Decreased number of T cells bearing TCR rearrangement excision circles (TREC) in active recent onset systemic lupus erythematosus

T-cell senescence: A crucial player in autoimmune diseases

Senescent T cells are proliferative disabled lymphocytes that lack antigen-specific responses. The development of T-cell senescence in autoimmune diseases contributes to immunological disorders and disease progression. Senescent T cells lack costimulatory markers with the reduction of T cell receptor repertoire and the uptake of natural killer cell receptors. Senescent T cells exert cytotoxic effects through the expression of perforin, granzymes, tumor necrosis factor, and other molecules without the antigen-presenting process. DNA damage accumulation, telomere damage, and limited DNA repair capacity are important features of senescent T cells. Impaired mitochondrial function and accumulation of reactive oxygen species contribute to T cell senescence. Alleviation of T-cell senescence could provide potential targets for the treatment of autoimmune diseases.

Exploiting Signal Joint T Cell Receptor Excision Circle to Investigate the Impact of COVID-19 and Autoimmune Diseases on Age Prediction and Immunosenescence

Signal joint T cell receptor excision circles (sjTRECs) are a promising marker for age estimation and immunosenescence in different ethnic groups. Several limitations are expected to overshadow their use as accurate markers for age prediction. The current study was conducted to determine the influence of immunologic disorders, such as autoimmune diseases and COVID-19, on the accuracy of sjTRECs as molecular markers for age estimation and immunosenescence among living Egyptians. Peripheral blood sjTRECs level was measured by qPCR in 90 autoimmune patients, 58 COVID-19 patients, and 85 healthy controls. The mean dCt values were significantly (p = 0.0002) different between the three groups, with the highest values in healthy subjects, followed by autoimmune and COVID-19 patients. A significant negative correlation was identified between the sjTRECs levels and ages in all studied cases. There were significant positive correlations between chronological age and predicted age for healthy individuals, autoimmune, and COVID-19 patients with mean absolute deviations (MAD) of 9.40, 11.04, and 9.71, respectively. The two patients' groups exhibited early immunosenescence, which was more noticeable among the young adults with COVID-19 and autoimmune patients of age range (18-49 years). Autoimmunity may represent a critical factor impacting the accuracy of sjTRECs quantitation for age prediction.

Assessment of Thymic Output Dynamics After in utero Infection of Mice With Coxsackievirus B4

The thymus is the main organ of the lymphatic system, in which T cells undergo a rigorous selection to ensure that their receptors (TCRs) will be functional and will not react against the self. Genes encoding for TCR chains are fragmented and must be rearranged by a process of somatic recombination generating TCR rearrangement excision circles (TRECs). We recently documented coxsackievirus B4 (CV-B4) infection of Swiss albino mouse thymus in the course of in utero transmission. In the current study, we intended to evaluate thymic output in this experimental model. For this purpose, pregnant Swiss albino mice were inoculated with CV-B4 at day 10 or 17 of gestation, and thymus and spleen were sampled from offspring at different time points and then subjected to quantification of TREC molecules and Ptk7 gene expression. Results showed a pronounced effect of in utero CV-B4 infection on the thymus with an increase in the cellularity and, consequently, the weight of the organ. sj and DβTREC analysis, by real-time PCR, revealed a significant decrease following CV-B4 infection compared to controls, a decrease which gets worse as time goes by, both in the thymus and in the periphery. Those observations reflect a disturbance in the export of T cells to the periphery and their accumulation within the thymus. The evaluation of Ptk7 transcripts in the thymus, for its part, showed a decrease in expression, especially following an infection at day 10 of gestation, which supports the hypothesis of T cell accumulation in a mature stage in the thymus. The various effects observed correlate either negatively or positively with the viral load in the thymus and spleen. Disruption in thymic export may indeed interfere with T cell maturation. We speculate that this may lead to a premature release of T cells and the possibility of circulating autoreactive or proliferation-impaired T cell clones.

Regenerating Immunotolerance in Multiple Sclerosis with Autologous Hematopoietic Stem Cell Transplant

Multiple sclerosis (MS) is an inflammatory disorder of the central nervous system where evidence implicates an aberrant adaptive immune response in the accrual of neurological disability. The inflammatory phase of the disease responds to immunomodulation to varying degrees of efficacy; however, no therapy has been proven to arrest progression of disability. Recently, more intensive therapies, including immunoablation with autologous hematopoietic stem cell transplantation (AHSCT), have been offered as a treatment option to retard inflammatory disease, prior to patients becoming irreversibly disabled. Empirical clinical observations support the notion that the immune reconstitution (IR) that occurs following AHSCT is associated with a sustained therapeutic benefit; however, neither the pathogenesis of MS nor the mechanism by which AHSCT results in a therapeutic benefit has been clearly delineated. Although the antigenic target of the aberrant immune response in MS is not defined, accumulated data suggest that IR following AHSCT results in an immunotolerant state through deletion of pathogenic clones by a combination of direct ablation and induction of a lymphopenic state driving replicative senescence and clonal attrition. Restoration of immunoregulation is evidenced by changes in regulatory T cell populations following AHSCT and normalization of genetic signatures of immune homeostasis. Furthermore, some evidence exists that AHSCT may induce a rebooting of thymic function and regeneration of a diversified naïve T cell repertoire equipped to appropriately modulate the immune system in response to future antigenic challenge. In this review, we discuss the immunological mechanisms of IR therapies, focusing on AHSCT, as a means of recalibrating the dysfunctional immune response observed in MS.

Activated T cells enhance interferon-α production by plasmacytoid dendritic cells stimulated with RNA-containing immune complexes

OBJECTIVES

Patients with systemic lupus erythematosus (SLE) have an ongoing interferon-α (IFN-α) production by plasmacytoid dendritic cells (pDCs). We investigated whether T cells can promote IFN-α production by pDCs.

METHODS

Human pDCs were stimulated with immune complexes (ICs) containing U1 small nuclear ribonucleic proteins particles and SLE-IgG (RNA-IC) in the presence of T cells or T cell supernatants. T cells were activated by anti-CD3/CD28 antibodies or in a mixed leucocyte reaction. IFN-α and other cytokines were determined in culture supernatants or patient sera with immunoassays. The effect of interleukin (IL) 3 and granulocyte-macrophage-colony-stimulating factor (GM-CSF) on pDCs was examined by the use of antibodies, and the expression of CD80/CD86 was determined using flow cytometry.

RESULTS

Activated T cells and supernatants from activated T cells increased IFN-α production by >20-fold. The stimulatory effect of T cell supernatants was reduced after depletion of GM-CSF (81%) or by blocking the GM-CSF receptor (55%-81%). Supernatant from activated T cells, furthermore, increased the frequency of CD80 and CD86 expressing pDCs stimulated with RNA-IC from 6% to 35% (p<0.05) and from 10% to 26% (p<0.01), respectively. Activated SLE T cells enhanced IFN-α production to the same extent as T cells from healthy individuals and a subset of patients with SLE had increased serum levels of GM-CSF.

CONCLUSIONS

Activated T cells enhance IFN-α production by RNA-IC stimulated pDCs via GM-CSF and induce pDC maturation. Given the increased serum levels of GM-CSF in a subset of patients with SLE, these findings suggest that activated T cells may upregulate type I IFN production in SLE.

Increased concentration of T-cell receptor rearrangement excision circles (TREC) in peripheral blood in Graves' disease

BACKGROUND

T-cell receptor rearrangement excision circles (TREC) are circular DNA molecules generated during T-cell maturation in the thymus. Recent studies suggested that a decreased TREC concentration in peripheral blood may be a general feature of autoimmunity. Our purpose was to assess the TREC concentration in Graves' disease (GD).

METHODS

TREC concentration was assessed by real time PCR in DNA samples isolated from peripheral blood leucocytes among younger (n = 94, age range 6-29 years) and older patients with GD (n = 93, age range 57-80 years) and age-matched controls (n = 206).

RESULTS

TREC concentration decreased with age in all subjects, but it was significantly higher in GD compared with controls (P = 9·4 × 10(-10) ). TREC concentration was higher (P = 0·0038) in hyperthyroid (n = 78) than euthyroid (n = 82) patients with GD, but in both groups, it remained increased relative to controls (P = 2·2 × 10(-11) and P = 4·4 ×10(-7) , respectively).

CONCLUSIONS

Patients with GD, particularly those with hyperthyroidism, have increased concentration of TREC which may suggest increased rather than decreased thymic activity. Thus, GD does not follow the paradigm suggested for other autoimmune disorders which links autoimmunity with thymic senescence.

Umbilical cord-derived mesenchymal stem cells regulate thymic epithelial cell development and function in Foxn1(-/-) mice

Thymic microenvironments are essential for the maturation of thymocytes, which can be anatomically compartmentalized into cortical and medullar regions. The absence of the gene encoding the transcription factor forkhead box n1 (Foxn1) causes epithelial differentiation to stall in the precursor stage, resulting in the formation of an abnormal thymus. In this study, we used human umbilical cord-derived mesenchymal stem cells (UC-MSCs) to treat Foxn1(-/-) mice, and then analyzed the maturation and distribution of thymic epithelial cells in the Foxn1(-/-) thymic rudiment and the thymopoiesis of this newly developed rudiment. Our data showed a well-organized cortex-medulla architecture and an obvious improvement in the maturation of thymic epithelial cells along with the appearance of UEA-1(+)MHCII(hi) thymic epithelial cells in the rudiment. We further demonstrated improved thymopoiesis and the enhanced export of mature T cells with increased numbers of regulatory T cells into the peripheral blood. Furthermore, we observed that MSCs can engraft into thymic tissue and express many cytokines or proteins, particularly keratinocyte growth factor (KGF) and CD248, which are essential for thymic development. Collectively, our data identified a new mechanism for MSCs, which may provide a proper microenvironment for the reconstitution and functional maturation of the thymus in Foxn1(-/-) mice. Additionally, we elicited additional insights into the therapeutic efficacy of MSCs in several autoimmune diseases.

Late-onset myasthenia gravis - CTLA4(low) genotype association and low-for-age thymic output of naïve T cells

Late-onset myasthenia gravis (LOMG) has become the largest MG subgroup, but the underlying pathogenetic mechanisms remain mysterious. Among the few etiological clues are the almost unique serologic parallels between LOMG and thymoma-associated MG (TAMG), notably autoantibodies against acetylcholine receptors, titin, ryanodine receptor, type I interferons or IL-12. This is why we checked LOMG patients for two further peculiar features of TAMG - its associations with the CTLA4(high/gain-of-function) +49A/A genotype and with increased thymic export of naïve T cells into the blood, possibly after defective negative selection in AIRE-deficient thymomas. We analyzed genomic DNA from 116 Caucasian LOMG patients for CTLA4 alleles by PCR/restriction fragment length polymorphism, and blood mononuclear cells for recent thymic emigrants by quantitative PCR for T cell receptor excision circles. In sharp contrast with TAMG, we now find that: i) CTLA4(low) +49G(+) genotypes were more frequent (p = 0.0029) among the 69 LOMG patients with age at onset ≥60 years compared with 172 healthy controls; ii) thymic export of naïve T cells from the non-neoplastic thymuses of 36 LOMG patients was lower (p = 0.0058) at diagnosis than in 77 age-matched controls. These new findings are important because they suggest distinct initiating mechanisms in TAMG and LOMG and hint at aberrant immuno-regulation in the periphery in LOMG. We therefore propose alternate defects in central thymic or peripheral tolerance induction in TAMG and LOMG converging on similar final outcomes. In addition, our data support a 60-year-threshold for onset of 'true LOMG' and an LOMG/early-onset MG overlapping group of patients between 40 and 60.

Thymic function in juvenile idiopathic arthritis

OBJECTIVE

Thymic function declines exponentially with age. Impaired thymic function has been associated with autoimmune disease in adults but has never been formally assessed in childhood autoimmunity. Therefore, thymic function in children with the autoimmune disease juvenile idiopathic arthritis (JIA) was determined.

METHODS

Thymic function was measured in 70 children and young adults with JIA (age range 2.1-30.8 (median 10.4)) and 110 healthy age-matched controls using four independent assays. T cell receptor excision circles (WBLogTREC/ml) and the proportion of CD4(+) CD45RA(+)CD31(+) T cells (representing recent thymic emigrants; %RTEs) were quantified and intrathymic proliferation measured by calculating the alphaTREC/SigmabetaTREC ratio. Lastly, regulatory T cells (T(Reg)) of thymic origin (CD4(+)FOXP3(+)) were quantified in peripheral blood to assess the ability of the thymus in JIA to generate this T cell subset.

RESULTS

Thymic function was equivalent by all four parameters in JIA when compared with the control population. Furthermore, there was no consistent effect of JIA subtype on thymic function, although intrathymic proliferation was higher in the small rheumatoid factor (RF)(+) polyarticular group. There were no significant effects of disease-modifying antirheumatic drugs (DMARDs) or oral corticosteroids on thymic function, although those with the worst prognostic ILAR (International League of Associations for Rheumatology) subtypes were also those most likely to be on a DMARD.

CONCLUSIONS

It is demonstrated that children and young adults with JIA, unlike adults with autoimmune diseases, have thymic function that is comparable with that of healthy controls. The varied pathologies represented by the term "JIA" suggest this observation may not be disease specific and raises interesting questions about the aetiology of thymic impairment in adult autoimmunity.

Depletion of autoreactive immunologic memory followed by autologous hematopoietic stem cell transplantation in patients with refractory SLE induces long-term remission through de novo generation of a juvenile and tolerant immune system

Clinical trials have indicated that immunoablation followed by autologous hematopoietic stem cell transplantation (ASCT) has the potential to induce clinical remission in patients with refractory systemic lupus erythematosus (SLE), but the mechanisms have remained unclear. We now report the results of a single-center prospective study of long-term immune reconstitution after ASCT in 7 patients with SLE. The clinical remissions observed in these patients are accompanied by the depletion of autoreactive immunologic memory, reflected by the disappearance of pathogenic anti-double-stranded DNA (dsDNA) antibodies and protective antibodies in serum and a fundamental resetting of the adaptive immune system. The latter comprises recurrence of CD31(+)CD45RA(+)CD4(+) T cells (recent thymic emigrants) with a doubling in absolute numbers compared with age-matched healthy controls at the 3-year follow-up (P = .016), the regeneration of thymic-derived FoxP3(+) regulatory T cells, and normalization of peripheral T-cell receptor (TCR) repertoire usage. Likewise, responders exhibited normalization of the previously disturbed B-cell homeostasis with numeric recovery of the naive B-cell compartment within 1 year after ASCT. These data are the first to demonstrate that both depletion of the autoreactive immunologic memory and a profound resetting of the adaptive immune system are required to reestablish self-tolerance in SLE.

Influx of recent thymic emigrants into autoimmune thyroid disease glands in humans

Autoimmune thyroid diseases (AITD) are considered as prototypic organ-specific autoimmune diseases, yet their underlying aetiology remains poorly understood. Among the various pathophysiological mechanisms considered, a failure of central tolerance has received little attention. Here we present evidence in favour of dysregulated thymic function playing a role in AITD. Flow-cytometric analyses conducted in peripheral blood lymphocytes from 58 AITD patients and 48 age- and-sex-matched controls showed that AITD patients have significantly higher blood levels of CD4(+)CD45RA(+), CD4(+)CD31(+) and CD4/CD8 double-positive T lymphocytes, all markers of recent thymic emigrants (RTE). In addition, the alpha-signal joint T cell receptor excision circles (TRECs) content (a molecular marker of RTEs) was higher in the group of AITD patients older than 35 years than in age-matched controls. This was independent from peripheral T cell expansion as assessed by relative telomere length. Comparisons of TREC levels in peripheral blood lymphocytes and intrathyroidal lymphocytes in paired samples showed higher levels within the thyroid during the initial 30 months of the disease, indicating an influx of RTE into the thyroid during the initial stages of AITD. Additionally, a lack of correlation between TREC levels and forkhead box P3 expression suggests that the intrathyroidal RTE are not natural regulatory T cells. These results uncover a hitherto unknown correlation between altered thymic T cell export, the composition of intrathyroidal T cells and autoimmune pathology.

Decreased numbers of signal-joint T cell receptor excision circle-containing CD4+ and CD8+ cells in systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) patients have a decreased number of peripheral blood T cells containing signal-joint T cell receptor excision circles (Sj TRECs), which are considered an indicator of thymic output. The objective of this study was to investigate the mechanism of the decrease in such T cells. Peripheral blood T cells from SLE patients were classified into CD4+ and CD8+ cells. Sj TREC levels were measured by real-time PCR. Telomerase activity was determined by the telomeric repeat amplification protocol assay. The numbers of Sj TREC containing CD4+ and CD8+ cells were lower in the peripheral blood of SLE patients than in the controls. A correlation was found between the numbers of Sj TREC-positive CD4+ and CD8+ cells. The level of TRECs is influenced by an increase in cell division. To examine this increase, telomerase activity as an indicator of cell division was measured simultaneously; however, there was no correlation between the Sj TREC level and telomerase activity. These results suggest that decreased thymic output occurs in SLE patients.

Immune remodeling: lessons from repertoire alterations during chronological aging and in immune-mediated disease

Immunological studies of aging and of patients with chronic immune-mediated diseases document overlap of immune phenotypes. Here, the term "immune remodeling" refers to these phenotypes that are indicative of biological processes of deterioration and repair. This concept is explored through lessons from studies about the changes in the T-cell repertoire and the functional diversity of otherwise oligoclonal, senescent T cells. Immune remodeling suggests a gradual process that occurs throughout life. However, similar but more drastic remodeling occurs disproportionately among young patients with chronic disease. In this article, I propose that immune remodeling is a beneficial adaptation of aging to promote healthy survival beyond reproductive performance, but acute remodeling poses risk of premature exhaustion of the immune repertoire and, thus, is detrimental in young individuals.

Formation of non-random extrachromosomal elements during development, differentiation and oncogenesis

Extrachromosomal elements (EEs) were first discovered as minute chromatin bodies [Cox et al. Minute chromatin bodies in malignant tumors of childhood. Lancet 1965;62:55-8], and subsequently characterized as small circular DNA molecules physically separated from chromosomes. They include episomes, minichromosomes, small polydispersed DNAs or double minutes. This review focuses on eukaryotic EEs generated by genome rearrangements under physiological or pathological conditions. Some of those rearrangements occur randomly, but others are strictly non-random, highly regulated, and involve specific chromosomal locations (V(D)J-recombination, telomere maintenance mechanisms, c-myc deregulation). The multiple mechanisms of EEs formation are strongly interconnected and frequently linked to gene amplification. Identification of genes located on EEs will undoubtedly allow a better understanding of genome dynamics and oncogenic pathways.

Renewing the T cell repertoire to arrest autoimmune aggression

There is now evidence that high-dose immune ablation and autologous hematopoietic stem cell transplantation in humans triggers a reconstitution program that leads to the comprehensive renewal of the T cell repertoire. We argue here that several features of this program help to explain how autologous hematopoietic stem cell transplantation can induce long-term clinical remission from organ-specific-, as well as systemic, autoimmune diseases. We propose a model envisioning a coordinated sequence of events, rebuilding an immune system that is competent against infection but that is substantially reconfigured in a way that is less likely to redevelop autoimmunity.