free calcium level, calcium signal and tyrosine-phosphorylation in human T-cells

In this study, we investigated the effect of in vitro hyperglycemia on the function of human T-cells (Jurkat cells). Hyperglycemic conditions caused concentration-dependent elevation of basal cytosolic free calcium level and reduced calcium signal (activation capacity), either after ionomycin or monoclonal anti-CD3 antibody treatments. Similar changes were observed if cells were treated with the calcineurin inhibitor Cyclosporin-A. We found that tyrosine-phosphorylation after anti-CD3 treatment was also impaired. High glucose concentrations in the tissue culture medium are also associated with increased non-enzymatic glycation of T-cell proteins. We propose that the increased glycation of proteins involved in calcium transport and/or intracellular signal transduction in T-cells accounts for the abnormal calcium sequestration and calcium mediated signal transduction.

Impaired primary immune response in type-1 diabetes: results from a controlled vaccination study

Patients with diabetes have an increased risk for infections, but information on their adoptive immunity is incomplete and contradictory. Twenty patients with diabetes type-1 and 20 patients with type-2 diabetes were vaccinated with T-cell-dependent primary protein antigens (hepatitis A viral antigen, HAV; diphtheria toxoid) and a T-cell-independent polysaccharide antigen (pneumococcal polysaccharide). In parallel, the proliferative response of CD4+ T-cells to the primary protein antigens keyhole limpet hemocyanin (KLH) and sperm whale myoglobin (SWM) was measured in vitro using monocyte-derived dendritic cells (MDDC) as antigen-presenting cells. Compared to healthy controls, type-1 diabetes patients mounted a significantly impaired primary antibody response to hepatitis A vaccine (median HAV antibody titer after the first vaccination, 53 IU/L in diabetic patients vs 212 IU/L in the controls, P = 0.017) and diphtheria toxoid (median serum antibodies after vaccination, patients, 0.94 IU/ml, controls, 6.38 IU/ml, P = 0.004), while the response to pneumococcal polysaccharide was normal. Type-2 diabetes patients had a comparable metabolic dysregulation but showed a normal antibody response following vaccination, demonstrating that the effect was not due to hyperglycemia. Antigen-induced interferon-gamma and interleukin-13 release was reduced in type-1 diabetes patients, localizing the impairment to the level of antigen-presenting cell-T-cell interaction. In addition, the proliferative response of CD4+ T-cells derived from type-1 diabetes patients to KLH and SWM was significantly reduced (P < or = 0.01). FACS analysis of CD80 (B7.1), CD86 (B7.2), and HLA-DR expression on MDDC could not demonstrate significant differences in the expression of these molecules between type-1 and type-2 diabetes patients and healthy controls. An association of low HAV antibody response with HLA-DR3,4 expression in the patients was shown. Our results indicate that the primary antibody response to T-cell dependent antigens as well as the T-cell response to primary protein antigens is reduced in type-1 diabetes patients and that additional booster immunization can overcome the defect.

T-cell tolerance and autoimmune diabetes

Herein we describe the major signaling events that occur in T-cells upon T-cell receptor (TCR) engagement, and the mechanisms responsible for the induction of T-cell anergy that may ultimately lead to the development of immunospecific therapies in T-cell mediated autoimmune diseases. A new type of antigen presenting molecule (dimeric MHC class-II/peptide, DEF) endowed with antigen-specific immunomodulatory effects such as induction of Th2 polarization and T-cell anergy is also described as a potential antidiabetogenic agent. According to our preliminary results, the MHC II/peptide-based approach may provide rational grounds for further development of antigen-specific immunotherapeutic agents such as human-like MHC lI/peptide chimeras endowed with efficient down-regulatory effects in CD4 T-cell-mediated autoimmune diseases such as Type 1 diabetes, multiple sclerosis, primary biliary cirrhosis, and rheumatoid arthritis.

T-cell education in autoimmune diabetes: teachers and students

Type 1 diabetes mellitus is a classical example of a T-cell-mediated autoimmune disease. Several aberrations in immune regulation have been described in both human diabetes patients and animal models of type 1 diabetes. In this review, we summarize how proposed immune defects might be implicated in the loss of T-cell tolerance towards self in autoimmune diabetes in humans, nonobese diabetic (NOD) mice and Biobreeding (BB) rats. For this purpose, we will discuss the tolerance-inducing mechanisms that an autoreactive T cell should encounter from its genesis to its pathogenic role in the pancreas, in order of appearance. These comprise central tolerance mechanisms (i.e. positive and negative selection in the thymus) and those mechanisms operative in the periphery (i.e. activation-induced cell death and regulatory T cells).

Specific deficiency of p56lck expression in T lymphocytes from type 1 diabetic patients

Peripheral T lymphocyte activation in response to TCR/CD3 stimulation is reduced in type 1 diabetic patients. To explore the basis of this deficiency, a comprehensive analysis of the signal transduction pathway downstream of the TCR/CD3 complex was performed for a cohort of patients (n = 38). The main result of the study shows that T cell hyporesponsiveness is positively correlated with a reduced amount of p56(lck) in resting T lymphocytes. Upon CD3-mediated activation, this defect leads to a hypophosphorylation of the CD3zeta-chain and few other polypeptides without affecting the recruitment of ZAP70. Other downstream effectors of the TCR/CD3 transduction machinery, such as phosphatidylinositol 3-kinase p85alpha, p59(fyn), linker for activation of T cells (LAT), and phospholipase C-gamma1, are not affected. In some patients, the severity of this phenotypic deficit could be linked to low levels of p56(lck) mRNA and resulted in the failure to efficiently induce the expression of the CD69 early activation marker. We propose that a primary deficiency in human type 1 diabetes is a defect in TCR/CD3-mediated T cell activation due to the abnormal expression of the p56(lck) tyrosine kinase.

T cell signaling and autoimmune diabetes

Stimulation of the T-cell lymphocyte surface receptor (TCR) initiates a cascade of intracellular signaling events leading to proliferation, anergy, cytokine secretion, or apoptosis. In prediabetic NOD mice, T cell proliferative hyporesponsiveness has been correlated to decreased TCR-mediated signal transduction along the PKC/p21ras/p42mapk pathway. Limited data regarding T cell signaling defects are available in patients with autoimmune diabetes mellitus. Some but not all investigators have found decreased in vitro proliferative hyporesponsiveness to lectin mitogens or anti-CD3 mAb associated with impaired PKC activation and cytokine production. More recently, defective expression and function of the p21ras cascade was reported in these patients. Taken together, these data suggest that lymphocytes from animals and patients with autoimmune diabetes have defective TCR mediated signaling which may result in aberrant T cell activation and proliferation. This may lead to an imbalance of Th1/Th2 cytokine secretory pattern and thereby promote disease development.

Constitutive impaired TCR/CD3-mediated activation of T cells in IDDM patients co-exist with normal co-stimulation pathways

IDDM is a T cell-mediated autoimmune disease which is paradoxically associated with T cell functional deficiencies. The proliferative response of PBMC under CD3-, Vbeta2-, Vbeta8- and Vbeta7-stimulation was investigated in IDDM and NIDDM patients, non-diabetic first-degree relatives and control subjects. Despite normal surface expression of the TCR/CD3 complex, the TCR/CD3-mediated proliferation of PBMC from IDDM patients was significantly impaired compared to control subjects (P<0.05). This defect was specific for the autoimmune disease, constitutive and not linked to the class II MHC genotype, to metabolic disturbances or to presence of specific autoantibodies. Inefficient activation of T cells was not related to a lower capacity of CD28 to transduce co-stimulative signals because proliferative responses under CD2/CD28 stimulations were similar in IDDM and control groups. The IL-2/IL-2 receptor system was functional because unstimulated PBMC proliferated in response to increasing amounts of IL-2. Nevertheless, despite normal expression of CD25, addition of IL-2 did not normalize the proliferative defect linked to IDDM. In conclusion, excluding a faulty co-stimulation pathway, these results are in favour of a constitutive defect in the CD3/TCR transduction machinery, increasing sensitivity to apoptosis or anergy in T cells from IDDM patients.

Defective activation of p21ras in peripheral blood mononuclear cells from patients with insulin dependent diabetes mellitus

We previously reported that a decreased TCR mediated activity of the GTP-GDP binding p21ras protooncogene is associated with prediabetes in non-obese diabetic (NOD) mice. Furthermore, prevention of autoimmune diabetes is associated with reversal of the p21ras signaling defect in NOD T cells. Based on these animal studies we determined the activation of p21ras in PBMC from patients with Insulin Dependent Diabetes Mellitus (IDDM), Non-Insulin Dependent Diabetes Mellitus (NIDDM) and normal healthy controls. Stimulation by PHA induced a decrease of 3.7 +/- 1.4% and an increase of 2.44 +/- 2.3%, p < 0.02 and 2.6 +/- 1.6%,p < 0.003 in the basal unstimulated p21ras activity in the IDDM, NIDDM and normal control groups, respectively. Expression of p21ras and its regulatory elements, the GTPase activating protein p120ras-GAP and the guanine nucleotide releasing factor (GNRF) hSOS, was comparable in the three groups. The in vitro proliferative response to PHA was comparable in the IDDM and control groups: stimulation index (SI) of 8.6 +/- 2.5 and 9.4 +/- 3.5 respectively, p < 0.44. No correlations were found in the IDDM patients between the degree of p21ras activation and the mitogen induced in vitro proliferative response or the various clinical parameters including age, gender, disease duration, daily insulin requirements and metabolic control. Taken together these data indicate that PBMC from IDDM patients are characterized by a persistent impairment in the activation of their p21ras. They also suggest that p21ras stimulated activity is a sensitive and independent parameter of PBMC activation in these patients.

Aberrant prostaglandin synthase 2 expression defines an antigen-presenting cell defect for insulin-dependent diabetes mellitus

Prostaglandins (PGs) are lipid molecules that profoundly affect cellular processes including inflammation and immune response. Pathways contributing to PG output are highly regulated in antigen-presenting cells such as macrophages and monocytes, which produce large quantities of these molecules upon activation. In this report, we demonstrate aberrant constitutive expression of the normally inducible cyclooxygenase PG synthase 2 (PGS(2)/ COX-2) in nonactivated monocytes of humans with insulin-dependent diabetes mellitus (IDDM) and those with islet autoantibodies at increased risk of developing this disease. Constitutive PGS(2) appears to characterize a high risk for diabetes as it correlates with and predicts a low first-phase insulin response in autoantibody-positive subjects. Abnormal PGS(2) expression in at-risk subjects affected immune response in vitro, as the presence of a specific PGS(2) inhibitor, NS398, significantly increased IL-2 receptor alpha-chain (CD25) expression on phytohemagglutinin-stimulated T cells. The effect of PGS(2) on CD25 expression was most profound in subjects expressing both DR04 and DQbeta0302 high-risk alleles, suggesting that this cyclooxygenase interacts with diabetes-associated MHC class II antigens to limit T-cell activation. These results indicate that constitutive PGS(2) expression in monocytes defines an antigen-presenting cell defect affecting immune response, and that this expression is a novel cell-associated risk marker for IDDM.

The quantitative and qualitative defect of CD4+ CD45RO+ memory-type T cells are involved in the abnormality of TH1 immunity in atopic dermatitis patients

Peripheral blood mononuclear cells (PBMCs) obtained from atopic dermatitis (AD) patients produced low levels of IFN-gamma in response to Dermatophagoides farinae antigen (Der f Ag) plus IL-2 or OKT3 MoAb in contrast with PBMCs obtained from healthy donors. The reduced IFN-gamma production in AD patients' T cells appeared to be derived from the defect of CD4+ T cells but not CD8+ T cells. Indeed, from the cytoplasmic staining analysis of cytokines, it was demonstrated that the frequency of IFN-gamma producing CD4+ T cells (TH1 cells) in AD patients was markedly lower than that of healthy donors. From the phenotypic analysis using flow cytometry, it was also found that the number of CD4+ CD45RO+ memory type T cells was significantly reduced in AD patients compared with that of healthy donors. In addition to quantitative defect of memory type CD4+ T cells, functional defect of CD4+ CD45RO+ memory type T cells was also demonstrated in AD patients. Enriched CD4+ CD45RO+ T cells obtained from AD patients, who exhibited greatly reduced delayed-type hypersensitivity (DTH) response in tuberculin test, showed no significant TH1 immunity in terms of IFN-gamma production by stimulation with OKT3 MoAb or purified protein derivative (PPD). Thus, the immunological abnormality of TH1 immunity in AD patients appeared to be induced in concomitant with both the quantitative and qualitative defect of memory type CD4+ T cells.

Autoimmune enteropathy with distinct mucosal features in T-cell activation deficiency: the contribution of T cells to the mucosal lesion

BACKGROUND

Autoimmune enteropathy is normally characterised by crypt hyperplastic villous atrophy with enterocyte autoantibodies, activation of mucosal lymphocytes and increased epithelial HLA-DR. This case involved a severely affected Portuguese infant who was found to have lymphocyte activation deficiency and demonstrated correspondingly distinct mucosal features.

METHODS

A female infant of nonconsanguineous parents was treated for vomiting and diarrhoea, first with milk exclusion and then with parenteral nutrition. Lymphocyte subsets and immunoglobulin concentrations were normal, but in vitro testing showed no activation in response to phytohaemagglutinin, Candida, or purified protein derivative, although the response to interleukin (IL)-2 was intact. Interleukin-2 deficiency was excluded. Analysis of jejunal biopsy specimens revealed only mild villous blunting with absent goblet cells, normal epithelial proliferation, and no crypt hyperplasia. The dense infiltrate of CD8+ and CD4+ T lymphocytes showed normal CD2 and CD3 expression but no activation or proliferation markers. HLA-DR was not increased on epithelium or lymphocytes. Thus, in addition to in vitro evidence for lymphocyte activation deficiency, the mucosal specimens showed no evidence of in situ T-cell activation.

RESULTS

After development of overwhelming septicaemia, the patient died at 18 months, just before a planned bone marrow transplant.

CONCLUSIONS

These findings confirm significant heterogeneity within autoimmune enteropathy. Formal immune function testing should be performed in all affected infants to identify T-cell activation deficiencies. The distinct mucosal findings suggest that activated T cells usually induce the crypt hyperplastic villous atrophy characteristic of classic autoimmune enteropathy.

Multidose streptozotocin induction of diabetes in BALB/cBy mice induces a T cell proliferation defect in thymocytes which is reversible by interleukin-4

Thymic T cell function in streptozotocin-treated (STZ) diabetic mice has been examined. STZ administration suppresses thymic T cell proliferation in response to mitogen stimulation in vitro. Secretion of IL-4 was dramatically reduced; however, secretion of IL-2 or IFN-gamma was not significantly inhibited. RT-PCR analysis of thymocyte RNA revealed that levels of IL-4 mRNA were dramatically decreased in STZ-treated mice. Levels of mRNA encoding IFN-gamma were similar, but the appearance was delayed in thymocytes derived from STZ-treated mice, implying differential regulation of IL-4 and IFN-gamma. Defective thymocyte proliferation was partially restored by exposure to IL-2 in vitro; however, IL-4 completely reversed the STZ-induced defect. Administration in vivo of IL-4 before STZ treatment reversed the STZ-induced thymocyte proliferation defect and prevented both pancreatic islet destruction and hyperglycemia. Thymocyte cell surface differentiation markers were not appreciably different from control mice. Collectively these experiments suggest that STZ treatment of mice reduces expression of IL-4 which is associated with development of autoimmune diabetes.

Decreased secretion of Th2 cytokines precedes Up-regulated and delayed secretion of Th1 cytokines in activated peripheral blood mononuclear cells from patients with insulin-dependent diabetes mellitus

Recent evidence suggests that autoimmune animal diabetes is associated with an imbalance between the Th1 and Th2 arms of the cellular immune system. However, limited data is available regarding the Th1/Th2 imbalance in human Insulin dependent diabetes mellitus (IDDM) patients. Therefore, we examined the peak levels, secretory pattern and total cytokine production (calculated as the area under the curve, AUC) of the Th1 cytokines, IL-2 and IFN-gamma, and Th2 cytokines, IL-4 and IL-10, from stimulated peripheral blood mononuclear cells, from 17 IDDM patients and 24 normal controls. In contrast to controls, diabetic patients were characterized by an early, uniformly low secretion of Th2 cytokines, followed by a late increased secretion of Th1 cytokines. This resulted in significant differences in secretory patterns of IFN-gammaIL-2, IL-4 and IL-10 between the two groups; P<0.001, P<0.005, P<0.005 and P<0.001, respectively. No correlation was found in the diabetic patients between any profiles of the cytokines and their various clinical parameters, including age, gender, disease duration, insulin requirements or glycated hemoglobin levels. In conclusion, our data provides the first comprehensive evidence for an independent and persistent impairment of both Th1 and Th2 cytokine secretory patterns in IDDM patients.

The influence of surgical stress on T cells: enhancement of early phase lymphocyte activation

For the control of postoperative infection, it may be important to understand the possible influences of surgical stress on the host immune system. To this end, we examined how the early phase of lymphocyte activation was affected in patients after major surgery (eight patients with esophageal carcinoma and six undergoing cardiac surgery) using a flow cytometric assay based on expression of the early activation antigen, CD69. Freshly isolated T cell in preoperative and postoperative samples did not express CD69. When peripheral blood mononuclear cells were stimulated in vitro, the expression of CD69 was greatly enhanced in both CD4 and CD8 T cells, compared with the preoperative samples. The proportion of de novo CD69-expressing cells in the CD4 subset was approximately 3 times (Postoperative Day 1) and 4 times (Postoperative Days 2, 3, 5, and 7) greater than those preoperatively, whereas the proportion of de novo CD69-expressing cells in the CD8 subset was approximately 1.5 times (Postoperative Days 2 and 5) and 2 times (Postoperative Day 3) greater than those preoperatively. The proportion of CD69+ cells was significantly greater in the CD4+ subset than in the CD8+ subset during the postoperative period.

IMPLICATIONS

Our results show that major surgical stress enhances the early phase of lymphocyte activation. The augmentation of activation was greater in CD4 (helper) T cells than in CD8 (cytotoxic) T cells.

Increased CD69 and human leukocyte antigen-DR expression on T lymphocytes in insulin-dependent diabetes mellitus of long standing

To better define prevailing activation of circulating T cell subsets in insulin-dependent diabetes mellitus (IDDM) of recent onset (DM; n = 31; median age +/- SD, 28 +/- 6.9 yr) and of long standing (DML; n = 27; age, 33 +/- 10.4 yr; median duration of disease, 105 months), CD4+ and CD8+ T cells were analyzed to determine their naive and memory subsets as well as their expression of human leukocyte antigen (HLA)-DR, interleukin-2 receptor alpha-chain (CD25), and CD69 by three-color flow cytometry. Twenty-six healthy subjects (HS; age, 32.0 +/- 8.2 yr) served as controls. No deviation was seen in either IDDM group compared to HS in CD25 expression on CD4+ or CD8+ cells or in their CD45RA+ or CD45RA- subsets. HLA-DR expression, however, was increased (P < 0.05) in total CD8+ cells and CD45RA+ cells, with CD45RA- CD8+ cells joining the prevailing pattern only in DML. Among CD4+ cells, increased expression of HLA-DR molecules was restricted to total and CD45RA- cells in DML. CD69 expression did not differ between IDDM and HS, but differed between DML (CD4+, CD8+, and CD45RA- CD4+) and DM only. In conclusion, our data demonstrate that HLA-DR expression in IDDM is restricted to memory cells (CD45RA-) among CD4+ cells in DML and is more markedly confined to naive (CD45RA+) than to memory CD8+ cells, whereas the early activation antigen CD69 is more readily expressed in DML than in DM. The observed activation of circulating T cells suggests an ongoing immune process in IDDM both at clinical manifestation and after long duration.

Improved IL-2 detection for determination of helper T lymphocyte precursor frequency in limiting dilution assay

In the context of allogeneic bone marrow transplantation, an accurate estimate of the risk of developing graft-versus-host disease (GVHD) is of major interest. The pre-transplant frequency of donor's helper T-lymphocyte precursors (HTLp) directed against host's antigens may be helpful in predicting this risk. This technique relies on an indirect measurement of interleukin-2 (IL-2) secreted by the HTLp, as assessed by the proliferation of an IL-2 dependent cell line. Many authors use the murine CTLL-2 cell line in this assay, but these cells do not respond to the presence of minute amounts of IL-2 in the culture medium, and thus do not discriminate between the absence or the presence of very low levels of IL-2. We therefore decided to compare CTLL-2 with another IL-2 dependent cell line, the murine A9.12 cell line. A comparison was made using serial dilutions of recombinant human IL-2, limiting dilutions of baby hamster kidney (BHK) cells transfected with human IL-2 gene and in the context of clinical tests performed for the detection of pre-transplant HTLp. Both the sensitivity and reliability of the tests were better using A9.12. We conclude that the A9.12 cell line might be a more suitable tool for pre-transplant HTLp determinations before allogeneic bone marrow transplantation or whenever low IL-2 levels are to be measured.

Apoptosis and ageing

Stimulation of T cells from aged individuals leads to different kinds and/or size of responses if compared with the responses of T cells obtained from young individuals. In fact elderly is associated with a progressive decline of immune response besides an increasing incidence of autoimmune phenomena. These differences might be the result of modified cellular mechanisms controlling the immune system in the course of ageing. The apoptotic deletion of activated T cells has been proposed as the key mechanism to maintain T cell homeostasis, and in this respect CD95 (Fas antigen) seems to play a major role in this course of events. In this study we show that just collected lymphocytes from old subjects displayed an increased expression of the apoptosis molecule CD95. The expression of CD95 and the spontaneous apoptosis showed the same trend. In fact the percentage of apoptotic cells in blood collected from old subjects was enhanced too. The lymphocyte subpopulation analysis by flow cytometry did not show significant changes in T subset percentages between old and young subjects. Moreover mononuclear cells obtained from aged individuals underwent apoptosis in culture in response to a single stimulation with mitogen or anti-CD3, more than mononuclear cells from young controls. To gain insight into mechanisms of this increased apoptosis, experiments were performed to evaluate the behaviors of lymphocytes from old and young donors in respect of interleukin-2 (IL-2) rescue from apoptosis. Results show that IL-2 rescued only a little fraction of cells of old donors from apoptosis when activated by anti-CD3 and that this effect was not related to a different expression of CD95. Thus, during the course of ageing the different regulation of T cell homeostasis might be also explained by the modified proneness of lymphocytes to undergo apoptosis. The contemporaneous demonstration of a reduced Ca2+ influx in lymphoid cells of these subjects allows to suppose that multiple defects play a role in the pathogenesis of immunosenescence.

Increased intracellular calcium and altered phorbol dibutyrate binding to intact platelets in young subjects with insulin-dependent and non-insulin-dependent diabetes mellitus

Intracellular calcium ([Ca2+]i) and phorbol ester binding were studied in intact platelets of young patients with insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetes mellitus. Our objective was to evaluate disturbances in calcium regulation and signal transduction in platelets of diabetics. [Ca2+]i in platelets of the IDDM group (135 +/- 20 nmol/L) under basal conditions was significantly higher than that of the control group (81 +/- 8 nmol/L, P = .019), whereas at 60 seconds after stimulation with 0.1 National Institutes of Health (NIH) U/mL thrombin, [Ca2+]i in the NIDDM group (484 +/- 36 nmol/L) was significantly higher than that of the controls (347 +/- 22 nmol/L, P = .003) and IDDM group (360 +/- 45 nmol/L, P = .04), respectively. Phorbol 12,13-dibutyrate (PdBu) maximal binding capacity (Bmax) in the IDDM group was significantly lower than that in the control group either under basal conditions or after stimulation with thrombin (P = .0034 and P = .015, respectively). Bmax in the NIDDM group was significantly lower than that in the controls only after stimulation with thrombin (P = .047). The Kd for PdBu of the IDDM group was lower than that of the control group under basal conditions (P = .017). When analyzing the pooled data of all subjects, a significant correlation was observed between Bmax and Kd (under basal conditions, r = .544, P < .0001; after stimulation, r = .601, P < .0001). Our results support the idea that the increased affinity for PdBu may compensate for the decreased binding capacity. We interpret the data as indicating that the change in the binding of phorbol ester to protein kinase C (PKC) units may result in an altered PKC/calcium interaction in the pathogenesis of diabetes mellitus. Our study indicates that such metabolic derangements of [Ca2+]i have already been developing in young diabetic patients.

In vitro T cell activation in elderly individuals: failure in CD69 and CD71 expression

A large number of T cell dysfunctions have been observed in the elderly. The most widely observed is the inability of these cells to proliferate at a level comparable to T cells from young individuals after stimulation by mitogens. To better characterize T cell impairment, we have focused on the in vitro T cell activation, analyzing by flow cytometry the activation molecules CD69 and CD71 on mitogen-stimulated lymphocytes from young and elderly subjects. The results show that the percentages of CD69+ and CD71 + T cells were significantly decreased in cultures from elderly subjects when compared to values obtained culturing cells from young individuals. The differences observed seem not due to differences in CD4 and CD8 rates in the "old' cells that underwent activation, since, following activation, the pattern of CD4 and CD8 phenotypes was the same in both groups of subjects. Signals from CD69 are relevant in controlling cytokine gene expression because its stimulation leads to interleukin-2 production and increases its receptor expression. The interaction of this cytokine with its cellular receptor is an essential requirement for T lymphocytes to express CD71 and to start proliferation. Thus, a key role in the age-associated impairment of T cell activation could be played by an ineffective modulation of CD69 expression suggesting a defect in the signal transduction pathway of the T cell receptor-CD3 complex in elderly.

Defective expression of the apoptosis-inducing CD95 (Fas/APO-1) molecule on T and B cells in IDDM

Triggering of CD95 (Fas/APO-1) cell surface receptors regulates the elimination of autoreactive T and B lymphocytes through a mechanism of cell suicide called apoptosis. Three different mutations involving CD95 or its ligand are responsible for induction of autoimmunity in susceptible mouse strains. To determine whether a defect involving the CD95 receptor is associated with human insulin-dependent diabetes mellitus (IDDM), we have studied the expression of CD95 on peripheral blood mononuclear cells from IDDM patients at different stages of the disease. Three-colour flow cytometry and mean fluorescence analysis showed that T and B lymphocytes from newly diagnosed IDDM and patients with long-standing disease, and subjects at high risk of developing the disease were highly defective in CD95 expression (p < 0.001), whereas monocytes from all the groups studied expressed normal amounts of CD95 molecules on their cell surface. T-cell subset analysis showed that the impairment of CD95 expression in IDDM patients and high-risk subjects involved both CD3+ CD4+ (p < 0.001) and CD3+ CD8+ cells (p range: < 0.01-0.001), suggesting that this alteration concerns both helper and cytotoxic T cells. Moreover, after activation in vitro with anti-CD3 monoclonal antibody, T cells from newly diagnosed IDDM patients maintained a reduced CD95 expression during the entire cell culture period (24-72 h) in comparison to the control population (p < 0.001). In conclusion, we found a reduced expression of the apoptosis-inducing CD95 receptor on T and B lymphocytes of individuals with clinical and preclinical IDDM. We hypothesize that this defective expression may impair the capacity of autoreactive lymphocytes to undergo CD95-mediated apoptosis, contributing to the lack of control on beta-cell specific B- and T-cell clones.

Low bcl-2 expression and increased spontaneous apoptosis in T-lymphocytes from newly-diagnosed IDDM patients

The bcl-2 gene product has been shown to regulate apoptotic cell death, and its dysregulation has been shown to induce several abnormalities in the immune system. No data exist regarding bcl-2 expression in autoimmune diseases, such as human insulin-dependent diabetes mellitus (IDDM). We investigated bcl-2 protein expression by testing T lymphocytes from 15 newly-diagnosed (< 3 weeks) IDDM patients in comparison to 10 age-matched control subjects. The expression of bcl-2 on CD3+ lymphocyte subsets was investigated after membrane permeabilization by two- or three-colour immunofluorescence. When the percentage and mean fluorescence intensity (MFI) of bcl-2+/CD3+ cells from normal individuals and patients were compared, we found that bcl-2 expression within the CD3+ and CD4+ CD45R0+ T-cell populations was reduced significantly in IDDM patients (46.8 +/- 15.4 vs 79.6 +/- 11.7; 25.7 +/- 3.8 vs 47.15 +/- 5.7, respectively; p < 0.001). To establish whether low bcl-2 expression in T cells from newly-diagnosed patients reflects their susceptibility to death by an apoptotic process, we also evaluated DNA staining with propidium iodide in CD3+ lymphocyte suspension after a (24-72 h) culture period (spontaneous apoptosis). We found that IDDM patients have higher levels of spontaneous apoptosis (mean +/- SEM: 24 h = 4.6 +/- 0.8; 48 h = 9.9 +/- 1; 72 h = 12.8 +/- 1.1) than control subjects (24 h = 1.8 +/- 0.4; 48 h = 4.6 +/- 0.4; 72 h = 5.7 +/- 0.3; p < 0.02-0.001). Our study suggests that recent onset IDDM is characterised by reduced bcl-2 expression, which in turn may be associated with the increased spontaneous apoptosis we observed.

T-cell activation in HLA-B8, DR3-positive individuals. Early antigen expression defect in vitro

The HLA-B8, DR3 haplotype is overrepresented in several autoimmune diseases, implying that genes predisposing to these disorders are linked to this haplotype. In the patients affected by these diseases, as well as in healthy HLA-B8, DR3 individuals, various dysfunctions reflecting an impairment of T-cell activation have been found. To better characterize T-cell impairment of HLA-B8, DR3-positive healthy individuals, we analyzed the surface expression of early (CD69) and late (CD71) activation phenotypes. MNC cultures were stimulated with PHA and used for T-cell phenotyping by flow cytometry analysis. The results showed that the percentage of CD69+ T cells was significantly decreased in MNC from HLA-B8, DR3+ subjects. This defect was detected in cell cultures from all subjects studied, but it attained significance only in females in the early hours after stimulation. The difference in CD69 expression between HLA-B8, DR3-positive individuals and -negative ones was not due to differences in CD4 and CD8 ratios in the HLA-B8, DR3 cells that underwent activation, as following activation the pattern of CD4 and CD8 antigen expression was the same in both groups of subjects. Concerning the late antigen CD71, no significant difference in percentage was observed between T lymphocytes from HLA-B8, DR3+ and HLA-B8, DR3- subjects at all the times studied. The analysis of the requirements for CD69 expression has suggested that sustained PKC activation and an increase of intracellular CA2+ could be responsible for TCR/CD3-mediated CD69 induction. Thus, present data suggest a defect in the signal transduction pathway of the TCR/CD3 complex.(ABSTRACT TRUNCATED AT 250 WORDS)